CIE iGCSE Co-ordinated Sciences-P1.7 Pressure- Study Notes- New Syllabus

Pressure and Its Variation with Force and Area

What is pressure?

Pressure tells us how strongly a force is acting on a surface. It is not only about how big the force is, but also about how that force is spread out.

Effect of Force:

If you press harder with your hand on a table, the force increases. 

• A larger force on the same area produces a larger pressure. 
• Everyday link: A heavy box creates more pressure on the floor than a light box of the same size.

Effect of Area:

• The same force can feel very different if spread over a large area or concentrated in a small area.
• A smaller area concentrates the force, producing a higher pressure. 
• A larger area spreads the force, producing a lower pressure. 
• Everyday link: A drawing pin is designed with a wide head (so it doesn’t hurt your finger) and a sharp tip (to easily pierce the surface).

Key idea:

High pressure = large force on small area.

Low pressure = force spread over a large area.

Concept-Building Everyday Examples:

High-heeled shoes vs. flat shoes:

A person’s weight is the same in both cases. But high heels concentrate this weight on a tiny heel tip, creating very high pressure that can dent wooden floors or sink into soft ground. Flat shoes spread the same weight over a larger area, producing much lower pressure.

Snowshoes vs. normal shoes:

In snow, normal shoes sink because the force (body weight) acts on a small area, producing high pressure. Snowshoes have wide surfaces that spread the weight over a large area, reducing pressure and preventing sinking.

Sharp knife vs. blunt knife:

Both may apply the same force from your hand. The sharp knife has a much smaller contact area at the edge, so it produces a much higher pressure, cutting easily. A blunt knife has a wider edge, lowering the pressure, and so struggles to cut.

Elephant’s foot vs. camel’s foot:

An elephant is very heavy, but its large, broad feet spread its weight, reducing pressure so it does not sink into soft mud. Camels have wide feet that reduce pressure on desert sand, preventing them from sinking.

Drawing pin:

The flat head distributes the force of your finger over a wide area (low pressure, so it doesn’t hurt). The sharp tip concentrates the same force on a tiny area (high pressure, so it easily pierces wood or paper).

In summary:  Pressure depends on both the force and the area. Everyday experiences (like shoes, knives, pins, or animals’ feet) show how increasing force or decreasing area increases pressure, while decreasing force or increasing area decreases pressure.