Pressure, Winds, Storms, and Cyclones
Measuring pressure, and why a sharp edge does the work
Learn how pressure is measured, and why a sharp knife cuts better than a blunt one.
Pressure is force per unit area, so its unit is made from the units of force and area:
| Quantity | SI unit |
|---|---|
| force | newton (N) |
| area | metre squared (m²) |
| pressure | newton per metre squared (N/m²), also called the pascal (Pa) |
A worked example. A force of 100 N pushes on a piece of cardboard of area 2 m². Pressure = 100 N ÷ 2 m² = 50 N/m², which is 50 Pa.
Try two jobs two ways (Table 6.1, with an adult watching):
| Job | Way 1 | Way 2 |
|---|---|---|
| drive an iron nail into wood | by its head | by its pointed end |
| cut an apple | with the sharp edge of the knife | with the blunt edge |
For each, write whether it was easy or hard, and why.
Both give the same answer. The pointed end of a nail and the sharp edge of a knife touch only a tiny area, so the same push makes a much higher pressure. That's why the nail goes in and the apple cuts.
So: a smaller area gives a higher pressure, and that makes some jobs much easier.
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