Levers

Pushcarts - Levers

How has it been done before?

Engineering Facts

Levers are mechanisms that can swivel or tip on a fixed point called a fulcrum. A see-saw is a lever. The fulcrum is in the middle of the see-saw and the people at each end can go up and down.

In some levers the fulcrum is not in the centre but close to the end. A wheelbarrow has its fulcrum at the wheel which is at one end of the wheelbarrow.

For all levers, the force that makes it tip is called the effort. The thing that is being tipped is called the load.

There are three types of levers that are different in the order and direction of the load (L), effort (E) and fulcrum (F). The load is the weight we are trying to lift and the effort is the force we need to lift it. Whether we lift up or push down will depend on what we are trying to do. In the drawing opposite

the first two levers are the same type of lever (L F E - first order). The first one is like a see-saw and the second one is like when you use a crow-bar to lift a rock. We have to push down to lift the load.
the wheelbarrow is a different type (F L E - second order). We have to lift the handle to lift the load.
the fishing rod is different again (F E L - third order). We rest the rod against our body (the fulcrum) then lift the middle of the rod to lift the load (the fish on the line).

There are lots of levers on your pushcart:

your front axle must swivel around its attachment to the pushcart so that you can steer
your brakes and even your steering might work using lever mechanisms

Suggestions and Choices

When designing mechanisms that use levers your aim is to

minimise the effort needed to move the load when designing or choosing wheel size, steering mechanism, braking mechanism
maximise the effort needed to move the load when designing pushcart frame and pushbar

Try This

Investigate how levers work.

Investigate how your knowledge of levers can help when you design your steering mechanism. Levers can also be used for braking.

For Teachers

Multiplying the force by the distance from the pivot give us a measure of the mechanical energy (a combination of force and movement). By doing this we can calculate input to and output from the lever system (lever, nail, bags of washers on the load and effort sides of the ruler). The distances that the load and effort are placed on either side of the pivot are related to the movement part of the mechanical energy.

Levers and wheel-axle combinations are what engineers call simple machines. Simple machines take a given input of mechanical energy and output it as a different combination of force and movement.

If we want to produce a large force to push the front wheels of our pushcart sideways so that the cart can change direction (steer it), we can apply a smaller force (effort) to the steering handles and turn them a long way (say 200 mm). This will produce a large sideways force on the wheel arms to turn them, but they will only move 20 mm as they turn.

The see-saw is one example of a lever. Learn more about levers! Levers are important in the braking system and steering of the pushcart.

Support Materials developed by engineeringLinks at UTS

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