Students should know the overall effect of many forces acting on an object at the same time. The size and direction of this net force determines the change in motion of an object.

What causes an object to start moving, stop moving or change direction? A Force - a push or pull

What happens when two friends push on the same object? The forces they exert combine in different ways, depending on the directions in which they push.

Unbalanced forces in the same direction When two forces act in the same direction, the net force is the sum of the two individual forces. The object moves to the left. Predict which direction the object below will move.

Unbalanced forces in opposite directions When forces act in opposite directions, the net force is the difference between the two forces. The object moves to the right. Predict which direction the object below will move.

Balanced forces in opposite directions When two equal forces act in opposite directions, they cancel each other out. The object doesn’t move. Predict which direction the object below will move.