What is a tool that can be used to measure the size of a force

The answer to this question would be: a spring scale.

The spring scale that you use to determine your body weight is actually a device that measures your body gravitational force. The force itself influenced by your body weight, that is why it can determine your body weight.
More weight means more force, more force will shrink the spring more.

An atom that has fewer electrons that protons is called a positive ion.