B. FORCES

• The concept of force: force as a push or pull on an object
Examples of familiar forces (such as gravity, magnetic force)
A force has both direction and magnitude.
Measuring force: expressed in units of mass, pounds in English system, newtons in metric system

• Unbalanced forces cause changes in velocity.

If an object is subject to two or more forces at once, the effect is the net effect of all forces.

The motion of an object does not change if all the forces on it are in balance, having net effect of zero.

The motion of an object changes in speed or direction if the forces on it are unbalanced, having net effect other than zero.

To achieve a given change in the motion of an object, the greater the mass of the object, the greater the force required.