Keshu

1. What is Pressure?

Pressure means force applied on a surface.

FORCE

Pressure= -----------

AREA

• Same force on smaller area → more pressure

• Same force on bigger area → less pressure

Example:

• A sharp knife cuts easily because force is on a very small area.

• Snow shoes stop you from sinking because force is spread over a large area.

2. Pressure in Gases

Gases (like air) are made of tiny particles moving freely and fast.

How gas pressure is produced:

• Gas particles move randomly

• They collide with the walls of a container

• Each collision applies a tiny force

• Millions of collisions create gas pressure

Important points:

• More particles → more pressure

• Higher temperature → particles move faster → more pressure

• Smaller container → more collisions → more pressure

Example:

• Pumping air into a bicycle tire increases pressure

• Heating a sealed gas container increases pressure

3. Atmospheric Pressure

The Earth is surrounded by air called the atmosphere.

Why atmospheric pressure exists:

• Air has mass

• Gravity pulls air downward

• The weight of air presses on everything

This pressure is called atmospheric pressure.

Key facts:

• We don’t feel crushed because pressure inside our body balances it

• Atmospheric pressure decreases with height

  • High mountains → lower pressure

  • Sea level → higher pressure

Example:

• Ears popping when going up a mountain or in an airplane

4. Pressure in Liquids

Liquids also create pressure due to their weight.

Important rule:

Pressure in a liquid increases with depth

That means:

• Shallow water → less pressure

• Deep water → more pressure

This pressure acts:

• In all directions

• On the bottom and sides of the container

5. Pressure in Water

Water pressure depends on three main factors:

1. Depth (Most Important)

• More depth → more water above you → more weight → more pressure

Formula idea

Pressure=ρgh

where:

• ρ= density of water

• g = gravity

• h = depth

2. Density of the Liquid

• Water creates more pressure than oil at the same depth

• Denser liquids → more pressure

3. Gravity

• Stronger gravity → more pressure (important in planets)

Real-life examples:

• Dams are thicker at the bottom

• Divers feel ear pain as they go deeper

• Submarines need strong walls

Important note:

Water pressure does not depend on:

• Shape of the container

• Amount of water (only depth matters)

6. Particles and Pressure (Microscopic View)

Now let’s connect pressure to particles.

In gases:

• Particles move fast

• Pressure comes from collisions with surfaces

More collisions → more pressure

In liquids:

• Particles are closer together

• They move less freely than gas

• Pressure is mainly due to weight of particles above