Newtons Laws and the Car

Newton’s First Law – The law of inertia

Newton’s first law states that that moving objects tend to keep moving at the same speed and in the same direction or objects at rest will stay at rest unless and unbalanced force acts on it.

One aspect of a car that relates to Newton’s first law is how if a car a car will continue doing what its doing unless an unbalanced force is applied. For example a car parked in a driveway will not drive forward or reverse unless an unbalanced force is applied. When in motion a car travelling at 50m/s will continue travelling at 50m/s unless acted upon by an unbalanced force.

Another aspect of the car that relates to Newton’s first law is the head rests in the car. When you’re in a rear end collision the head rests help to prevent whiplash. Head rests help because when the car behind bumps into the rear of your car it creates an unbalanced force pushing the car forward but because there isn’t an unbalanced force pushing you forward as well, your body stays in the same position causing your body to push against the car seat. With out the head rest your head wouldn’t be supported and could cause serious neck injuries.

Seat belts are another example of Newton’s first law. If you are wearing a seatbelt when a car slows down, the seatbelt acts as an unbalanced force on you and therefore changes your state of motion so you’re the same as the cars. For example if a car is moving at 40km an hour, hits a brick wall and stops, you will still be going at 40km an hour. If a seatbelt isn’t being worn it you would be most probably be launched from the car and thrown through the air. This is because no unbalanced force has acted on you, just the car, so there was nothing to change your state of motion.
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Newton’s second law

Newton’s second law states that when an unbalanced force acts on an object it produces an acceleration in the direction of the force. The acceleration is directly proportional to the size of the force and is inversely proportional to the mass.

One aspect of a car is its engine. The force from the car engine provides an unbalanced force causing the car to accelerate, the bigger the engine is the greater amount of force can be applied to the car and therefore allowing the car to accelerate faster.

Because force is inversely proportional to mass, meaning the smaller the mass the higher the acceleration. The lighter the car the faster and easier the car can accelerate whereas the heavier the car the slower and harder it is for the car to accelerate.

An example would be if a truck bumped into a car. If the car was very light it would move forward quickly (higher acceleration) than it would if the car was heavier.

Newton’s third Law (Action – reaction)

Newton’s third law states that for every force there is an equal and opposite force. A car at rest will have 2 forces acting on it. Its weight pulls the car to the ground while the ground pushes back on the car with an opposite and equal force.

Another aspect is that on the car the wheels are designed to spin backwards, while they spin backwards they grip the road and push the road backwards. Mean while because of Newton’s third law, this force makes the road push the car wheels forward. The size of the force on the road is the same size as the force on the wheels and the direction of the two forces on the road and the wheel are opposite.

Every action there is an equal and opposite reaction. The person is pushing the car with a force of 100 N and a force of 100 N is going in the opposite direction so the car doesn’t move.

This law also shows how a car’s crumple zones work. When you crash into another car, your car hits the other car but also sends another force back onto your car. The crumple zones on the car are made soft so they absorb energy on impact, which helps to make the time that your car takes to stop completely spread out over a longer period of time. This means that your car slows down over a longer period of time, so the force acts over a longer time and the shock to your body is less.