Chapter 8 Lesson 3 In 1543, Copernicus published On the Revolution of the Heavenly Spheres, a book based on his 30-year study of the solar system.

Describing & Measuring Motion TODAY’S KEY QUESTION When is an object in motion?

A change in position relative to another object Motion A change in position relative to another object

The red car moved. The boy stayed in the same position relative to the flag pole. The flag pole, the school building, the trees,…

Reference Point A place or object used for comparison to determine if something is in motion An object is in motion if it changes position relative to a reference point

Relative Motion When you do not seem to be moving because the other thing is moving too! When you ride in a car & the sun or moon seem to follow you… Earth moves ~30km every second You and everything on Earth are moving quickly (as well as riding in the car) So you do not ‘seem’ to move

Because of Earth’s spin, the stars appear to move in circular arcs across the night sky. Only the North star remains in a fixed position. Historically, sailors have used the North Star to help them navigate

The people are NOT moving relative to each other. They ARE moving relative to objects on the ground. The objects on the ground stay in the same place. When I describe the motion of people, I should choose a reference point that doesn’t move.

International System of Units What is the system of measurement scientist use? Distance What is the length of the path between two points?

1000 100 6.5 cm 100 cm/6.5 cm = 15 spiders

Reference point It’s position changes relative to a reference point. If your reference point is moving, then you won’t know if you are moving or not.