Gravity and the solar system

LO: To define gravity and explain how satellites stay in orbit

1. The sun is the centre of what system? _____________

2. Name the largest member of our Solar System. ____________

3. Our solar system is in what Galaxy? ____________

4. What is the main difference between a planet and a star?

What is a satellite?

5. The Earth spins on its _____________.

6. The Earth revolves or travels around the ___________.

7. It takes the Earth _______ hours to spin on e complete time around

8. Explain why we have day and night.

9. Can you name the order of the planets closest to the sun outward?

• In pairs, discuss what these words meanforce gravitymassweight

Force

• a push or a pull

Gravity

• an attractive force between objects with mass

Weight• the force of gravity acting on a body (measured in Newtons)

Mass• the amount of material (atoms) in an object (measured in grams, kilograms etc.)

GravityGravity depends on 2 things:

If you double the distance the

gravitational force divides by 4…

F

F/4

1) The mass of the objects

2) The distance between them

F 2F

If you double the mass of one object

you double the force

9J Let’s stay togetherWhy do planets orbit the Sun? It’s the result of gravity.What will happen if you switch the gravity off?

Satellites• Satellites orbit planets- moon and artificial

satellites• To stay in orbit 2 forces must be balanced

Unbalanced forces = Too fast, fly off

Too slow, Pulled towards the object

Satellites

N

S

N

S

N

S

Polar

Low Earth

Geo stationary- orbits at same speed as the Earth

Space Junk

1. Draw the earth with a person on north and south poles2. Why does the person on the south pole not fall of the Earth?3. Which direction does the force of gravity pull you? Show this on the diagram.

4.What happens to the gravitational force between two masses if they move further apart?

5. What is weight?

6. What is the difference between weight and mass?

7. Does the force of gravity always stay the same? If not why not?

8. What happens to your weight on the moon?

9. What 2 forces allow satellites to stay in orbit?

10. If a satellite is in a low orbit, it will experience a greater force of gravity compared to a satellite in an higher orbit. What must happen to the centrifugal force (speed) for this satellite to stay in orbit?

launch pad on Earth

low Earth orbit

in space between Earth and Moon

on surface of Moon

Distances not to scale

9J The NASA diet?

An astronaut’s weight changes on a journey to the Moon.TASK: Match these weights to the astronaut’s position.

0 N 730 N 750 N 125 N

What happens at C?

750 N

730 N

0 N

125 N

Why is C nearer the Moon than the Earth?

Plenary

Task 1•What happens to the gravitational force between two masses if they move further apart?

•What is weight?

•What is the difference between weight and mass?

•Does the force of gravity always stay the same? If not why not?

•What happens to your weight on the moon?

Bonus Questions:

•What happens to your weight in space?

•Why do you think this happens?

Armageddon• a. What is gravity?• b. Why is there less gravity on the asteroid

than on the earth?• c. How does the reduced gravity help the

vehicle jump the ravine?

http://www.flickclip.com/flicks/armageddon5.html

Apollo 13• http://www.flickclip.com/flicks/apollo1302.htm

• a. What are the properties of the gravitational force? • b. How does the strength of the gravitational force compare

to the other forces in nature (i.e., electromagnetic, strong, and weak)?

• c. Does the gravitational force depend on mass? Distance? • d. Why are astronauts weightless in orbit about the earth?

Are they massless? • e. Explain why astronauts are able to carry heavy loads in

space that they would not otherwise be able to carry on earth.

• f. When astronauts make repairs (involving torque) on equipment in space, it is quite difficult. Explain why