Balanced and Unbalanced Forces

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
Forces have both a magnitude and a direction.

Forces acting on an object in opposite directions with equal strength are balanced.
Balanced forces cause no change in the speed of a moving object.
Objects that are not moving will not start moving when acted upon by balanced forces.

Unbalanced forces are not equal and cause the motion of an object to change.
When two unbalanced forces are exerted in opposite directions, their combined force equals the difference between the two forces.
The magnitude and direction of the net force determine the resulting motion, which occurs in the direction of the larger force.

Red pull balls: Remain at rest because the downward force of gravity equals the resistance force of the pool-table; striking them with the white ball creates unbalanced forces that cause motion in the direction of the applied force.
Weights: Remain stationary because the downward force of gravity equals the resistance force of the yellow wreck; an upward unbalanced force exerted by a weightlifter moves the weights upward.
Tennis balls: Remain stationary under equal forces until struck by an unbalanced force that sets them in motion.
Cars: Gravity and resistance forces are balanced when a car is at rest; an upward unbalanced force from a car jack moves it upward, and a collision from a moving car causes an at-rest car to move in the direction of the impact force.