Newton’s law of motion explains how Jerod starts his skateboard moving. This law states that every has an . This means that forces always act in . First an occurs—Jerod pushes against the ground with his foot. Then a occurs—Jerod moves forward on his skateboard. The reaction is always in to the action but in the direction.

Equal and Opposite Forces
The forces involved in actions and reactions can be represented with . The way an arrow points shows the of the force, and the size of the arrow represents the of the force. Look at the skateboarders in the Figure below. In the top row, the arrows represent the with which the skateboarders push against each other. This is the . In the bottom row, the arrows represent the forces with which the skateboarders move . This is the . Compare the top and bottom arrows. They point in different , but they are the same . This shows that the forces are and to the forces.