Topic 4 · Density — the scripts
What you are deciding: go-ahead for video generation on this topic, card by card.
Out of scope: articles and PP100 items (not on this page).
Here: the intro video, 5 lesson videos (2 marked by the author as “could do without a video”) and the summary video, in teaching order. Each card: the script, the attached question, then the quiz the student meets after the video.
How: tap one button per card. Taps and notes save as you go and are sent; the Notes tab shows what has gone and re-sends.
Introduction: Density
Script
| Say | Screen |
|---|---|
| Here are two blocks, exactly the same size. | [two blocks side by side] |
| A student lifts them, and one is far harder to lift than the other. | [a hand lifts each; one barely moves] |
| She drops a steel bolt into water and it sinks; she drops a block of wood in and it floats. | [bucket of water; bolt sinks, wood floats] |
| She drops a small plastic bead into water and it floats, but in cooking oil the same bead sinks. | [two buckets; the bead floats in one, sinks in the other] |
| So why is one block so much harder to lift than the other, and what decides sink or float? | [the blocks and the buckets; question mark] |
| To find out, we will look at the mass and the volume of a thing, and what they decide about sinking and floating. | [a balance and a graduated cylinder beside the buckets] |
| Okay, so are you ready to find out what decides sink or float? | [the three replies appear] |
The ready line's poll — the attached item (no key; the intro teaches nothing)
Okay, so are you ready to find out what decides sink or float?
- A Yes, let's go! — Great. Here we go.
- B Not sure yet — That's fine. We take it one step at a time.
- C Let me watch that again — Good idea. Watch it again, then come back.
Answer
No key. A poll: every reply is accepted with its friendly line.
What to judge
Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?
8/10 on:
- Clear and concise language
- Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
- No "clangers" (content that causes a problematic misconception)
- Appropriate questions
- Initial testing
- Expansion into harder questions (no exam)
- The tasks should use similar language to that of the lesson
Gut check: better than the alternative? Would a student benefit? Full criteria
Find the volume of an odd-shaped solid
MAT-008 · Find the volume of an irregular solid by displacement — Calculate the volume of an irregular solid from the start and end readings of a graduated cylinder.
Script
| Say | Screen |
|---|---|
| A student wants the volume of a small stone. | [a lumpy stone; the student] |
| The stone is lumpy, so a ruler is no use. | [a ruler held against the stone; cross] |
| She has a graduated cylinder, a tall tube marked off in steps, holding forty milliliters of water. | [the cylinder; scale 0 to 100 mL; level at 40] |
| How can the water tell her the stone's volume? | [question mark] |
| The water will show the space the stone takes up. | [the water level highlighted] |
| She lowers the stone in, and the whole stone goes under. | [the stone sinks to the bottom] |
| The water level rises and settles at fifty-five milliliters. | [the level climbs from 40 to 55; label 55 mL] |
| The stone takes up space, so it pushes the water out of its way. | [zoom: the stone at the bottom; small arrows push water upward] |
| The level rose by exactly the stone's own volume. | [bracket from 40 to 55] |
| Pushing the water aside like this is called displacement. | [chip: DISPLACEMENT] |
| Fifty-five milliliters minus forty milliliters is fifteen milliliters: the stone displaced fifteen milliliters of water. | [55 mL − 40 mL = 15 mL] |
| One milliliter of water fills a cube one centimeter on each side, so one milliliter is one cubic centimeter. | [a 1 cm cube; 1 mL of water pours in and fills it; 1 mL = 1 cm³] |
| So the stone's volume is fifteen cubic centimeters. | [chip: 15 cm³] |
| Now consider a lump of clay. The level rises from forty milliliters to seventy milliliters, so the clay's volume is thirty cubic centimeters. | [clay lump; level 40 to 70; 30 cm³] |
| So, volume of the solid equals end reading minus start reading. | [the rule slide: the two cylinders at 40 mL and 55 mL with the bracket between; nothing else printed] |
| So for the stone, forty milliliters to fifty-five milliliters gives fifteen cubic centimeters. | [the stone's two cylinders; 15 cm³] |
| Okay, now your turn. | [the rule slide's images hold; closing screen: one line — “Volume of the solid equals end reading minus start reading.”] |
“Okay, now your turn.” — the attached question
A stone goes under the water in a graduated cylinder, and the level rises from 40 mL to 55 mL. What is the stone's volume?
- A 15 cm³
- B 40 cm³
- C 55 cm³
Answer
Key: A — 15 cm³
55 mL − 40 mL = 15 mL.
Each 1 mL displaced means 1 cm³ of solid, so the stone's volume is 15 cm³.
Feedback per option
- A 55 mL − 40 mL = 15 mL, and each 1 mL displaced means 1 cm³ of solid.
- B 40 mL is the start reading, the water alone.
- C 55 mL is the end reading, the water and the stone together.
Quiz after the video — the mastery check, 12 items
A student reads the scale on a graduated cylinder of juice. Which quantity has she measured?
- A the mass of the juice
- B the volume of the juice
- C the temperature of the juice
Answer
Key: B — the volume of the juice
You read the flat top of the liquid against the scale.
The reading is the liquid's volume, in milliliters.
Feedback per option
- A A balance measures mass.
- B A graduated cylinder measures volume, in milliliters.
- C A thermometer measures temperature.
A solid lowered under water pushes the water aside, so the water level rises. What is this pushing aside called?
Typed answer
Answer
Accepted: displacement
Pushing the water aside like this is called displacement.
A pebble is lowered into a graduated cylinder of water. What does displacement mean here?
- A The pebble pushes the water aside.
- B The pebble dissolves into the water.
- C The pebble soaks up some of the water.
Answer
Key: A — The pebble pushes the water aside.
The water that was in that space moves out of the way.
Pushing the water aside like this is called displacement.
Feedback per option
- A The pebble takes up space, so it pushes the water that was there out of its way.
- B A pebble does not dissolve. Displacement is the pebble pushing the water aside.
- C A pebble does not soak up water. Displacement is the pebble pushing the water aside.
The drawing shows the water before and after a steel nut goes under the water. What is the start reading, in mL?
Typed answer
Answer
Accepted: 60 mL · 60 · 60 ml · 60 milliliters
The flat top of the water sits exactly on the 60 mark.
So the start reading is 60 mL.
The drawing shows the water before and after a steel nut goes under the water. What is the end reading, in mL?
Typed answer
Answer
Accepted: 70 mL · 70 · 70 ml · 70 milliliters
The flat top of the water sits exactly on the 70 mark.
So the end reading is 70 mL.
The drawing shows the water before and after a steel nut goes under the water. What is the nut's volume, in cm³?
Typed answer
Answer
Accepted: 10 cm³ · 10 · 10 cm3 · 10 cubic centimeters
Volume of the solid equals end reading minus start reading: 70 mL − 60 mL = 10 mL.
Each 1 mL displaced means 1 cm³ of solid, so the nut's volume is 10 cm³.
A steel screw pushes aside 5 mL of water. What is the screw's volume, in cm³?
Typed answer
Answer
Accepted: 5 cm³ · 5 · 5 cm3 · 5 cubic centimeters
So each 1 mL displaced means 1 cm³ of solid.
The screw displaced 5 mL, so its volume is 5 cm³.
Water in a graduated cylinder reads 35 mL. A pebble goes under the water, and the level rises to 45 mL. What is the pebble's volume, in cm³?
Typed answer
Answer
Accepted: 10 cm³ · 10 · 10 cm3 · 10 cubic centimeters
45 mL − 35 mL = 10 mL.
Each 1 mL displaced means 1 cm³ of solid, so the pebble's volume is 10 cm³.
A toy car goes under the water in a graduated cylinder. The reading was 70 mL before and 90 mL after. What is the car's volume, in cm³?
Typed answer
Answer
Accepted: 20 cm³ · 20 · 20 cm3 · 20 cubic centimeters
90 mL − 70 mL = 20 mL.
Each 1 mL displaced means 1 cm³ of solid, so the car's volume is 20 cm³.
A lump of coal has a mass of 30 g. Water reads 50 mL before the coal goes under and 75 mL after. What is the coal's volume, in cm³?
Typed answer
Answer
Accepted: 25 cm³ · 25 · 25 cm3 · 25 cubic centimeters
Volume of the solid equals end reading minus start reading: 75 mL − 50 mL = 25 mL.
Each 1 mL displaced means 1 cm³ of solid, so the coal's volume is 25 cm³.
Hugo and Ines each measure the same pebble by displacement. Hugo starts with 30 mL of water and Ines with 60 mL. How do the two volumes they measure compare?
- A Hugo's is larger.
- B Ines's is larger.
- C The two volumes are the same.
Answer
Key: C — The two volumes are the same.
The start reading does not change the pebble.
Both students find the same rise, so both measure the same volume.
Feedback per option
- A The pebble pushes aside its own volume of water whatever the start reading.
- B More water at the start does not change how much the pebble pushes aside.
- C The pebble displaces its own volume of water in both cylinders.
Zara lowers a glass ornament into a graduated cylinder of water, and the level rises by 15 mL. Zara says: "So the ornament's mass is 15 g." Is Zara correct?
- A yes
- B no
Answer
Key: B — no
Each 1 mL displaced means 1 cm³ of solid, so its volume is 15 cm³.
Only a balance measures the mass, so Zara is not correct.
Feedback per option
- A A rise of 15 mL is a volume, not a mass. The ornament displaced 15 mL, so its volume is 15 cm³; only a balance gives its mass.
- B The rise in the water level is a volume. The ornament displaced 15 mL, so its volume is 15 cm³, and only a balance measures its mass.
What to judge
Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?
8/10 on:
- Clear and concise language
- Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
- No "clangers" (content that causes a problematic misconception)
- Appropriate questions
- Initial testing
- Expansion into harder questions (no exam)
- The tasks should use similar language to that of the lesson
Gut check: better than the alternative? Would a student benefit? Full criteria
Which is denser?
MAT-009 · What density is — Decide which of two objects is denser given their mass and volume, without calculating.
Script
| Say | Screen |
|---|---|
| Two blocks sit on a table, exactly the same size: one steel, one oak. | [two blocks side by side; labels STEEL, OAK] |
| A student lifts them, and the steel block is far harder to lift. | [a hand lifts each; the steel one barely moves] |
| On a balance, the steel reads four hundred grams and the oak thirty-five grams. | [two balances: 400 g, 35 g] |
| They are the same size but not the same mass, so what is different about the steel? | [question mark] |
| It packs more mass into the same space. | [the steel block highlighted] |
| Each block has a volume of fifty cubic centimeters. | [labels: 50 cm³ under each block] |
| The steel packs four hundred grams into that space; the oak packs only thirty-five grams. | [chips: 400 g IN 50 cm³; 35 g IN 50 cm³] |
| So the steel packs far more mass into each cubic centimeter. | [zoom on one 1 cm cube of each block] |
| How much mass a material packs into each cubic centimeter is called its density. | [chip: DENSITY] |
| Same volume and more mass means denser: steel is denser than oak. | [verdict: STEEL IS DENSER] |
| Now consider a steel ball and a glass ball that both read forty grams. | [two balances, both 40 g; small dark ball, bigger clear ball] |
| The steel ball is five cubic centimeters; the glass ball is sixteen cubic centimeters. | [labels: 5 cm³, 16 cm³] |
| The steel packs the same mass into less space, so the steel ball is denser. | [verdict: STEEL IS DENSER] |
| So, here's what we've seen. Same volume and more mass means denser. | [the rule slide: the table of the two pairs; the blocks row highlighted; nothing else printed] |
| Same mass and less volume means denser. | [the balls row highlighted] |
| Okay, now your turn. | [the rule slide's images hold; closing screen: bullets — • Same volume and more mass means denser. • Same mass and less volume means denser.] |
“Okay, now your turn.” — the attached question
A steel block and an oak block are the same size. The steel reads 400 g and the oak 35 g. Which is denser?
- A The oak block is denser.
- B The two blocks have the same density.
- C The steel block is denser.
Answer
Key: C — The steel block is denser.
The steel block has far more mass: 400 g against 35 g.
Same volume and more mass means denser, so the steel block is denser.
Feedback per option
- A The oak has far less mass in the same volume.
- B The volumes match, but the masses differ.
- C Same volume, and the steel has far more mass.
Quiz after the video — the mastery check, 13 items
A balance reads 3 kg for a watermelon. What does the reading tell you?
- A how much space the watermelon takes up
- B how much material is in the watermelon
Answer
Key: B — how much material is in the watermelon
Mass is the amount of material in something.
So 3 kg is the amount of material in the watermelon.
Feedback per option
- A A balance does not measure space. The amount of space something takes up is its volume.
- B A balance measures mass: the amount of material in the thing on it.
What is the volume of a shoe box?
- A the amount of material in the box
- B the amount of space the box takes up
- C how long the box is
Answer
Key: B — the amount of space the box takes up
So the box's volume is the amount of space the box takes up.
Feedback per option
- A The amount of material in something is its mass.
- B Volume is the amount of space something takes up.
- C Length is one distance. Volume is the amount of space something takes up.
How much mass a material packs into each cubic centimeter is called its…
Typed answer
Answer
Accepted: density
What is density?
- A the amount of space an object takes up
- B the amount of material in an object
- C the mass packed into each cubic centimeter
Answer
Key: C — the mass packed into each cubic centimeter
Feedback per option
- A The amount of space something takes up is its volume.
- B The amount of material in something is its mass.
- C Density is how much mass a material packs into each cubic centimeter.
Which is denser?
- A The brass block is denser.
- B The pine block is denser.
- C The two blocks have the same density.
Answer
Key: A — The brass block is denser.
The brass block has more mass: 170 g against 10 g.
Same volume and more mass means denser, so the brass block is denser.
Feedback per option
- A Same volume, and the brass has more mass.
- B The pine has less mass in the same volume.
- C The volumes match, but the masses differ.
Which is denser?
- A The candle stub is denser.
- B The lead sinker is denser.
- C The candle stub and the sinker have the same density.
Answer
Key: B — The lead sinker is denser.
The lead sinker has more mass: 113 g against 9 g.
Same volume and more mass means denser, so the lead sinker is denser.
Feedback per option
- A The candle stub has less mass in the same volume.
- B Same volume, and the lead sinker has more mass.
- C The volumes match, but the masses differ.
Which is denser?
- A The steel hinge is denser.
- B The maple ruler is denser.
- C The hinge and the ruler have the same density.
Answer
Key: A — The steel hinge is denser.
The steel hinge has less volume: 7 cm³ against 80 cm³.
Same mass and less volume means denser, so the steel hinge is denser.
Feedback per option
- A Same mass, and the hinge packs it into less volume.
- B The ruler spreads the same mass over more volume.
- C The masses match, but the volumes differ.
Which is denser?
- A The bar of soap is denser.
- B The glass pebble is denser.
- C The soap and the pebble have the same density.
Answer
Key: B — The glass pebble is denser.
The glass pebble has less volume: 10 cm³ against 25 cm³.
Same mass and less volume means denser, so the glass pebble is denser.
Feedback per option
- A The soap spreads the same mass over more volume.
- B Same mass, and the pebble packs it into less volume.
- C The masses match, but the volumes differ.
Which is denser?
- A The piece of brick is denser.
- B The copper fitting is denser.
- C The brick and the fitting have the same density.
Answer
Key: B — The copper fitting is denser.
The copper fitting has more mass: 445 g against 95 g.
Same volume and more mass means denser, so the copper fitting is denser.
Feedback per option
- A The brick has less mass in the same volume.
- B Same volume, and the copper has more mass.
- C The volumes match, but the masses differ.
Which is denser?
- A The ice cube is denser.
- B The cork stopper is denser.
- C The ice cube and the cork have the same density.
Answer
Key: A — The ice cube is denser.
The ice cube has more mass: 27 g against 6 g.
Same volume and more mass means denser, so the ice cube is denser.
Feedback per option
- A Same volume, and the ice has more mass.
- B The cork has less mass in the same volume.
- C The volumes match, but the masses differ.
Which is denser?
- A The maple spoon is denser.
- B The beech spoon is denser.
- C The two spoons have the same density.
Answer
Key: C — The two spoons have the same density.
Both spoons have a volume of 50 cm³.
Same mass packed into the same volume means the same density.
Feedback per option
- A Maple may seem the denser wood, but both spoons have 35 g in 50 cm³. Same mass in the same volume means the same density.
- B Beech may seem the denser wood, but both spoons have 35 g in 50 cm³. Same mass in the same volume means the same density.
- C Same mass in the same volume means the same density.
Malik reads the table. He says: "The ring and the coaster have the same mass, so they have the same density." Is Malik correct?
- A yes
- B no
Answer
Key: B — no
The silver ring has far less volume: 2 cm³ against 105 cm³.
Same mass and less volume means denser, so the ring is denser and Malik is not correct.
Feedback per option
- A Same mass does not mean same density. The ring packs its 21 g into 2 cm³; the coaster spreads its 21 g over 105 cm³.
- B The masses match, but the ring packs its 21 g into 2 cm³ and the coaster spreads its 21 g over 105 cm³, so the ring is denser.
Elena reads the table. She says: "The bag of feathers has more mass, so the feathers are denser." Is Elena correct?
- A yes
- B no
Answer
Key: B — no
The bag spreads its 300 g over 30,000 cm³.
The pebble packs its 135 g into 50 cm³, far more mass in each cubic centimeter.
So the pebble is denser, and Elena is not correct.
Feedback per option
- A More mass means denser only when the volumes match. The bag spreads 300 g over 30,000 cm³; the pebble packs 135 g into 50 cm³.
- B The pebble packs 135 g into 50 cm³, while the bag spreads 300 g over 30,000 cm³, so the pebble is denser.
What to judge
Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?
8/10 on:
- Clear and concise language
- Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
- No "clangers" (content that causes a problematic misconception)
- Appropriate questions
- Initial testing
- Expansion into harder questions (no exam)
- The tasks should use similar language to that of the lesson
Gut check: better than the alternative? Would a student benefit? Full criteria
Calculate density
MAT-010 · Calculate density — Calculate the density of a substance from its mass and volume, with correct units.
Script
| Say | Screen |
|---|---|
| A steel cube has a mass of forty-eight grams and a volume of six cubic centimeters. | [steel cube; chips: 48 g, 6 cm³] |
| An oak block has a mass of fifty-six grams and a volume of eighty cubic centimeters. | [oak block; chips: 56 g, 80 cm³] |
| Neither the masses nor the volumes match, so comparing cannot decide. | [the two pairs of chips; cross over the comparison] |
| How dense is each one, as a number? | [question mark] |
| The steel packs forty-eight grams into six cubic centimeters. | [the cube split into six 1 cm cubes] |
| If we share the forty-eight grams equally between the six cubic centimeters, each one gets eight grams. | [8 g lands on each small cube] |
| So the steel's density is eight grams per cubic centimeter. | [chip: 8 g/cm³; the unit spelled out beneath] |
| To find a density, divide the mass by the volume: density equals mass divided by volume. | [equation: density = mass ÷ volume, terms labelled] |
| Now for the oak, fifty-six grams divided by eighty cubic centimeters gives zero point seven grams per cubic centimeter. | [worked form for the oak fills line by line] |
| Now consider an aluminum bar: eighty-one grams divided by thirty cubic centimeters gives two point seven grams per cubic centimeter. | [aluminum bar; worked form; 2.7 g/cm³] |
| Every time, write the values, the equation, the substitution, the calculation, and the answer with its unit. | [the five line labels appear in turn] |
| So, density equals mass divided by volume, in grams per cubic centimeter. | [the rule slide: the equation card density = mass ÷ volume with its key; nothing else printed] |
| So the steel at eight grams per cubic centimeter is denser than the oak at zero point seven grams per cubic centimeter. | [table: steel 8 g/cm³, oak 0.7 g/cm³] |
| Okay, now your turn. | [the rule slide's images hold; closing screen: one line — “Density equals mass divided by volume, in grams per cubic centimeter.”] |
“Okay, now your turn.” — the attached question
A steel cube packs 48 g into 6 cm³. What is the steel's density?
- A 8 g/cm³
- B 42 g/cm³
- C 288 g/cm³
Answer
Key: A — 8 g/cm³
48 g ÷ 6 cm³ = 8 g/cm³.
Feedback per option
- A 48 g ÷ 6 cm³ = 8 g/cm³.
- B 48 − 6 = 42, but density is mass divided by volume, not mass minus volume.
- C 48 × 6 = 288, but density is mass divided by volume, not mass times volume.
Quiz after the video — the mastery check, 12 items
Two objects have the same volume. Which one is denser?
- A the one with more mass
- B the one with less mass
Answer
Key: A — the one with more mass
Same volume and more mass means denser.
Feedback per option
- A Same volume and more mass means denser.
- B Less mass in the same volume means less dense.
A pebble displaces 12 mL of water. What is the pebble's volume, in cm³?
Typed answer
Answer
Accepted: 12 cm³ · 12 · 12 cm3 · 12 cubic centimeters
The pebble displaced 12 mL, so its volume is 12 cm³.
Which unit is a density written in?
- A g
- B cm³
- C g/cm³
Answer
Key: C — g/cm³
The mass is in g and the volume is in cm³, so the density is in g/cm³.
Feedback per option
- A Grams are the unit of mass.
- B Cubic centimeters are the unit of volume.
- C Grams per cubic centimeter: the mass in each cubic centimeter.
A material has a density of 2.5 g/cm³. What does that mean?
- A The whole piece has a mass of 2.5 g.
- B The whole piece has a volume of 2.5 cm³.
- C Each cubic centimeter has a mass of 2.5 g.
Answer
Key: C — Each cubic centimeter has a mass of 2.5 g.
2.5 g/cm³ means each cubic centimeter has a mass of 2.5 g.
Feedback per option
- A A density is not the mass of the whole piece. It is the mass in each cubic centimeter.
- B A density is not a volume. It is the mass in each cubic centimeter.
- C Grams per cubic centimeter: each cubic centimeter of the material has a mass of 2.5 g.
A glass block has a mass of 50 g and a volume of 20 cm³. Which equation gives its density?
- A density = mass ÷ volume
- B density = volume ÷ mass
- C density = mass × volume
Answer
Key: A — density = mass ÷ volume
To share the mass out over the volume, divide the mass by the volume.
So density = mass ÷ volume.
Feedback per option
- A Density is the mass shared out over the volume, so divide the mass by the volume.
- B Dividing the volume by the mass gives the space for each gram, not the mass in each cubic centimeter.
- C Multiplying does not share the mass out over the volume.
A glass block has a mass of 50 g and a volume of 20 cm³. Which line substitutes the values correctly?
- A density = 20 cm³ ÷ 50 g
- B density = 50 g ÷ 20 cm³
- C density = 50 g × 20 cm³
Answer
Key: B — density = 50 g ÷ 20 cm³
Put the mass, 50 g, in place of mass and the volume, 20 cm³, in place of volume.
So density = 50 g ÷ 20 cm³.
Feedback per option
- A The mass goes first: mass ÷ volume.
- B Mass ÷ volume: 50 g ÷ 20 cm³.
- C The equation divides; it does not multiply.
A glass block has a mass of 50 g and a volume of 20 cm³. Calculate its density, in g/cm³.
Typed answer
Answer
Accepted: 2.5 g/cm³ · 2.5 · 2.5 g/cm3 · 2.5 grams per cubic centimeter
Equation: density = mass ÷ volume.
Substitute: density = 50 g ÷ 20 cm³.
Calculate: 50 ÷ 20 = 2.5.
Answer: density = 2.5 g/cm³.
A glass block's density comes out as 2.5. Which is the answer written with its unit?
- A 2.5 g
- B 2.5 cm³
- C 2.5 g/cm³
Answer
Key: C — 2.5 g/cm³
Dividing g by cm³ gives g/cm³.
So the answer is 2.5 g/cm³.
Feedback per option
- A Grams alone is a mass.
- B Cubic centimeters alone is a volume.
- C Mass in grams divided by volume in cubic centimeters gives grams per cubic centimeter.
A copper pipe has a mass of 178 g and a volume of 20 cm³. What is the density of copper, in g/cm³?
Typed answer
Answer
Accepted: 8.9 g/cm³ · 8.9 · 8.9 g/cm3 · 8.9 grams per cubic centimeter
Equation: density = mass ÷ volume.
Substitute: density = 178 g ÷ 20 cm³.
Calculate: 178 ÷ 20 = 8.9.
Answer: density = 8.9 g/cm³.
A pine board has a mass of 25 g and a volume of 50 cm³. What is the density of pine, in g/cm³?
Typed answer
Answer
Accepted: 0.5 g/cm³ · 0.5 · .5 · 0.5 g/cm3 · 0.5 grams per cubic centimeter
Equation: density = mass ÷ volume.
Substitute: density = 25 g ÷ 50 cm³.
Calculate: 25 ÷ 50 = 0.5.
Answer: density = 0.5 g/cm³.
A granite pebble has a mass of 54 g. Water in a graduated cylinder reads 40 mL before the pebble goes under and 60 mL after. What is the density of granite, in g/cm³?
Typed answer
Answer
Accepted: 2.7 g/cm³ · 2.7 · 2.7 g/cm3 · 2.7 grams per cubic centimeter
Values: mass = 54 g, volume = 20 cm³.
Equation: density = mass ÷ volume.
Substitute: density = 54 g ÷ 20 cm³.
Calculate: 54 ÷ 20 = 2.7.
Answer: density = 2.7 g/cm³.
A brick has a mass of 190 g and a volume of 100 cm³. Layla says: "Density is volume divided by mass, so I work out 100 ÷ 190." Is Layla correct?
- A yes
- B no
Answer
Key: B — no
So the mass is divided by the volume, not the other way round.
190 g ÷ 100 cm³ = 1.9 g/cm³, and Layla is not correct.
Feedback per option
- A Volume divided by mass is the wrong way round. Density is mass divided by volume: 190 g ÷ 100 cm³ = 1.9 g/cm³.
- B Density is mass divided by volume: 190 g ÷ 100 cm³ = 1.9 g/cm³.
What to judge
Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?
8/10 on:
- Clear and concise language
- Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
- No "clangers" (content that causes a problematic misconception)
- Appropriate questions
- Initial testing
- Expansion into harder questions (no exam)
- The tasks should use similar language to that of the lesson
Gut check: better than the alternative? Would a student benefit? Full criteria
Will it sink or float?
MAT-011 · Relative density predicts sinking and floating — Predict whether an object will sink or float in a given liquid by comparing their densities.
Script
| Say | Screen |
|---|---|
| A student drops a steel bolt into water, and it sinks. | [bucket of water; bolt drops to the bottom] |
| She drops a block of wood in, and it floats. | [wood block bobs at the surface] |
| Then she drops a small plastic bead in, and it floats. | [bead floats; chip: FLOATS] |
| The same bead in a bucket of cooking oil sinks. | [second bucket, OIL; the bead drops to the bottom; chip: SINKS] |
| The same bead in two liquids gives two outcomes, so what decides? | [question mark between the buckets] |
| Density decides. | [chip: DENSITY DECIDES] |
| Density is mass divided by volume, in grams per cubic centimeter. | [chip: DENSITY = MASS ÷ VOLUME] |
| Water is one point zero grams per cubic centimeter. | [label on the water: 1.0 g/cm³] |
| Steel is eight grams per cubic centimeter, denser than water, so the bolt sinks. | [label: bolt 8 g/cm³; arrow down] |
| Wood is zero point seven grams per cubic centimeter, less dense than water, so the wood floats. | [label: wood 0.7 g/cm³; arrow up] |
| The bead is zero point nine five grams per cubic centimeter, less dense than water, so it floats. | [label: bead 0.95 g/cm³; floats] |
| Cooking oil is zero point nine two grams per cubic centimeter, so in oil the bead is denser, and it sinks. | [label on the oil: 0.92 g/cm³; bead sinks] |
| A huge oak log floats and a tiny steel nut sinks: density decides, not mass. | [log floating; nut on the bottom; chip: DENSITY DECIDES] |
| So, an object denser than the liquid sinks. An object less dense than the liquid floats. | [the rule slide: the two buckets with the bead; nothing else printed] |
| So the bead is less dense than the water and denser than the oil. | [the bead in both buckets with all three densities] |
| Okay, now your turn. | [the rule slide's images hold; closing screen: bullets — • An object denser than the liquid sinks. • An object less dense than the liquid floats.] |
“Okay, now your turn.” — the attached question
A plastic bead floats in water and sinks in cooking oil. Which liquid is denser than the bead?
- A the cooking oil
- B the water
Answer
Key: B — the water
The bead floats in the water, so the water is denser than the bead.
The bead sinks in the oil, so the oil is less dense than the bead.
Feedback per option
- A The bead sinks in the oil, so the oil is less dense than the bead.
- B The bead floats in water, so the water is denser than the bead.
Quiz after the video — the mastery check, 12 items
A metal has a density of 7.9 g/cm³. What does that number tell you?
- A Each cubic centimeter of the metal has a mass of 7.9 g.
- B The piece of metal has a mass of 7.9 g.
- C The piece of metal has a volume of 7.9 cm³.
Answer
Key: A — Each cubic centimeter of the metal has a mass of 7.9 g.
7.9 g/cm³ means each cubic centimeter of the metal has a mass of 7.9 g.
Feedback per option
- A Density is the mass packed into each cubic centimeter.
- B A density is not the mass of the whole piece.
- C A density is not a volume.
A steel spoon is dropped into a bowl full of water. What happens to the spoon?
- A The spoon sinks.
- B The spoon floats.
Answer
Key: A — The spoon sinks.
So the spoon drops to the bottom of the bowl.
Feedback per option
- A Steel sinks in water.
- B A steel spoon drops to the bottom of the bowl.
Sink or float?
- A sinks
- B floats
Answer
Key: B — floats
The oak block at 0.7 g/cm³ is less dense than water at 1.0 g/cm³.
An object less dense than the liquid floats.
Feedback per option
- A The oak at 0.7 g/cm³ is less dense than the water at 1.0 g/cm³.
- B The oak at 0.7 g/cm³ is less dense than the water at 1.0 g/cm³, so it floats.
Sink or float?
- A sinks
- B floats
Answer
Key: A — sinks
The glass marble at 2.5 g/cm³ is denser than water at 1.0 g/cm³.
An object denser than the liquid sinks.
Feedback per option
- A The marble at 2.5 g/cm³ is denser than the water at 1.0 g/cm³, so it sinks.
- B The marble at 2.5 g/cm³ is denser than the water at 1.0 g/cm³.
Sink or float?
- A sinks
- B floats
Answer
Key: A — sinks
The ebony block at 1.2 g/cm³ is denser than water at 1.0 g/cm³.
An object denser than the liquid sinks, even a wooden one.
Feedback per option
- A The ebony at 1.2 g/cm³ is denser than the water at 1.0 g/cm³, so it sinks.
- B Ebony is a wood, but at 1.2 g/cm³ it is denser than water at 1.0 g/cm³.
Sink or float?
- A sinks
- B floats
Answer
Key: A — sinks
The grape at 1.1 g/cm³ is denser than water at 1.0 g/cm³.
An object denser than the liquid sinks.
Feedback per option
- A The grape at 1.1 g/cm³ is denser than the water at 1.0 g/cm³, so it sinks.
- B The grape at 1.1 g/cm³ is denser than the water at 1.0 g/cm³.
Sink or float?
- A sinks
- B floats
Answer
Key: B — floats
The grape at 1.1 g/cm³ is less dense than salt water at 1.2 g/cm³.
An object less dense than the liquid floats.
Feedback per option
- A The grape at 1.1 g/cm³ is less dense than the salt water at 1.2 g/cm³.
- B The grape at 1.1 g/cm³ is less dense than the salt water at 1.2 g/cm³, so it floats.
Sink or float?
- A sinks
- B floats
Answer
Key: B — floats
The candle at 0.9 g/cm³ is less dense than honey at 1.4 g/cm³.
An object less dense than the liquid floats.
Feedback per option
- A The candle at 0.9 g/cm³ is less dense than the honey at 1.4 g/cm³.
- B The candle at 0.9 g/cm³ is less dense than the honey at 1.4 g/cm³, so it floats.
Sink or float?
- A sinks
- B floats
Answer
Key: A — sinks
The eraser at 1.2 g/cm³ is denser than water at 1.0 g/cm³.
An object denser than the liquid sinks.
Feedback per option
- A The eraser at 1.2 g/cm³ is denser than the water at 1.0 g/cm³, so it sinks.
- B The eraser at 1.2 g/cm³ is denser than the water at 1.0 g/cm³.
Sink or float?
- A sinks
- B floats
Answer
Key: B — floats
The pumice stone at 0.6 g/cm³ is less dense than water at 1.0 g/cm³.
An object less dense than the liquid floats, even a stone.
Feedback per option
- A The pumice at 0.6 g/cm³ is less dense than the water at 1.0 g/cm³.
- B Pumice is a stone, but at 0.6 g/cm³ it is less dense than water at 1.0 g/cm³, so it floats.
Water has a density of 1.0 g/cm³. Isla reads the table. She says: "The log has far more mass than the pebble, so in water the log will sink and the pebble will float." Is Isla correct?
- A yes
- B no
Answer
Key: B — no
The oak log at 0.7 g/cm³ is less dense than water at 1.0 g/cm³, so the log floats.
The granite pebble at 2.7 g/cm³ is denser than water, so the pebble sinks.
So Isla is not correct.
Feedback per option
- A Mass does not decide sinking; density does. The log at 0.7 g/cm³ is less dense than water and floats; the pebble at 2.7 g/cm³ sinks.
- B Density decides. The log at 0.7 g/cm³ is less dense than water and floats; the pebble at 2.7 g/cm³ sinks.
A plastic button sinks in water. The button is dropped into honey instead. Sink or float?
- A sinks
- B floats
Answer
Key: B — floats
The button at 1.2 g/cm³ is less dense than honey at 1.4 g/cm³.
An object less dense than the liquid floats, so in honey the button floats.
Feedback per option
- A The button at 1.2 g/cm³ sank in water, but honey at 1.4 g/cm³ is denser than the button.
- B The button at 1.2 g/cm³ is less dense than honey at 1.4 g/cm³, so in honey it floats.
What to judge
Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?
8/10 on:
- Clear and concise language
- Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
- No "clangers" (content that causes a problematic misconception)
- Appropriate questions
- Initial testing
- Expansion into harder questions (no exam)
- The tasks should use similar language to that of the lesson
Gut check: better than the alternative? Would a student benefit? Full criteria
Density does not depend on how much you have
MAT-015 · Characteristic properties do not depend on the amount of a substance — Explain why the density of a small sample and a large sample of the same substance are identical.
Script
| Say | Screen |
|---|---|
| A steel cube, forty-eight grams and six cubic centimeters, has a density of eight grams per cubic centimeter. | [the cube; chips: 48 g, 6 cm³, 8 g/cm³] |
| A student saws the cube in half. | [saw cuts the cube; two halves] |
| Each half is twenty-four grams and three cubic centimeters. | [labels under each half: 24 g, 3 cm³] |
| Is each half less dense than the whole cube? | [question mark] |
| No, it is not. | [cross on the question mark] |
| Density equals mass divided by volume: twenty-four grams divided by three cubic centimeters is eight grams per cubic centimeter. | [worked form: 24 g ÷ 3 cm³ = 8 g/cm³] |
| Each half has the same density as the whole cube. | [table: whole 8 g/cm³, half 8 g/cm³] |
| Cutting the cube in half halved the mass and halved the volume. | [48 g → 24 g; 6 cm³ → 3 cm³] |
| Half the mass shared over half the volume still gives eight grams in each cubic centimeter. | [one small 1 cm cube: 8 g] |
| So density belongs to the material, not to the size of the piece. | [chip: DENSITY BELONGS TO THE MATERIAL] |
| Now consider a gold ring of one cubic centimeter and nineteen point three grams, and a gold bar a hundred times bigger. | [ring: 19.3 g, 1 cm³; bar: 1930 g, 100 cm³] |
| The bar has a hundred times the mass and a hundred times the volume, so both are nineteen point three grams per cubic centimeter. | [19.3 ÷ 1 = 19.3; 1930 ÷ 100 = 19.3; ×100 on both rows] |
| A steel filing and a steel girder are both eight grams per cubic centimeter. | [filing and girder: 8 g/cm³] |
| Here's the pattern. A small sample and a large sample of the same material have the same density. | [the rule slide: the cube and its halves, each at 8 g/cm³; nothing else printed] |
| Okay, now your turn. | [the rule slide's images hold; closing screen: one line — “A small sample and a large sample of the same material have the same density.”] |
“Okay, now your turn.” — the attached question
A steel cube is sawn in half. Each half is 24 g and 3 cm³. What is the density of each half?
- A 4 g/cm³
- B 8 g/cm³
- C 16 g/cm³
Answer
Key: B — 8 g/cm³
24 g ÷ 3 cm³ = 8 g/cm³.
Each half has the same density as the whole cube.
Feedback per option
- A Halving the cube does not halve the density: 24 g ÷ 3 cm³ = 8 g/cm³.
- B 24 g ÷ 3 cm³ = 8 g/cm³, the same as the whole cube.
- C Halving the cube does not double the density: 24 g ÷ 3 cm³ = 8 g/cm³.
Quiz after the video — the mastery check, 10 items
A piece of steel has a mass of 40 g and a volume of 5 cm³. What is its density, in g/cm³?
Typed answer
Answer
Accepted: 8 g/cm³ · 8 · 8 g/cm3 · 8 grams per cubic centimeter
Equation: density = mass ÷ volume.
Substitute: density = 40 g ÷ 5 cm³.
Calculate: 40 ÷ 5 = 8.
Answer: density = 8 g/cm³.
A whole ceramic tile sinks in water. A small chip breaks off the same tile. Does the chip sink too?
- A yes
- B no
Answer
Key: A — yes
The same material behaves the same way in water.
So the chip sinks too.
Feedback per option
- A The chip is the same material as the tile, so it behaves the same way in water.
- B The chip is the same material as the tile, so it sinks just like the tile.
The coin and the tray are both silver. Which is denser?
- A The coin is denser.
- B The tray is denser.
- C The coin and the tray have the same density.
Answer
Key: C — The coin and the tray have the same density.
For the tray: 2100 g ÷ 200 cm³ = 10.5 g/cm³.
Density belongs to the material, so the coin and the tray have the same density.
Feedback per option
- A The coin has less mass and less volume, in the same ratio.
- B The tray has more mass and more volume, in the same ratio.
- C Both silver: 21 g ÷ 2 cm³ and 2100 g ÷ 200 cm³ both equal 10.5 g/cm³.
A copper pipe has a mass of 445 g and a volume of 50 cm³. A plumber cuts off a short piece of 89 g and 10 cm³. Explain why the short piece has the same density as the pipe.
Starter: The short piece has the same density because…
Answer
Model answer · ["the whole pipe's density: 445 g ÷ 50 cm³ = 8.9 g/cm³", 'the piece has less mass and less volume in the same ratio (20% of each)', "the piece's density: 89 g ÷ 10 cm³ = 8.9 g/cm³, so each cubic centimeter of copper has the same mass whatever the size"] points
The whole pipe has a density of 445 g ÷ 50 cm³, which equals 8.9 g/cm³.
Cutting off the piece took 20% of the mass (89 g of 445 g) and 20% of the volume (10 cm³ of 50 cm³).
The short piece has a density of 89 g ÷ 10 cm³, which also equals 8.9 g/cm³.
Each cubic centimeter of copper has a mass of 8.9 g, whatever the size of the piece.
A silver coin and a silver tray are both pure silver. Felix says: "The tray is denser than the coin, because the tray has far more mass." Is Felix correct?
- A yes
- B no
Answer
Key: B — no
The tray also has more volume, in the same ratio.
So each cubic centimeter of silver has the same mass in both.
Density belongs to the material, so Felix is not correct.
Feedback per option
- A More mass does not make silver denser. The tray has more mass and more volume in the same ratio, so each cubic centimeter has the same mass.
- B The tray has more mass and more volume in the same ratio, so each cubic centimeter of silver has the same mass.
A full glass of water has a density of 1.0 g/cm³. Half the water is poured away. What is the density of the water left, in g/cm³?
Typed answer
Answer
Accepted: 1.0 g/cm³ · 1.0 · 1 · 1 g/cm³ · 1.0 g/cm3 · 1 g/cm3
Half the mass shared over half the volume gives the same mass in each cubic centimeter.
Density belongs to the material, so the water left is still 1.0 g/cm³.
A drop of honey and a full jar of honey come from the same bottle. Which is denser?
- A The drop is denser.
- B The jar of honey is denser.
- C The drop and the jar of honey have the same density.
Answer
Key: C — The drop and the jar of honey have the same density.
Density belongs to the material, not to the size of the sample.
So the drop and the jar of honey have the same density.
Feedback per option
- A The drop has less mass and less volume in the same ratio.
- B The jar has more mass and more volume in the same ratio.
- C Same honey, same density, whatever the amount.
A large iron anchor has a density of 7.9 g/cm³. What is the density of a small iron nail, in g/cm³?
Typed answer
Answer
Accepted: 7.9 g/cm³ · 7.9 · 7.9 g/cm3 · 7.9 grams per cubic centimeter
Density belongs to the material, not to the size of the piece.
So the nail's density is also 7.9 g/cm³.
An aluminum spoon has a mass of 27 g and a density of 2.7 g/cm³. An aluminum pan has a mass of 270 g. What is the pan's density, in g/cm³?
Typed answer
Answer
Accepted: 2.7 g/cm³ · 2.7 · 2.7 g/cm3 · 2.7 grams per cubic centimeter
Each cubic centimeter of aluminum still has a mass of 2.7 g.
So the pan's density is 2.7 g/cm³.
A stick of chalk has a density of 2.5 g/cm³. Grace snaps it in half. She says: "Each half still has a density of 2.5 g/cm³." Is Grace correct?
- A yes
- B no
Answer
Key: A — yes
Snapping the chalk in half also halves the volume.
Half the mass over half the volume gives the same mass in each cubic centimeter.
So each half is still 2.5 g/cm³, and Grace is correct.
Feedback per option
- A Snapping the chalk halves the mass and the volume together, so each cubic centimeter still has a mass of 2.5 g.
- B Snapping does not change what the chalk is made of. Half the mass over half the volume is still 2.5 g in each cubic centimeter.
What to judge
Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?
8/10 on:
- Clear and concise language
- Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
- No "clangers" (content that causes a problematic misconception)
- Appropriate questions
- Initial testing
- Expansion into harder questions (no exam)
- The tasks should use similar language to that of the lesson
Gut check: better than the alternative? Would a student benefit? Full criteria
Summary: Density
Script, part 1 (122 words)
| Say | Screen |
|---|---|
| Here is everything we found out about density. | [a still: the cylinder with the stone, the two blocks, the two buckets] |
| To find the volume of an odd-shaped solid, read the water level before and after the whole solid goes under. | [the cylinder; two levels marked] |
| The solid pushes aside exactly its own volume of water: that is displacement. | [chip: DISPLACEMENT] |
| Volume of the solid equals end reading minus start reading. | [chip: VOLUME = END READING − START READING] |
| Each one milliliter of water displaced means one cubic centimeter of solid. | [the 1 cm cube; 1 mL = 1 cm³] |
| Density is how much mass a material packs into each cubic centimeter. | [chip: DENSITY] |
| Same volume and more mass means denser. Same mass and less volume means denser. | [the table of the two pairs] |
| Density equals mass divided by volume, in grams per cubic centimeter. | [the equation card with its key] |
| To calculate it, write the values, the equation, the substitution, the calculation, and the answer with its unit. | [the five line labels] |
| Okay, now your turn. | [the equation card holds] |
“Okay, now your turn.” — the check question between the parts
Two blocks have the same volume. The steel block has more mass than the oak block. Which is denser?
- A the steel block
- B the oak block
- C They have the same density.
Answer
Key: A — the steel block
So the steel block is denser.
Feedback per option
- A Same volume and more mass means denser.
- B The oak block has less mass in the same volume, so it is less dense.
- C The volumes match, but the masses differ, so the densities differ.
Script, part 2 (90 words)
| Say | Screen |
|---|---|
| Here is everything we found out about sinking, floating and the size of the piece. | [a still: the two buckets and the cube with its halves] |
| To predict sinking or floating, compare the object's density with the liquid's density. | [the two buckets] |
| An object denser than the liquid sinks. An object less dense than the liquid floats. | [chips: DENSER SINKS; LESS DENSE FLOATS] |
| Density decides, not mass: a huge oak log floats and a tiny steel nut sinks. | [log floating; nut on the bottom; chip: DENSITY DECIDES] |
| Density belongs to the material, not to the size of the piece. | [chip: DENSITY BELONGS TO THE MATERIAL] |
| So a small sample and a large sample of the same material have the same density. | [the cube and its halves, each at 8 g/cm³] |
| Okay, now your turn. | [the cube and its halves hold] |
“Okay, now your turn.” — the two questions after part 2
A steel filing and a steel girder are both made of steel. Which is denser?
- A The filing is denser.
- B The girder is denser.
- C Neither: both are 8 g/cm³.
Answer
Key: C — Neither: both are 8 g/cm³.
Density belongs to the material, not to the size of the piece.
So both have a density of 8 g/cm³.
Feedback per option
- A The filing is steel, so each cubic centimeter of it has a mass of 8 g, just like the girder.
- B The girder has more mass and more volume in the same ratio, so each cubic centimeter still has a mass of 8 g.
- C Density belongs to the material, so the filing and the girder are both 8 g/cm³.
A plastic bead is less dense than water. What does the bead do in water?
- A It floats.
- B It sinks.
Answer
Key: A — It floats.
The bead is less dense than water, so it floats.
Feedback per option
- A An object less dense than the liquid floats.
- B An object denser than the liquid sinks; this bead is less dense than the water.
What to judge
Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?
8/10 on:
- Clear and concise language
- Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
- No "clangers" (content that causes a problematic misconception)
- Appropriate questions
- Initial testing
- Expansion into harder questions (no exam)
- The tasks should use similar language to that of the lesson
Gut check: better than the alternative? Would a student benefit? Full criteria
Applied without asking
Rulings you have already given; in force on every card above, not re-asked.
- Every video ends “Okay, now your turn.” with one easy, video-dependent question (the XP gate).
- An intro video is at most 120 words and teaches nothing: it opens the question the topic answers.
- A summary video is at most 300 words: everything taught, in order, just before the PP100.
- A lesson script is at most 200 words.
- Each lesson ships as both a video and an article; the article is not under review here.
The topic’s fixed wording (the lexicon the scripts repeat)
- Volume of the solid equals end reading minus start reading.
- Density is how much mass a material packs into each cubic centimeter.
- Density equals mass divided by volume, in grams per cubic centimeter (g/cm³).
- An object denser than the liquid sinks. An object less dense than the liquid floats.
- Density belongs to the material, not to the size of the piece.
Scripts, questions and quizzes are read from the course content as it stands today; the student site for this topic is here.