Unit 4 - Forces, density and pressure

The turning effect of a force

Also called the moment, which is the **product** of the **force** multiplied by **the perpendicular distance** from the line of action of the force to the pivot or point where the object will turn.

Couple definition

consists of two forces, equal in magnitude but opposite in direction whose lines of action do not coincide.

Torque of a couple

The principle of moments

for an object to be in rotational equilibrium, the sum of the clockwise moments about any point must equal the sum of the anticlockwise moments about that same point.

Conditions of equilibrium

1 the sum of the forces in any direction must be zero
2 the sum of the moments of the forces about any point must
be zero.

Density

Pressure

Pressure in a liquid

Formula if the pressure in a liquid increases

the change in pressure in a fluid, Δp due to the change in depth Δh is given by:

What is a Manometer and what is a Barometer?

Manometer - pressure measuring device which measures the difference of pressures in two tubes.

Barometer - pressure measuring device which measures the atmospheric pressure.

Archimedes’ principle (upthrust)