A force can do one of four things to an object:

Example 2:

1. An object is dropped from a height of 120 feet.
2. If h is measured in feet, t is the number of seconds the object had fallen, and h0 is the initial height from which the object was dropped, then the model for the height of falling object is:
3. h=−16t2+h0.
4. Substitute 0 for h and 120 for h0 in the model.

Newton’s third law of motion is naturally applied to collisions between two objects. In a collision between two objects, both objects experience forces that are equal in magnitude and opposite in direction. Such forces often cause one object to speed up (gain momentum) and the other object to slow down (lose momentum).

• Make it speed up – accelerate.
• Make it slow down – decelerate.
• Change its direction.
• Change its shape.

When a force pushes or pulls the object, the object will move in the direction of the force. The bigger the force, and the lighter the object, the greater the acceleration. It can also make something slow down, speed up or change direction.

Draw conclusion: What causes objects to slow down when they are no longer pushed? The reason why the objects started to slow down when they were no longer pushed was because there was friction acting on the wheels, causing the object to slow down and eventuallystop.

In order for there to be continuous motion, there must always be a force acting on it. Why some people say it’s true: Any object which moves eventually comes to stop. Thus, to keep it in motion, a force must be applied.

The force that brings nearly everything to a stop is friction,which is the force that acts to resist sliding between two touch- ing surfaces, as shown in Figure 3. Friction is why you never see objects moving with constant velocity unless a net force is applied.

friction