1. Solar System
Focus Question: How do the planets
stay in orbit?
Inv 1-2

2. A Tour of the Solar System
Response Questions
 What is the Sun, what is it made of?
 What is the solar system?
 What planets are terrestrial planets?
Gas Giants?

3. Response Questions, cont.
 What is the Kuiper Belt, what is found
there?
 Which planet has the most moons?
 How are asteroids and comets alike,
different?

4. Orbit
 Sir Isaac Newton
– Studied moving objects
– Three Laws of Motion
 Newton’s first law of motion
– Moving objects travel at a constant speed in a
straight line.
– A moving object can change speed and/or
direction only when a force pushes or pulls it.
 How can planets orbit the Sun if objects only
move in straight lines?

5. Orbit Demonstration
 Ball - String
– What made the planet travel in a circle?
– Newton’s law says objects travel in straight lines
unless acted on by a force
 Planets are moving objects
– Move in circular orbits around the Sun
– Must be a force pulling on planet that changes its
direction constantly
 Gravity
– Sun’s gravity is pulling on the planets
– Gravitational attraction between Sun and planets
keeps planets moving in circular orbits

6. Why Doesn’t Earth Fly Off
Into Space?
 Why do planets stay in orbit around the
Sun?
 How is a ball on a string like a planet in
its orbit?
 What keeps the Moon in its orbit
around Earth?
 Homework – Read Ramon E. Lopez,
pg 159 and Mae Jemison: Astronaut,
page 162-3

7. Planets and the Solar System
Video Notes
 Why is the system of sun and planets
called the solar system?
 Which planets are inner planets?
 Which planets are outer planets?
 How are the inner and outer planets
different?
 Which planet is closest to the Sun?
Why isn’t it the hottest planet?

8. Video Notes – con’t.
 What is meant by the rotation and
revolution of a planet?
 What other planets, beside Earth,
might support life?

9. Vocabulary
 Gravity
– The force of attraction between two objects;
larger bodies, like the Sun, have a greater force
of gravity.
 Inertia
– Moving objects stay in motion, in a straight line,
unless something acts upon them
 Revolve
– To travel in a path or orbit around another object;
for example, Earth revolves around the Sun.

10. Vocabulary
 Revolution
– Occurs when an object travels in an orbit
and returns to its starting position. It takes
Earth one year to make a complete
revolution around the Sun.
 Rotate
– To spin or turn around on an axis or center
point. Earth makes one complete rotation
every 24 hours.

11. Content
 What is gravity?
– Gravity is the force of attraction between two
objects.
– Larger objects, like the Sun, have a greater force
of gravity
 Why do planets travel around the Sun in
circular paths?
– Gravity pulls on planets with a force that changes
their direction of travel from a straight line into a
circle
 Your questions?

12. Summary: Solar System
 What are the main objects in the solar
system? How are they alike or
different?
 What is the Sun? What is it made of?
What is its role in the solar system?
 Why do the planets and other objects
in the solar system stay in their orbits?
 Quiz on Wednesday, May 6th