Focus Question: How do the planets
stay in orbit?
A Tour of the Solar System
What is the Sun, what is it made of?
What is the solar system?
What planets are terrestrial planets?
Response Questions, cont.
What is the Kuiper Belt, what is found
Which planet has the most moons?
How are asteroids and comets alike,
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
– 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?
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
– Sun’s gravity is pulling on the planets
– Gravitational attraction between Sun and planets
keeps planets moving in circular orbits
Why Doesn’t Earth Fly Off
Why do planets stay in orbit around the
How is a ball on a string like a planet in
What keeps the Moon in its orbit
Homework – Read Ramon E. Lopez,
pg 159 and Mae Jemison: Astronaut,
Planets and the Solar System
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
Which planet is closest to the Sun?
Why isn’t it the hottest planet?
Video Notes – con’t.
What is meant by the rotation and
revolution of a planet?
What other planets, beside Earth,
might support life?
– The force of attraction between two objects;
larger bodies, like the Sun, have a greater force
– Moving objects stay in motion, in a straight line,
unless something acts upon them
– To travel in a path or orbit around another object;
for example, Earth revolves around the Sun.
– 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.
– To spin or turn around on an axis or center
point. Earth makes one complete rotation
every 24 hours.
What is gravity?
– Gravity is the force of attraction between two
– Larger objects, like the Sun, have a greater force
Why do planets travel around the Sun in
– Gravity pulls on planets with a force that changes
their direction of travel from a straight line into a
Summary: Solar System
What are the main objects in the solar
system? How are they alike or
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