Define the moment of a force - Leaving Cert Physics - Question a - 2006

One necessary condition for the crane to be in equilibrium is that the clockwise moments about the pivot must equal the anticlockwise moments. This ensures that there is no net moment acting on the crane.

The moment of the 9000 N concrete slab about the axis can be calculated as:

$ext{Moment} = ext{Force} imes ext{Distance} = 9000 ext{ N} imes 10 ext{ m} = 90000 ext{ Nm}$

Using the principle of moments, we can set the sum of clockwise moments equal to the sum of anticlockwise moments:

$90000 ext{ Nm} = X imes 30 ext{ m}$

Solving for X gives:

X = rac{90000 ext{ Nm}}{30 ext{ m}} = 3000 ext{ N}

Another example of a lever is a crowbar, which is used to lift heavy objects with less effort.