Question

Explain what is meant by the term mechanical advantage.

Answer 1

So, in general, we can push something with 10 N of force and it will usually experience a force of 10 N. But if we use levers and other mechanisms, we can magnify the force that is felt. For example, if there is the tendency to rotate, we can have that in the picture I have attached there is balance. That is because the torques have to be equal and this happens if the heavier object is much further from the support than the lighter one. This is the same mechanism as with doors; it is much easier to open a door from the handle than from the rim. At the handle, the torque is greater, even though the force you apply on both cases is the same. In this picture, while the force on the right is bigger, the torques get balanced due to the distance difference. Hence, you can apply 10N on the left side and you will be lifting a box that weighs 100N! That is the magic of levers and in scientific language it is called the mechanical advantage.

Answer 2

The term mechanical advantage is used to described how effectively a simple machine works. Mechanical advantage is defined as the resistance force moved divided by the effort force used. In the lever example above, for example, a person pushing with a force of 30 lb (13.5 kg) was able to move an object that weighed 180 lb (81 kg). So the mechanical advantage of the lever in that example was 180 lb divided by 30 lb, or 6. The mechanical advantage described here is really the theoretical mechanical advantage of a machine. In actual practice, the mechanical advantage is always less than what a person might calculate. The main reason for this difference is resistance. When a person does work with a machine, there is always some resistance to that work. For example, you can calculate the theoretical mechanical advantage of a screw (a kind of simple machine) that is being forced into a piece of wood by a screwdriver. The actual mechanical advantage is much less than what is calculated because friction must be overcome in driving the screw into the wood.

Sometimes the mechanical advantage of a machine is less than one. That is, a person has to put in more force than the machine can move. Class three levers are examples of such machines. A person exerts more force on a class three lever than the lever can move. The purpose of a class three lever, therefore, is not to magnify the amount of force that can be moved, but to magnify the distance the force is being moved. As an example of this kind of lever, imagine a person who is fishing with a long fishing rod. The person will exert a much larger force to take a fish out of the water than the fish itself weighs. The advantage of the fishing pole, however, is that it moves the fish a large distance, from the water to the boat or the shore.