Mass is how much matter there is in something — how many particles, in effect. It is measured on a balance in grams, and it does not change if you move the object, squash it or take it to the Moon.
Mass How much matter something contains.
Step 1: Something to Notice
Watch first. The explanation comes later.
A huge block of polystyrene packaging and a small lump of lead. The polystyrene is twenty times the size and a fraction of the weight.
Does taking up more space mean having more matter?
Step 2: Find Out
Watch what the particles do without any of them being added or removed.
Step 1 — Predict
The particles spread out to fill the whole jar. What happens to the mass?
Choose what you think will happen. You cannot see the experiment until you do — guessing first is what makes it worth watching.
Step 3: So Here Is Why
Now the explanation, after you have seen it happen.
Volume is how much space
Volume is the amount of space something takes up. You can measure it by how much water it pushes aside.
Volume The amount of space something takes up.
They are separate
The gas in the jar took up the whole space and weighed exactly what the solid did.
Together they give density
Density is mass divided by volume: how much matter is packed into each unit of space. It is the reason a small lump of lead outweighs a large block of foam, and the reason a heavy-looking thing can float while a small pebble sinks.
Two different questions
Volume is how much space something takes up; mass is how much matter is in it. A large polystyrene block has big volume and small mass. Confusing the two is behind most density confusion.
density How heavy something is for its size.
Density combines them
Density is mass divided by volume, so it says how tightly packed the matter is. It explains why a small stone sinks and a large log floats, which size alone cannot.
Step 4: A Common Mistake
Lots of people think
“Bigger things are heavier.”
Step 5: Why Some Things Float
The same idea somewhere new.
Mass divided by volume is called density, and it decides whether something floats. A steel ship floats because most of what you are weighing is the air inside it — the steel and the air together are less dense than water, even though steel alone sinks instantly.
Step 6: Think It Through
Practice makes it stick.
The Measuring Jug
Problem 1 of 2
Water is at 200 ml. With the stone in, it reads 260 ml. What is the stone’s volume?
ml
Big and Light
Problem 2 of 2
A huge block of foam weighs less than a small lump of lead. What does that show?
Mass and Volume
1 of 4
What is mass?
2 of 4
What is volume?
3 of 4
The particles spread out to fill the jar. What does the balance read?
grams
4 of 4
Are bigger things always heavier?
Step 7: Quick Check
Show what you know.
Question 1 of 1
The particles spread out and take up much more space. What happens to the mass?
Step 8: Explain It in Writing
Claim, evidence, then reasoning.
The question
Somebody says bigger things are heavier. Using what the particles and the balance did, write an argument saying whether taking up more space means having more matter.
Evidence you can use
- When the particles spread out, they filled far more of the jar.
- The balance read exactly the same before and after they spread out.
- No particles were added and none were taken away.
- A block of polystyrene can be twenty times the size of a lump of lead and weigh far less.
- Mass divided by volume is density, and density is what decides floating.
- A steel ship floats because most of what you are weighing is the air inside it.
Words to usemassvolumematterspaceparticlesdensity
Fill in all three boxes. The reasoning box is the one that matters most.
What You Found Out
- Mass is how much matter something contains.
- Volume is how much space it takes up.
- They are separate — spreading out changes volume and not mass.
- Mass divided by volume is density, which decides whether something floats.