Distinguish between mass and weight - Junior Cycle Science - Question a (i) - 2013

The moment of a force is defined as the product of the force and the distance from the point of rotation (lever arm). It can be expressed mathematically as:

$ext{Moment} = ext{Force} imes ext{Distance}$

To find force F, we can use the principle of moments. Since the metre stick is balanced, the clockwise moments must equal the counterclockwise moments. The moment created by the 4 N force is:

$ext{Moment}_{4N} = 4 ext{ N} imes 30 ext{ cm} = 120 ext{ N cm}$

The moment created by the force F at the 70 cm mark is:

$ext{Moment}_{F} = F imes 20 ext{ cm}$

Setting these equal gives:

$120 ext{ N cm} = F imes 20 ext{ cm}$

To solve for F, divide both sides by 20 cm:

$F = \frac{120 ext{ N cm}}{20 ext{ cm}} = 6 ext{ N}$

Thus, the force F is 6 N.

One common application of levers is a door handle. When you push or pull on the handle, it acts as a lever to make it easier to open or close the door.