1. 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.

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

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

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

5. 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

6. 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

7. 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

8. 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.

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

10. 1000
100
6.5 cm
100 cm/6.5 cm = 15 spiders

11. 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.