# Properties of Force (by Mr. Coe's Class)

Force is difficult to define--the short definition from middle school days is "a push or a pull", which gives a very primitive understanding of a sophisticated concept. In physics, definitions are not sufficient--one grows to understand concepts by working with them, and understanding their properties.

Here is a list of properties of force developed by Mr. Coe's class (2009):

1. Force is a vector.

2. Force is measured (in SI units) in Newtons.

3. Force, when not balanced, can change the velocity of an object.

4. Forces are not visible.

5. When forces are balanced, an object is at rest or moving at constant velocity (in an inertial frame of reference).

6. Forces are interactions between objects, not "single," isolated entities. In other words, forces always come in pairs.

7. Force interactions are always equal in magnitude. In other words, the same size force acts on both objects in the interaction.

8. Force interactions always act in opposite directions on different objects.

9. Force interactions occur due to contact between objects or "at-a-distance" (field) interactions such as gravitational force.

10. If an object is observed to be at rest or moving at constant velocity in an inertial frame of reference the forces on it must be balanced (sum to zero as vectors).

11. Forces can be exerted by both animate and inanimate objects.

12. The relative magnitude of forces can be determined from using identical masses (or the same object) and measured accelerations when forces are applied.

13. Objects do not have to move to exert force.

14. Mathematically, force relates to acceleration and mass as follows: F = ma  or  $a=\frac{F}{m}$