How Is a Contact Force Involved in Pushing a Toy Car?
One of the basic laws of motion is that objects do not move unless some force is exerted upon them. When a force directly hits an object and causes it to move, that force is called a contact force. One of the primary examples of a contact force is that of a child pushing a toy car. To understand exactly what happens when a child pushes a toy car, you need to understand the variety of forces that influence the car's motion.
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Newton's Three Laws of Motion
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Newton's Three Laws of Motion explain how forces and objects interact. Understanding these laws is the foundation of understanding all motion, from a child pushing a toy car to a pilot flying an airplane.
The first Law of Motion is often called the Law of Inertia. It states that an object at rest will continue to stay at rest unless a force is exerted upon it. For example, a toy car that is sitting still will not move unless a force is applied to it.
The second law of motion states that a force is always equal to an object's mass multiplied by its acceleration. A corollary to this law is that the greater the force, the more quickly the object accelerates. In other words, the car won't move as fast if the child taps it as it will if he pushes it harder.
The third law of motion is that every action has an equal and opposite reaction. When the child pushes the car, an equal force pushes the child back in the other direction. The child's hand will move forward, but her body will fall back.
Types of forces
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Contact forces are forces that act directly on an object by coming into contact with it, such as the child pushing the car or friction between the wheels and the ground when the car is in motion. Non-contact forces have an effect upon the object but do not touch the object. Gravity is an example of a non-contact force.
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The car at rest
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Before the child pushes the car, the car is sitting in one place, not moving. This is called being "at rest." Gravity is pulling the car down towards the Earth, which is why it is on the floor and not floating up towards the ceiling. However, this is a non-contact force so it does not cause the car to move forward.
The moment of impact
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When the child pushes the car, her hand acts as a contact force. The force her hand exerts upon the car causes it to move forward. How fast the car accelerates depends upon how hard the child pushes it. The child's body will be pushed back by a force equal to the amount of pressure her hand exerts upon the car.
After the push
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After the child pushes the car, he no longer exerts a force over the car. However, as the tires move forward against the floor, the floor pushes equally against the tires. This force, which is called friction, eventually causes the tires to stop moving.
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References
- Photo Credit toy image by DXfoto.com from Fotolia.com
