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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?

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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 . –  anna v May 18 '13 at 9:01
Possible duplicates: and links therein. –  Qmechanic May 18 '13 at 10:47
It's all a lever really. The engine block pushes down on the piston (via pressure) which twists the crankcase (acting as a lever) with the payload side (via gearing) the mass of the car. –  ja72 Jan 2 at 21:32

4 Answers 4

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.

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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.

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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

If you pushed very hard on the dashboard and let your effort throw you into the back seat, you might be able to move the car a little. When you landed the car might move back the other way. Internal forces within a system can move parts of it. Newtons first law applies to the center of mass of a system.

"External force" on a system can be a reaction force to the system exerting force on something else. For example, if you opened the car door and used your foot to push the car forward you might be able to move the car. The force your foot is exerting on the ground is not an external force upon the system of you and the car. But the equal and opposite frictional force from the ground on your hand or foot is an external force to the system.

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the engine produces energy that is transferd to the gear box. from there the gear box spins the axel and moves the tire that moves the car

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