the lever
the lever
Your arm can be considered a first class lever.
What the most useful machine is, is a matter of opinion. Some would argue that the wheel is the most useful machine, and others would argue that the lever is the most useful.
Page 223 of your science book
A pencil isn't a lever at all, unless you are using it to turn force into useful motion. If you use the pencil to write with, it's closer to being a needle reading a record, as it is dragged across a surface, leaving graphite which has broken off of the main core on the paper. For a first class lever, think of a see-saw. For a second class lever, think of a wheelbarrow. For a third class, think of a pair of nail clippers, or of your forearm.
A foot lever is a lever that is operated with the foot.
The function of a lever is used to move or lift objects.
A fulcrum in a lever is very important because without a fulcrum a lever isn't a lever , and the fulcrum is the main part of a lever.
The third class lever is the most common lever in the body.
3rd class lever
Class 1 lever