Satellites and orbits

Question 1

bodies of lower and higher mass

Answer 1

bodies of lower mass travel in orbits around bodies of much higher mass

Question 2

natural satellites

Answer 2

formed by natural processes

e. g.
- eight planets which orbit the Sun
- moons
- comets

Question 3

artificial satellites

Answer 3

manufactured and launched into space from Earth using rockets

Question 4

geostationary orbit (3)

Answer 4

satellite orbits the planet at the same rate/speed as the planet (takes 24 hours to orbit the Earth)

it stays in one place above Earth in orbit

much higher than polar orbits, so the satellites travel slower (~3km/s)

Question 5

polar orbits (3)

Answer 5

take the satellite over the Earth’s poles

travel very close to the Earth (as low as 200km) so they travel at very high speeds

eventually travels over all points on the Earth

Question 6

low Earth orbits (2)

Answer 6

need the least fuel for launching satellites

move at 7,500 m/s

Question 7

elliptical orbits

Answer 7

are further out from Earth

oval shaped

Question 8

uses for geostationary orbits (2)

Answer 8

broadcasting

global positioning satellite systems (GPS)

Question 9

uses for polar orbits (4)

Answer 9

weather monitoring
military
spying
Earth observation purposes

Question 10

other uses for satellites

Answer 10

orbiting and monitoring the Sun, other planets, or asteroids

Question 11

Why are some orbits not steady? (3)

Answer 11

• if the satellite moves too quickly the gravitational attraction between the Earth and the satellite will be too weak to keep it in orbit, and it will move off into space
• if it moves too slowly the gravitational attraction will be too strong, and the satellite will fall towards the Earth
• in a stable orbit the speed is just right, and it will not move off into space or spiral towards Earth, but travels on a fixed path

Question 12

Explain the relationship between speed, direction, velocity and acceleration of a satellite in orbit

Answer 12

the speed of a satellite in orbit is constant

when an object moves in a circle at a constant speed, its direction changes

a change in direction causes a change in velocity

this is because velocity is a vector quantity, it has direction and magnitude

a change in velocity results in acceleration, so an object moving in a circle is accelerating even with a constant speed

Question 13

satellites and centripetal force (4)

• resultant force
• orbits

Answer 13

an object only accelerates if a resultant force acts on it

centripetal force is the resultant force for an object moving in a circle

centripetal force acts towards the middle of the circle

gravitational attraction provides the centripetal force needed to keep planets and satellites in orbit

Question 14

orbits and changing speeds (6)

• lower/higher orbits
• resultant force
• stable orbits

Answer 14

gravitational attraction between two objects decreases with distance

satellites closer to the earth have a greater resultant force (gravity), a greater force causes a greater acceleration needed to stay in a stable orbit

a greater acceleration means a greater velocity, so lower satellites/small orbits must move faster to avoid falling down to earth

a satellite could also move higher instead of speeding up

objects in higher orbits can travel slower as there is less resultant force acting on them due to the greater distance, so less acceleration is needed

objects also can’t travel too fast, as they will fly off into space

Question 15

What does a satellite have to do to maintain a stable orbit when changing speed?

Answer 15

it must also change the radius of its orbit

if it changes the radius of its orbits it has to change its speed

Question 16

examples of elliptical and circular orbits

Answer 16

planets orbiting the Sun/artificial satellites of the Earth tend to move in near-circular orbits

the orbits of comets around the sun are highly elliptical

Question 17

why are some orbits elliptical?

Answer 17

• the gravitational force of the sun on the comet gets weaker as it moves further away
• the comet travels slower when it is further from the sun, and faster when it is closer
• the gravitational force on the comet is greater as it is closer to the sun, so it orbits it more closely

(comets are influenced by other bodies with a gravitational force in the solar system)

Question 18

Compare the motion of Earth, Jupiter and Saturn as they orbit the Sun [3]

Answer 18

• all three travel in circular orbits
• all three have a constant speed and a changing velocity, so are accelerating
• as the distance from the Sun increases, the orbital speed decreases
• the Earth has a higher orbital speed than Jupiter, which has a higher speed than Saturn

Question 19

State the nature of the speed and velocity of a body that is moving in a circular orbit [2]

Answer 19

speed of a body in circular orbit is constant, but velocity is changing as the direction of the body is constantly changing

Question 20

Explain how the speed and velocity of a comet changes over the course of one orbit [4]

Answer 20

speed is greatest nearest the Sun, velocity changes the most near the Sun as direction changes most when nearest the Sun

Question 21

Explain what might happen to a GPS satellite if its orbital speed changed [6]

Answer 21

orbital speed increases, radius of orbit decreases as centripetal force exceeds that of gravitational pull (to stop it flying into space)

orbital speed decreases, radius of orbit increases as gravitational pull greater than centripetal force (to stop it falling towards Earth)