Pressure
1. What is Pressure?
Pressure is the amount of force applied per unit area.
Formula:
Force
Pressure = -------------------
Area
Simple example:
A sharp knife cuts easily → small area → high pressure
A blunt knife doesn’t → large area → low pressure
2. Why Pressure Exists
Pressure exists because:
Objects have weight (gravity pulls them down)
Particles (atoms/molecules) collide with surfaces
Fluids (liquids & gases) can flow and push in all directions
3. Pressure in Solids
In solids, pressure depends on:
Force applied
Area of contact
Examples:
High-heeled shoes sink into soft ground (small area → high pressure)
Snowshoes prevent sinking (large area → low pressure)
Nails have sharp tips to increase pressure
4. Pressure in Liquids
Liquids exert pressure due to their weight.
Important facts:
Liquid pressure increases with depth
It does not depend on shape of container
Pressure acts in all directions
Formula:
P=hρg
Where:
h = depth
ρ = density
g = gravity
Examples:
Examples:
Dam walls are thicker at the bottom
Ears hurt when diving deep underwater
Water jets out farther from lower holes in a tank
5. Pressure in Gases (Gas Pressure)
Gas pressure is caused by collisions of gas molecules with container walls.
Factors affecting gas pressure:
Temperature ↑ → pressure ↑
Volume ↓ → pressure ↑
Number of gas molecules ↑ → pressure ↑
Examples:
Inflated balloon becomes tight
Heated gas expands
Tyres burst in extreme heat
6. Atmospheric Pressure
Atmospheric pressure is the pressure exerted by the air around Earth.
At sea level:
≈101,325 Pa\approx 101{,}325 \text{ Pa}≈101,325 Pa
Key points:
Air has mass → it exerts pressure
Pressure decreases with altitude
Examples:
Drinking with a straw
Suction cups sticking to walls
Difficulty breathing at high mountains
7. High Pressure and Low Pressure (Physics & Weather)
High Pressure
Particles are closely packed
More force per area
Air sinks (in atmosphere)
Results:
Clear skies
Calm weather
Dense air
Low Pressure
Particles are far apart
Less force per area
Air rises
Results:
Clouds
Rain
Storms
8. Pressure Difference
Pressure difference causes motion
Things move from:
High pressure → Low pressure
Examples:
Wind flows due to pressure difference
Blood flows due to pressure difference
Air rushes out of a punctured tyre
9. Applications of Pressure
Daily Life
Syringes
Hydraulic brakes
Vacuum cleaners
Pressure cookers
Technology
Hydraulic lifts (Pascal’s Law)
Barometers (measure pressure)
Scuba diving equipment
10. Pascal’s Law
Pressure applied to an enclosed fluid is transmitted equally in all directions.
Used in:
Hydraulic press
Car lifts
Braking systems
11. Units of Pressure
Pascal (Pa)
Atmosphere (atm)
Bar
mmHg (mercury)
PSI (pounds per square inch)
12. Summary
Pressure = force ÷ area
Smaller area → more pressure
Liquid pressure increases with depth
Gas pressure comes from molecular collisions
Atmospheric pressure decreases with height
Motion happens due to pressure difference