What is motion?

An object is in motion if it changes position over time compared to a

reference point.

What is a reference point?

• An object or background that appears to stay in place in relation to (compared to) a moving object.

What do we assume about a reference point?

• We assume a reference point is not moving or stationary.

Most common reference point?

The most common reference point is the Earth or the Earth’s surface.

Name typical reference directions

• North, South, East, West, up or down, left or right, etc.

Can a moving object be used as a reference point? Explain using the bird

and balloon example.

• Yes• A bird flies by a hot-air balloon. The moving

balloon is compared to the moving bird. The bird changes position relative (compared) to the balloon.

Do the Quick Lab on page 337. Answer questions 3,4, and 6.

• The new position is -3 from the reference point.

• (answers will vary)

• + and – signs are needed to know whether to move your finger right or left.

You pass by a white car. If the car you are in (the red car) is your reference point, the white car appears to be moving backward. In other words, if you compare the white car to your car, the white car is moving backwards. If you compare the white car to the surface of the Earth it is moving forward. In other words, if the Earth is the reference point the white car is moving forwards. In conclusion, the direction an object is moving depends on the reference point (what you are comparing it to).