This is part of a series on common misconceptions.
True or False?
I exert a force on a car, and the car also exerts an equal and opposite force on me by Newton's third law. Hence I should not be able to move the car ever.
Why some people say it's true: That's Newton's third law!
Why some people say it's false: Because I can push a car and get it to move.
The statement is .
Explanation: First, figure out the action-reaction pair. Applying a force on the car is the action and the friction from the ground is the reaction and not the reaction from the car, because action-reaction pair deal with two different bodies. The forces do not cancel out. We should only be summing up forces on a particular body. So, the car experiences a force from me, and if that force overcomes friction, the car will move! Further, the action and reaction forces need not act on the same body.
Further Explanation: Newton's third law tells us that we have conservation of momentum in a system, because the forces are equal and opposite. Since force is the rate of change of momentum, the cancellation of force means that there is no change in momentum (of the system). However, this doesn't yet give us information about a part of the system during the interaction of forces.
Rebuttal: Every action has an equal and opposite reaction, so when I push the car, it should not move because of friction.
Reply: But, if the action (that is, the force applied by us) exceeds the magnitude of limiting friction, then the car would move because, at this point in time, the force applied by us is sufficient enough to overcome the friction.
See Also:
- List of Common Misconceptions
- Newton's Third Law
- Conservation of Momentum
