Motion is an event that involves a change in the position or location of an object.

Motion is described in terms of speed, velocity, and acceleration. Let's review these terms.

• Speed tells us the rate at which an object moves. Speed is a comparison of time and distance.
• Velocity tells us the speed and direction of a moving object.
• Acceleration is a change in velocity. Acceleration can be caused by a change in either speed or direction.

Describing the motion of an object is hard to do with words. Sometimes graphs help make motion easier to picture and, therefore, to understand. A graph is a pictorial representation of data. There are two types of motion graphs:

• Position (distance) vs. time graphs
• Velocity vs. time graphs

Motion graphs can tell a story. Analyze the graph below. Select the description that you think best matches the data shown in the graph. Write your answer choice and two reasons to support your decision.

1. Robert took his dog for a walk to the park. He started out slowly and then increased his pace. At the park, Robert turned back around and walked slowly back home.
2. Robert rode his bike east from his home up a steep hill. After a while, the slope of the hill eased off. At the top of the hill, he raced down the other side.
3. Robert went for a jog. At the end of his road, he bumped into a friend and his pace slowed. When Robert left his friend, he walked quickly back home.

Save your answer choice and your reasons. We will return to this graph again later in the lesson.