1. How can we describe how objects move?

2. The law of BALANCED FORCES  Objects at rest tend to stay at rest.  Objects in motion tend to stay in motion.  An object’s motion does not change if the forces do not change.  This is known as inertia.

4.  When you consider an object, think about the system of forces acting on it.  A force is a push or a pull acting on an object.  Don’t forget about gravity and friction!

5. The law of UNBALANCED FORCES  IF the forces acting on an object are unbalanced, the object’s motion (velocity) will change. (The object will accelerate.)  The change is in proportion to and in the same direction as the unbalanced force.

7.  Mathematically, f = ma  The unit for force is a newton.  N = kgm/s 2  Mass is a measure of inertia.  Weight is a measure of the force of gravity.

8. The law of ACTION AND REACTION  For every action there is an equal and opposite reaction.  Think of the objects and forces as a system.  Actions/reactions come in pairs. Their FORCES are equal and opposite, but the MASSES and ACCELERATIONS are not.  Remember, f = ma!

9.  f = ma (units are kgm/s 2 or N)  If two equal masses are acted on with different forces, the resulting accelerations will be in proportion to the forces. f f a a

10.  f = ma (units are kgm/s 2 or N)  If two masses are acted on with equal forces, the resulting acceleration will depend on each of their masses. f f a a