Question

According to Newton's third law, when you push on an object, the object pushes back on you with an oppositely directed force of equal magnitude. If the object is a massive crate resting on the floor, it will probably not move. Some people think that the reason the crate does not move is that the two oppositely directed forces cancel. Explain why this logic is faulty and why the crate does not move.

A) The forces are not balanced
B) Friction opposes the motion
C) Gravity is acting downward
D) Inertia of the crate

Answer 1

The reason a massive crate does not move when pushed is not due to action and reaction forces cancelling out, as they act on different objects, but rather because friction and the inertia of the crate prevent its movement until the applied force is sufficient to overcome both.

Step-by-step explanation:

The logic that the crate does not move because the oppositely directed forces cancel each other is faulty because the forces of action and reaction act on different objects and therefore do not cancel each other out. When you push on a crate, the force you exert on it is matched by an equal and opposite force the crate exerts on you, as per Newton's third law of motion. The crate does not move because the friction between the crate and the floor is greater than or equal to the pushing force, causing no net movement on the crate. Additionally, the inertia of the crate, which is its resistance to change in motion, also contributes to its lack of movement until the force applied overcomes both friction and inertia.