Pressure: force and contact area
Stand bricks on a foam block on their flat side, their long side and their end, and see how the contact area and the force change the pressure.
Core concept
Pressure = force ÷ area: a smaller area or a bigger force gives a bigger pressure
Topic: Pressure
pressure: How much force presses on an area. A sharp knife has high pressure at its edge. All key words tells us how concentrated a force: A push or a pull. Forces can start, stop or turn things. All key words is: pressure = force ÷ area. It is measured in pascals (Pa); 1 Pa is a force of 1 N spread over 1 m². The same brick presses harder on the ground when it stands on its small end than when it lies flat, because its weight: The pull of gravity on something, measured in newtons. It is less on the Moon. All key words is spread over a smaller area. That is why knives are sharp, nails are pointed, and tractors and snowshoes have wide bases.
What you will learn
- Calculate pressure using pressure = force ÷ area.
- Show that a smaller contact area gives a greater pressure.
- Explain everyday examples of high and low pressure.
Before you start
- Know that weight is a force measured in newtons.
- Calculate the area of a rectangle.
Materials
- Bricks measuring 20 cm × 10 cm × 5 cm (25 N each)
- A thick foam block or a tray of damp sand
Equipment
- Ruler to measure the dent
Procedure
- Stand one brick on its flat side, its long side and its end, recording each time.
- Stack a second brick on top and record again.
- Compare how deep the foam is pressed in.
How this simulation is simplified
- Each brick weighs 25 N.
- The foam is pressed in 1 mm for every 500 Pa.