6.17Chapter 6: Forces, Motion and Pressure

Pressure in gases — Alhussan Physics - Stage 8 Revision Notes & Topical Questions

5 min read 8 parts Lesson 17 of 19 2 quizzes

📚 Alhussan Physics - Stage 8 Hub / Topical Revision

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Physics 6.17 Pressure in gases — Particle Collisions and Atmospheric Pressure — Alhussan International Academy — Physics (Stages 7–9) notes: Explain gas pressure using particles and describe the factors that affect gas pressure and atmospheric pressure.Particle model — The partic…

Cause of pressure
Adding more gas
Smaller volume
Higher temperature
Oxygen tanks
Reason for compression

Section 1 of 8Gas pressure and particles

Gas pressure and particles

Particle model

The particles in a gas are far apart, moving fast in random directions.

Cause of pressure

Gas particles bump into each other and into the walls of their container.
The collisions with the walls produce gas pressure.
All gases, including gases inside you, exert a pressure on the walls of their container.

Balloon

Air particles hit the inside and outside of the balloon, and more collisions on the inside make it bigger.

Section 2 of 8Factors affecting gas pressure

Adding more gas

More particles mean more collisions with the walls, so the pressure increases.
In a container of fixed shape the pressure rises as air is pumped in.
Too much gas can make a balloon burst.

Smaller volume

The same particles in a smaller volume collide with the walls more often, so the pressure is higher.

Higher temperature

Particles move faster, so there are more and harder collisions and the pressure is higher.

Section 3 of 8Atmospheric pressure

Atmospheric pressure

Atmospheric pressure the pressure of the air around us, caused by air particles colliding with surfaces.

We do not feel it because it is balanced by the pressure of gases and liquids in our bodies pushing outwards.

Height

Atmospheric pressure at sea level is bigger than high up a mountain.
Gravity pulls air particles towards the Earth, so the air near the surface is compressed.
Closer particles mean more collisions and a bigger force.
Higher up there is less air above, so fewer particles and fewer collisions.

Effects

Marshmallows contain air pockets that expand when the air around them is pumped out,
because outside pressure falls while inside pressure stays the same.

Section 4 of 8Compressed gases

Oxygen tanks

Firefighters and people in places with low oxygen use tanks of oxygen compressed into a small volume.

Reason for compression

Otherwise they could not carry enough oxygen.

High pressure

The pressure inside is very high, so the tanks are made of metal that can withstand it.

Release

Gas flows out of the valve because its pressure is higher than the atmospheric pressure outside.

Section 5 of 8Comparing gases and liquids

Property	Gas	Liquid
Particle spacing	Far apart	Touching
Compressible	Yes, easily	Almost not at all
Cause of pressure	Collisions with walls	Collisions and the weight of liquid above

Section 6 of 8Everyday gas pressure

1Bicycle tyre

Pumping adds more air particles into a fixed volume, so collisions with the inner wall increase.

2Sealed crisp packet

At altitude the outside pressure falls but the trapped gas pressure stays the same, so the packet swells.

3Drinking straw

Sucking lowers the pressure inside the straw, and the greater atmospheric pressure pushes liquid up.

Section 7 of 8Key terms

Term	Meaning
Gas pressure	The pressure caused by gas particles colliding with a surface.
Atmospheric pressure	The pressure of the air above a surface.
Compress	To squeeze into a smaller volume.
Particle model	A model in which matter is made of moving particles.
Collision	When particles hit each other or a surface.