Download 120409_Gravity LP

Miss Lee: 8th Grade Science (12/7/09)
Gravity & Inertia
AIMS / OBJECTIVES
SWBAT define gravity and explain how gravity influences the motions of celestial objects.
WHERE ARE WE GOING?
- Current Unit: Astronomy (Unit 6)
- Unit Exam will occur at completion of unit in 2 weeks
CATALYST
1. List the planets in order from closest to the sun to farthest from the sun.
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
2. Which planet do you think has the greatest gravitational pull to the sun? Which one do you think
has the least?
Mercury has the greatest because it is closest.
Neptune has the least because it is the furthest away.
MINI-LESSON/MODELING
Explain Ice Skating Tickets!
Show: http://www.amnh.org/rose/spaceshow/journey/
Show: http://videos.howstuffworks.com/hsw/12760-spin-around-the-solarsystem-gravity-and-inertia-video.htm
(See Below)
ACTIVITY
1. The two factors that combine to keep Earth and the moon in their orbits are
d. gravity and inertia
2. The tendency of a moving object to continue moving in a straight line or a
stationary object to remain in place is called c. inertia
3. All objects are attracted to each other by the force of
c. gravity
4. Explain how inertia and gravity combine to keep Earth in its orbit.
Inertia keeps an object moving in a straight line, while gravity pulls the
Earth towards the Sun. Combined, they pull the Earth in a circular orbit
around the Sun.
5. Identify one factor that keeps Earth in orbit around the Sun and the moon in
orbit around the Earth, both shown at right. Gravity or Inertia
MATERIALS
Poster, markers
6. Which of the three satellites at right (A, B, or C)
would experience the greatest pull of gravity
from Earth. Why? Satellite A because it is
closest to Earth.
7. What holds the planets in orbit around the Sun?
d. gravity
8. What four planets would experience the greatest pull of gravity from the Sun?
Why? Mercury, Venus, Earth, Mars (they are closest to the sun)
Too easy? Try some tenth grade questions. (Look up at the board for hints!)
***Have definitions on the board
9. Does a comet have a greater pull of gravity when it is aphelion or perihelion?
Why? Perihelion – because we are closer to the Sun
10. Planet A has a greater mean (average) distance from the Sun than planet B. On
the basis of this information, which other comparison must be true?
b. Planet A’s revolution is longer
Base your answers to questions 11 and 12 on the diagram below. The diagram
shows the relative strengths of the gravitational force for planets of different
masses. The size of each planet represents the planet’s relative mass. The arrow
length indicates the relative amount of gravitational pull that each planet would
exert on an astronaut in space.
11. What is the relationship between the mass of the planets and the relative
strength of their gravitational pull? The greater the mass of the planet, the
greater it’s gravitational pull. ***(Explain: F α mass of 2 objects)
12. Which three planets shown have less gravitational pull than Earth? Mercury,
Mars, and Pluto
HOMEWORK
- Write 8 sentences about what you learned (using the words: gravity, inertia, mass, force, etc.)
NYS Standard Ps1.1d
Gravity is the force
that keeps planets in
orbit around the Sun
& the Moon in orbit
around the Earth.
Definition
Force of attraction between two bodies,
proportionate to their two masses and
inversely proportionate to the distance
between them
Definition
Resistance of an object to a change in its
motion (an object in motion remains in
motion unless a force acts upon it)
G
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So What?
Sun pulls the Earth towards it
So What?
The Earth pulls forward in a straight line