Levers & Moments

Levers Forces can move objects by turning them around a pivot or fulcrum. A long bar that pivots is a lever. When you push down on one side, you are applying force. The object on the other end (the load) moves up. Using a lever magnifies the force and makes objects easier to move. Load moves up when force applied Force Load Pivot/Fulcrum

Types of Levers – First Order In this type of lever the pivot (or fulcrum) is between the effort and the load as in the simple crowbar.

Types of Levers – Second Order In this type of lever the load is between the effort and the pivot (or fulcrum) as in the wheelbarrow.

Types of Levers – Third Order In this type of lever effort is between the load and the pivot (or fulcrum) as in the pair of tweezers.

Task: Jenny is using a lever to lift this large box. 1. Label the diagram of this with the following key words: Load Pivot Force 2. Do you think it would be easier to lift the box with a shorter lever? Explain your answer.

As Jenny applies force to the lever, she exerts effort at one end. Task: As Jenny applies force to the lever, she exerts effort at one end. The effort (force downwards) causes the load on the other end of the lever to move upwards. Effort Load Pivot/Fulcrum

moment = force (N) x perpendicular distance from pivot (cm or m) Moments The moment or “turning effect“ can be calculated using the following equation: moment = force (N) x perpendicular distance from pivot (cm or m) moment f x d Moments are measured in Newton centimetres (N cm) or Newton metres (N m).

Calculate the moment: 10 cm 50 N cm 5 N pivot

Calculate the moment 5 cm 25 N cm 5 N pivot

Calculate the moment: 10 cm 100 N cm 10 N pivot

Calculate the force: 2 m Moment = 500 N m 250 N Force

Balanced Moments: 10 m 10 m 10 N 10 N pivot Left Moment Right Moment 100 N m 100 N m 10 N 10 N pivot

Balanced Moments: 10 m 7 m pivot 10 N 10 N Left Moment Right Moment 100 N m 70 N m pivot 10 N 10 N

Balanced Moments: 20 N 10 N pivot 10m 10 m Left Moment Right Moment 100Nm 200Nm 20 N 10 N pivot

Balanced Moments 10 m 5 m 10 m 20 N 10 N pivot Left Moment Right 100Nm 100Nm 20 N 10 N pivot

Principle of moments For an object to be in equilibrium (balanced), the following two conditions must be true: The total upward force is equal to the total downward force. The sum of the anticlockwise moments is equal to the sum of the clockwise moments

Calculate the load on each side and say if the level is balanced, will move clockwise, or will move anticlockwise. Balanced Will move anticlockwise Will move clockwise Will move anticlockwise

Question Why is it easier to open a tin of paint with a screw driver than with your bare hands?

Question Why is it easier to open a tin of paint with a screw driver than with your bare hands? The screwdriver acts as a first order lever. The pivot (fulcrum) is at the point where the effort is applied on the lid. By using a screwdriver, you increase the distance at which the effort is applied. This increases the moment, making it easier to open the lid.