In Newton's own words Moving and stopping

Newton was the first to understand that friction and air resistance were actually forces acting to slow the motion of a moving body.

"If a body is at rest it will remain at rest. If it is in motion it will remain in motion at a constant speed in a straight line, unless it is acted upon by a force." This law is a consequence of the concept of inertia and is the reason we should wear seat belts!

This was quite a change in thinking at the time, because up until then people had followed Aristotle's thinking that a force was required to keep an object in motion. This is the result of simple observation of objects in motion on Earth, where air resistance and friction are often acting on the body.

In Newton's own words
(To be read only for historical insight. The mixture of old English and terminology can confuse!)

Every body preserves its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by force impressed thereon.

Projectiles preserve their motions, so far as they are not retarded by the resistance of the air, or impelled downwards by the force of gravity. The greater bodies of the planets and comets, meeting with less resistance in more free spaces, preserve their motions both progressively and circular for much longer time. "Principia - 1726"

Projection and air resistance

Moving and stopping
When a car quickly moves away from traffic lights the passengers are thrown backwards into their seats. If the car brakes suddenly they are thrown forward. The passengers' movement in a car is a direct consequence of Newton's 1^st law of Motion.

At the traffic lights the passengers' bodies were at rest. The car accelerated away from the lights as a force was applied by the engine through the tyres onto the road surface.

The car, being well and truly attached to the tyres, moved forward. The axle exerted a force on the car to achieve this motion. The passengers being not so well attached to the car, tended to stay at rest until they were pushed forward by their seats.

Similarly on stopping, the passengers retained their forward motion and, relative to the car, seemed to be thrust forward.

Modern cars have seat belts and head rests to help make the passengers part of the car and move with the car as forces are applied.

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