Pressure & Forces Flashcards

All 7 cards in this deck

In which direction does the pressure in a fluid act on a surface?

It produces a force acting normal (at right angles) to the surface.

What is the equation linking pressure, force and area?

$\text{pressure} = \dfrac{\text{force normal to surface}}{\text{area of that surface}}$, i.e. $P = \dfrac{F}{A}$

What are the units of pressure, force and area in $P = F \div A$?

Pressure in pascals (Pa), force in newtons (N), area in metres squared (m$^2$).

What are the steps to calculate pressure from a force and an area given in cm²?

e.g. a force of $60$ N normal to an area of $200$ cm²

1. Convert the area to m$^2$ by dividing by $10\,000$: $200 \div 10\,000 = 0.02$ m$^2$
2. Divide force by area: $P = 60 \div 0.02$
3. Pressure $= 3000$ Pa

Why does a sharp blade cut more easily than a blunt one for the same force?

Its smaller contact area gives a much greater pressure, since $P = F \div A$.

In a hydraulic system, why is the output force on the wide piston larger than the input force on the narrow piston?

The pressure in the oil is the same throughout, and the wide piston has a larger area, so $F = P \times A$ is greater.

True or false? Snowshoes stop a walker sinking into snow because they reduce the walker's weight.

False. They increase the contact area, which reduces the pressure on the snow; the weight is unchanged.