Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

Newton's First Law of Motion states that an object at rest or uniform motion tends to stay in that state of motion unless an unbalanced, external force acts on it. Say if I were in a car and I push it from the inside. It won't move. So how is the engine of a car capable of moving the car?

share|improve this question
If you push the car from the bumper, will it move? How? The wheels will turn by the friction the tires find, instead of sliding as it would on ice. In a pedal pusher children's car the pedals turn the wheels.The energy supplied turns unto rotatonal energy and friction forces into linear momentum of the center of mass.hyperphysics.phy-astr.gsu.edu/hbase/mechanics/auto.html . –  anna v May 18 '13 at 9:01
Possible duplicates: physics.stackexchange.com/q/45653/2451 and links therein. –  Qmechanic May 18 '13 at 10:47

2 Answers 2

The car's engine tries to make the wheels turn. However, the wheels encounter friction against the road so they cannot just spin. As the road has much higher inertia than the car, it will not move when the wheels want to turn. Instead, it is the car that moves.

The end effect is that the engine pushes against the road, just as you do when you push the car: your feet are on the road, allowing you to push the car forward. In the case of the car, the wheels are on the road and they can push the car.

Pushing the car assumes you have enough force, and the road is not too slippery. This also applies to the engine: if it does not have enough power, or the road is too slippery (icy), it cannot push the car.

share|improve this answer

Each force causes reaction (3rd law). If move a car from the inside the car moves you as well. That's because you are pushing or pulling. However the engine does not push but converts energy in other directions, usually a rotating one (the same as riding a bicycle). This rotating force has its counter-force which is reaction of ground.

Pushing a car you use a friction force. Pushing from the inside this force is caused bythe object itself, not solid ground.

share|improve this answer
Ah that clears it. Thanks –  Abhi2011 May 18 '13 at 8:59
It's wheels what moves a car, not the engine –  Voitcus May 18 '13 at 9:34

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.