GED Science › Newton's Third Law
Which of the following is the best example of Newton's Third Law?
If an object's weight rests on the floor, then the floor will exert a normal force on the object
A spinning top will not fall unless there is friction with the surface on which it spins
When two objects collide, the total initial and total final momentum will be equal
The force of being hit by an object is determined by its mass and acceleration
Newton's Third Law states that for every action there is an equal and opposite reaction. In other words, a force will act in equal and opposite directions on the two objects involved.
Weight and normal force are a specific example of this principle. Acceleration due to gravity creates a downward force, known as weight. This force, however, results in zero downward acceleration when the object is resting on a surface (a book does not fall through a table, for example). For the forces to be in equilibrium, there must be a counteracting upward force. This is known as the normal force, which is equal and opposite to the weight of the object. While weight pulls the object down, normal force pushes it up to create equilibrium.