1. ForcesForces

2. What is a force? A force is a push or a pull. Like velocity and acceleration, a force is described by it’s strength and by the direction in which it acts. Ex- if you push on a door, you are exerting a force on the door. The strength of a force is measured in the SI unit called newton (N)

3. Combining Forces The combination of all forces acting on an object is called the net force. When forces act in the same direction, the net force can be found by adding the strengths of the individual forces. 5N + 5N =10N

4. Combining Forces Forces may cancel each other out and produce no net force. If the white arrow is 5N and the blue arrow is 5N – since they are acting in opposite directions they cancel each other out. If the white arrow was 5N and the blue one was 10N then the net force would be 5N.

5. Unbalanced Forces Unbalanced forces can cause an object to start moving, stop moving, or change directions. Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion. Ex. A boy and a girl pushing on a box in opposite directions- the boy pushes with greater force- their forces are unbalanced and the net force acts on the box, causing it to move. (The net force on the box is the difference between their individual forces)

6. Balanced Forces Equal forces acting on an object in opposite directions are balanced forces. Each force is balanced by the other. Balanced forces acting on an object do not change the object’s motion. When equal forces are exerted in opposite directions, there is no net force. Ex. When two people push a box with equal force in opposite directions, the forces balance each other out. The box does not move.