What is the best way to describe Newton's third law of motion?

Answer 1

A body experiencing a force F experiences an acceleration a related to F by F = ma, where m is the mass of the body. Alternatively, force is equal to the time derivative of momentum. (http://en.wikipedia.org/wiki/Newton's_laws_of_motion)

Basically, by exerting a force, the car propells itself and creates motion.

Answer 2

A toy car, sitting still, tends to remain still. When rolling, it tends to keep rolling. When rolling in a straight line, it tends to keep rolling in a straight line. Newton's 3 laws of motion.

Answer 3

Strictly speaking Newton's laws don't help the car move. The way things move was the same before Newton wrote his laws. Newton's laws do help to explain what is going on.

Newton's work formed the foundations for Physics (including his famous 3 laws) which led to engineering which led to the auto industry. You could argue cars wouldn't exist and therefore wouldn't move without Newton's laws.

Assuming this is a physics rather than philosophy question I'll try to answer the similar question "How do Newton's laws help to explain how a car moves?"

First Law "Every body remains in a state of constant velocity unless acted upon by an external unbalanced force."

A car is sitting on a flat road in neutral. It doesn't move. It's velocity stays the same, i.e. Zero.

A car is moving along a flat road at 50mph. You put it into neutral, it will continue to move at 50mph. It will slow down gradually due to friction (air and wheels)

2nd Law "A body of mass m subject to a net force F undergoes an acceleration a that has the same direction as the force and a magnitude that is directly proportional to the force and inversely proportional to the mass, i.e., F = ma"

A car of 600kg with a 100bhp engine will have a much shorter 0-60 time than a 1800kg car with a similar 100bhp engine.

A 1800kg car will need bigger brakes that can exert more stopping force than a 600kg car or it will take longer to stop.

3rd Law "The mutual forces of action and reaction between two bodies are equal, opposite and collinear."

When the petrol/air mix in an engine cylinder is ignited it forces the piston down but it also forces the cylinder head up.

Combining 2nd and 3rd laws

If a 1,000kg car travelling at 50mph drives head on into a 10,000kg lorry travelling in the opposite direction at 50mph the same force will apply to both vehicles but the car will accelerate much faster than the lorry. It will end up going backwards. If neither driver is wearing a seat belt the lorry driver probably won't be thrown through the windshield.

There are many more examples.

Answer 4

Newtons third law states that for every action there is an equal and opposite reaction.This means that as a force is exerted against an object an equal and opposite force of the same type with also be acting on the object.

For example, when you are stood up your weight acts down on the floor and at the same time the floor is exerting an equal and opposite contact force on your body.

Answer 5

Inertia of the test dummies as the car hits a barrier 'they' try to keep moving in a straight line. The seat belts and air bags have to 'save' the dummies. Analysis of 'damage' to the dummies helps determine how safe the car is.