# Forces That Are Used In a Car

• Though forces affect us constantly, they are most noticeable when we are moving at high speeds, such as in a car. The four main types of forces that influence a moving car are thrust, drag, weight and cornering.

## Thrust

• Thrust is the force that causes a car to move forward. In vehicles, thrust is created when the power of the engine is harnessed through the turning wheels. In physics, every object has an equal and opposite reaction. This means that when the turning wheels push against the surface of the road, the car is moved with force in the opposite direction.
Thrust cannot be generated if the wheels are unable to push against the road. This is why a vehicle on ice does not move quickly. The more force the wheels are able to exert against the surface, the faster the car will move down the road.

## Drag

• The force affecting a car in the opposite direction than it is moving is called drag. Drag is caused by the resistance of air pushing against the large surfaces of a vehicle. These forces slow the vehicle, requiring more thrust to maintain speed. Drag caused by air resistance is the reason that many cars have streamlined designs.
Any time that the force of thrust is greater than the force of drag, the car will accelerate forward. If thrust drops, such as when the engine slows down, drag becomes the greater force and the vehicle decelerates. If thrust and drag are kept equal, the speed of the car remains constant.

## Weight

• Weight is the force of gravity pushing a car toward the ground. This force is essential to vehicles. Without this force, wheels could not stay in contact with the road and no thrust could be generated. Besides keeping the wheels on the ground, weight can affect vehicles in several other ways. When a car is driving up a hill, gravity constantly pulls it backward. To offset the force of this weight pulling against the car on a hill, increased thrust is needed. This is why an engine must work harder to move a car up a hill, compared to a flat surface.
Weight and gravity can sometimes have dangerous effects on cars. When cornering, vehicles can tilt. If the vehicle is tall enough, the force of gravity pulling against its body can pull it completely off of the road. A rollover occurs when the force of weight is no longer planted on the wheels.

## Cornering

• Cornering forces, also called lateral forces, affect a car when it is turning. It is a law of physics that an object in motion tends to stay in motion, continuing on its original path. This is known as inertia.
The cornering force of inertia is most noticeable during tight runs and curves. As a car turns, its mass, including the passengers, have an inertia that tends to stay moving in a straight line. This causes them to be pulled in the opposite direction of the turn.