|A crowbar is an example of a lever.The effort is less than the load because the load is NEAR to the fulcrum and the effort is a long way from the fulcrum
Notice how the direction of the force can be represented by an arrow.
Other examples for the application of levers are: pliers, scissors, wheel barrow. These are all examples of simple MACHINES.
|Moment = force x distance
Where distance represents the distance of the force from the fulcrum.The unit of moment is a newton metre (Nm)
or newton centimetre (Ncm)Sum of moments on left of fulcrum = Sum of moments on right of fulcrum(or Anti-clockwise moments = Clockwise moments)
(Forces on opposite side of the fulcrum)Worked example
Imagine a ruler pivoted at the centre
If the ruler is balanced the lever law states that:
The force on the left x its distance from the pivot = the force on the right x its distance from the pivot
ie 2N x 6cm = 3N x 4cm
Forces on the same side of the fulcrum
A spring, attached to a ruler, balances a weight.
What force does the spring exert on the ruler?
The ruler exerts exactly the the same force on the spring, causing it to extend.
If we knew the original length of the spring we could calculate the extension caused by this force.
Experiment to stretch a spring
A spring is clamped near a metre rule.
1N weights are added to the spring, one at a time, and the total extension for the new load is recorded. A graph is drawn plotting extension against load.
Click on the image below to see a Hooke’s Law simulation ↓
Springs in series
Eg if one spring stretches 3cm with a load of 1N then two springs in series will stretch 6 cm. This is because each of the springs stretch 3cm making 6cm all together. If each spring were 10cm long to start (with no load) the total length would be 10cm + 10cm + 6cm = 26cm
Springs in parallel