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Levers

A lever is a rigid bar that rotates around a fixed point. This balancing point is called the fulcrum. A lever uses a force (or effort) to make the load move.

There are different types of levers, depending on where the load, the effort, and the fulcrum (balancing point) are positioned. For this reason, levers are classified into 3 separate groups: Class 1, Class 2, and Class 3.

• Class 1 lever: This is where the fulcrum is between the load and the effort.

  One example would be using a screwdriver to open a can of paint (see Diagram 4). In this case, the screwdriver is the lever.

  Imagine how much harder it would be if you had to lift the lid off a paint can with your fingers, without the help of a lever!

  Pushing down on the lever (the screwdriver) raises the load (the paint can lid).

  

  Other examples of Class 1 levers include:

  • using a bottle opener to open a bottle of drink
  • using a claw hammer to pull out a nail
  • playing on a see-saw.

• Class 2 lever: This is where the fulcrum is at one end of the lever, the effort is at the other end, and the load is in between.

  One example would be a person lifting a load in a wheelbarrow (see Diagram 5). In this case, the wheelbarrow and its handles are the lever, the load is the weight in the wheelbarrow, and the force applied by the person lifting the handles is the effort. The fulcrum (the balance point of the lever) is the axle of the wheelbarrow.

  

  Other examples of Class 2 levers include:

  • staplers that staple sheets of paper together
  • nutcrackers that have the hinge at the end of the machine.

• Class 3 lever: This is where the fulcrum is at one end of the lever, the load is at the other end, and the effort is in between. These levers involve using a large effort to move a small load a long distance.

  An example is a person playing golf (see Diagram 6). In this case the golf club plus the person's arms is the lever, the golfer's shoulder is the fulcrum, the force being applied to the golf club by the golfer's hands is the effort, and the load is the weight of the golf ball.

  

  Other examples of Class 3 levers include:

  • using a cricket bat, a tennis racquet or a hockey stick to hit a ball
  • using a fishing rod to cast a fishing line.

  There are many levers in the Simple Machines Animation. How many can you spot?

Levers in balance

A see-saw is actually a lever with a fulcrum (balancing point) in the middle (see Diagram 7). Think about a see-saw with two people sitting at different distances from the fulcrum. If one person is twice as heavy as the other, the lighter person must sit further away from the fulcrum than the heavier person for the see-saw to be balanced.

Once balanced, it requires very little force for each person to push the see-saw up and down with their legs.