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Air has mass and takes up space: the particle model explains a pumped ball, a dry cup and a spreading smell.
Paper packet. Every task here also exists on screen, where it is checked automatically; answers written on paper are not assessed by Nydus. When you are back at a device, enter your answers there.
You will show that air is matter by working out the mass of air in a ball or balloon, and use particles too small to see to explain what you observe.
You know from the last lesson that mass is conserved: when sugar dissolves, every gram stays in the glass, even though you cannot see it. You can weigh things in grams and take one mass from another.
This lesson asks the question that lesson left open. If you cannot see the sugar, what is it made of that lets it hide and still weigh the same?
| Term | What it means |
|---|---|
| Matter | Anything that has mass and takes up space. |
| Particle | A piece of matter far too small to see, even with a magnifying glass. |
| Air | A mixture of gases all around us; it is matter made of particles. |
| Gas | Matter whose particles are spread far apart and move freely. |
| Evidence | Something you can observe or measure that supports an idea. |
| Model | A way of picturing something too small or too big to see directly. |
| Pressure | The push of particles hitting the inside of a container. |
All matter is made of particles far too small to see. You cannot see one, or even a thousand, but together they make up everything: your desk, the water in your glass, and the air you breathe.
The particle model explains three things you can observe:
In a gas like air, the particles are spread very far apart. That is why air is invisible and light, but it is still matter.
Another way: action
Blow up a balloon and hold it shut. Squeeze it gently. The push you feel back is billions of air particles hitting the inside of the rubber.
Another way: steps
Air is the hardest matter to believe in, because you cannot see it, and most of the time you cannot feel it either. But it passes both tests for matter.
It has mass. A flat soccer ball weighs about $410$ g. Pump it up hard and it weighs about $413$ g. Those three extra grams are air: the only thing you added.
It takes up space. Push an upside-down cup straight down into a bowl of water. The inside stays dry, because the cup is full of air and the water cannot get in until the air gets out. Tip the cup and a bubble escapes, and only then does the water rush in to take its place.
Nobody in your class can see a particle, so why should we believe in them? Because the model explains measurements that no other idea explains as well.
If air were nothing, a pumped ball would weigh the same as a flat one. It does not. If dissolved sugar were destroyed, sweet water would weigh the same as plain water. It does not. If a smell were not made of moving pieces, it could not travel from the kitchen to your bedroom. It does.
Scientists call an idea like this a model. A good model is not a guess. It is a picture that explains many observations at once and predicts new ones correctly. The particle model has passed every test for over two hundred years.
The same particle model explains why the three states of matter behave so differently.
That last point is why you can pump more and more air into a ball. You are pushing the spread-out particles closer together, packing extra mass into the same space.
Every weighing question in this lesson follows one short method. Take this one: an empty balloon weighs $5$ g, and blown up it weighs $7$ g.
A real balloon holds less air than that, because your breath is not packed in tightly, so a careful scale is needed. The idea is the same at any size.
Squeeze a flat ball and your thumb sinks in. Squeeze a pumped one and it pushes back. Nothing about the rubber changed, so what is pushing?
The answer is the air particles inside. They are always moving, and every moment billions of them hit the inside of the ball and bounce off. Each hit is a tiny push. One particle's push is far too small to feel, but together they add up to a strong, steady push on every part of the rubber. Scientists call that push pressure.
Pumping in more air puts more particles in the same space, so more of them hit the rubber each second and the push gets stronger. Let air out and there are fewer hits, so the ball goes soft. The particle model explains the feel of the ball and its weight with one idea.
Big containers, like a scuba tank or a propane tank for a grill, are weighed in kilograms. The method is the same, with one extra step at the end if the question asks for grams.
Say an empty tank weighs $14$ kg and a full one weighs $17$ kg.
The subtraction never changes. What changes is how tightly the particles have been packed, which is why the same method gives three grams for a ball and three thousand for a tank.
Run three checks.
The first check catches the most common slip: taking the pumped mass away from the flat one instead of the other way round.
The third check matters as much as the arithmetic. A number on its own only says that something got heavier. The particle model says why: tiny pieces of matter, too small to see, were pushed in, and each one brought its own tiny mass. When your answer names the particles and what they did, you have used the model, not just a subtraction. Try it with every observation in this lesson: the dry cup, the soft tire, the smell from the kitchen, and the sweet water where the sugar vanished. Each one is explained by particles that have mass, take up space and keep moving.
Official basketballs must be pumped to the right pressure. Too little air and the ball bounces flat; too much and it is hard to control. Referees check each ball with a gauge before a game.
The gauge measures how hard the air particles push on the inside of the ball. Pumping in more air packs more particles into the same space, so they hit the inside more often and push harder. A basketball pumped to game pressure holds about $6$ g of air, and those few grams are the difference between a ball that bounces to your waist and one that barely leaves the floor. Players can feel that difference the moment they dribble a ball.
So the bounce you feel on the court comes from billions of particles you will never see.
A diver's air tank is a strong metal bottle. At a dive shop it is weighed empty and then filled with air squeezed in by a powerful pump. A full tank can weigh about $3$ kg more than the same tank empty. That is $3{,}000$ g of air.
The tank can hold so much because gas particles are far apart and can be pushed much closer together, far closer than in the air around you, where the particles have plenty of room between them. As the diver breathes, the tank slowly gets lighter, and dive instructors teach new divers to expect this and adjust their weights so they do not float up at the end of a dive.
Every breath the diver takes is matter leaving the tank, with a mass you can weigh.
The most common idea is that air is nothing, so an "empty" bottle or a flat ball has nothing in it. A bottle with no liquid in it is full of air, and air has mass.
A second mistake is thinking air has no weight at all. It is light, because its particles are spread far apart, but a pumped ball is measurably heavier than a flat one.
A third is thinking air gets used up or disappears. When a tire goes flat, the air particles have left through a hole. They are still matter, now somewhere else.
Weigh the flat ball.
$410\ \text{g}$
No air pumped in.
Pump it up hard.
$\text{only air is added}$
Nothing else goes in.
Weigh it again.
$413\ \text{g}$
Heavier than before.
Subtract the flat mass.
$413 - 410 = 3\ \text{g}$
The air.
Say what it shows.
$\text{air has mass}$
So air is matter.
Turn a cup upside down.
$\text{full of air}$
It looks empty.
Push it straight into water.
$\text{water stays out}$
The inside stays dry.
Ask what stops the water.
$\text{air in the cup}$
The air particles fill the space.
Tip the cup slightly.
$\text{a bubble escapes}$
Air leaves as a bubble.
Watch the water level.
$\text{water rises inside}$
It takes the space the air left.
State the idea.
$\text{particles take up space}$
Even the invisible ones.
Open a jar of vanilla.
$\text{at one side of the room}$
The smell starts in the jar.
Wait a minute.
$\text{smell reaches the far side}$
Someone across the room notices.
Ask what traveled.
$\text{vanilla particles}$
Tiny pieces of the vanilla.
Ask how they traveled.
$\text{they keep moving}$
Bumping through the air particles.
Check the jar.
$\text{a tiny bit lighter}$
Some particles left it.
Ask why nobody saw them.
$\text{too small to see}$
Only noses detect them.
State the idea.
$\text{particles move and spread}$
That is how smells travel.
Read the full mass.
$6\ \text{g}$
Rubber and air.
Read the empty mass.
Subtract the empty mass.
A friend says an empty bottle has nothing in it. Is that true?
Complete the worked solution: a ball has a mass of $450$ g flat and $453$ g pumped up. A second ball has a mass of $110$ g flat and picks up the same mass of air. Find the air, then the second ball's pumped mass.
Find the air in the first ball.
$453 - 450 =$ a g
Only air was added.
Add it to the second ball.
$110 +$ b g
The same mass of air goes in.
Write the second ball's pumped mass.
$\text{pumped mass} =$ c g
Its flat mass plus its air.
Match each observation to the idea about particles that explains it.
| particles have mass | particles take up space | particles keep moving and spread out | particles are too small to see | |
|---|---|---|---|---|
| a pumped-up ball weighs more than a flat one | ||||
| you cannot push a sealed syringe of air all the way in | ||||
| you smell baking bread from the next room | ||||
| sugar vanishes in water but the water tastes sweet |
An empty balloon has a mass of $6$ g. Blown up and tied, it has a mass of $7$ g on a very careful scale. What is the mass of the air inside?
Answer: unit: g / kg
A flat ball has a mass of $410$ g. Each pump pushes in the same amount of air. After some pumps the ball weighs $412$ g. What is the total mass of air pumped in?
Answer: unit: g / kg
A student weighs a basketball with no air in it: $600$ g. They pump it up hard and weigh it again: $606$ g. What mass of air did they pump into the ball?
Answer: unit: g / kg
A friend says an empty bottle has nothing in it. Is that true?
A dive shop weighs an empty scuba tank: $15$ kg. A pump squeezes air into it until it weighs $17$ kg. How many grams of air are in the full tank?
Answer: unit: g / kg
Lesson test: one question per skill, one attempt each, no hints. Your answers are checked when you submit.
An empty balloon has a mass of $5$ g. Blown up and tied, it has a mass of $8$ g on a very careful scale. What is the mass of the air inside?
Answer: unit: g / kg
You can use the particle model. Tell someone why a flat ball weighs less than a pumped one.
18. Your turn: an empty balloon weighs 4 g. Blown up, it weighs 6 g. What is the air's mass?, step 2
$4\ \text{g}$
Rubber alone.
18. Your turn: an empty balloon weighs 4 g. Blown up, it weighs 6 g. What is the air's mass?, step 3
$6 - 4 = 2\ \text{g}$
The mass of the air.