Pressure on solids – snowshoes, skis, stiletto heels, drawing pins and bricks
Integrated ScienceForces & MotionAges 13–14
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Stand a person in boots, on snowshoes, on skis or in stiletto heels, an elephant, or push a drawing pin onto snow, sand or a wooden board. Change the force F and the contact area A to read the pressure p = F/A in pascals and measure how far the object sinks on the ruler. The Brick screen rests the same brick (or a stack of bricks) on each of its three faces and records the pressures in a table to compare them.
Lesson: Pressure on a surface: force, contact area, p = F/A, the pascal; increasing and reducing pressure
What it shows
Pressure tells us how concentrated a force is: it is the force acting at right angles to a surface divided by the area it acts on, p = F/A, measured in pascals (1 Pa = 1 N/m²). The same weight spread over a large area, as with snowshoes or skis, gives a small pressure, so you hardly sink into snow. Concentrated on a tiny area, as with a stiletto heel or the point of a drawing pin, it gives an enormous pressure that pushes into sand or wood. A brick resting on its smallest face presses hardest on the ground.
How to use
On Sinking test, choose an Object and a Surface, then change Force F and Contact area A with the sliders (each object starts at typical values) and press Put down. Read the pressure and the depth, then press Record to add the trial to the table and the graph. On Brick, choose the Face down and the Number of bricks, press Put down and record each face to compare the pressures.
Parameters you can change
- Screen Sinking test, Brick
- Object Person in boots, Person on snowshoes, Person on skis, Person in stiletto heels, Elephant, Drawing pin
- Surface Snow, Sand, Wooden board
- Force F 1–60000 N
- Contact area A 0.001–5000 cm²
- Face down Large face, Side face, End face
- Number of bricks in the stack 1–4
Questions to explore
- Why do snowshoes stop you sinking into snow even though your weight stays the same?
- Which face of a brick should rest on soft ground to give the least pressure?
- Why does a drawing pin have a broad head but a sharp point?
