# Gravity and Satellites

In this worksheet, students look at what gravity is and how satellites are kept in orbit.

Key stage:  KS 4

Curriculum topic:  Physics: Forces

Curriculum subtopic:  Forces and Fields

Difficulty level:

### QUESTION 1 of 10

Gravity is the force of attraction between masses. It is the centripetal force needed to keep a satellite in orbit. The greater the mass of the satellite, the greater the force involved. A satellite can be a planet orbiting a star, like the Sun; an object orbiting a planet, like the Moon or a manmade satellite orbiting the Earth. Artificial satellites were launched in orbit around the Earth using a rocket. Satellites in lower orbits (nearer the Earth) travel faster.

Satellites in low polar orbits are used for forecasting the weather, spying and observing the Earth's surface. It takes them around 90 minutes to orbit the Earth. Geostationary satellites are in orbit above the equator. It takes them 24 hours to orbit the Earth and they appear to be in the same position. They are used for communications, such as mobile phones, satellite TV and GPS.

Orbits can be highly elliptical (oval), as opposed to circular. Periodic comets have highly elliptical orbits. When they are close to the Sun, the gravitational force is stronger than when they are further out. Their velocity changes as well, being higher close to the Sun and lower further from the Sun.

What is the force of attraction between masses?

friction

gravity

thrust

What type of force is needed to keep a satellite into orbit?

a strong force

a centrifugal force

a centripetal force

Name a natural satellite of the Earth.

the Moon

Saturn

Mars

Which of these is a satellite of the Sun?

periodic comets

the milky way

the Earth

What do we call satellites that are not natural?

artificial

unnatural

Which satellites are used for communication?

low polar orbits

geostationary

comets

How many minutes does it take low polar orbit satellites to orbit the Earth once?

20

90

900

19

Complete the following statement by selecting one of the options below:

Geostationary satellites appear to be....

over South America

over the North Pole

in the same position

Which space objects have highly elliptical orbits?

meteors

periodic comets

artificial satellites

When does the gravitational force act on periodic comets?

when they are close to the Sun

when they are far from the Sun

in the middle of their orbit

• Question 1

What is the force of attraction between masses?

gravity
EDDIE SAYS
Gravity is the force of attraction between masses. It is the centripetal force needed to keep a satellite in orbit.
• Question 2

What type of force is needed to keep a satellite into orbit?

a centripetal force
EDDIE SAYS
A centripetal force is a force that makes an object follow a curved path, and it is needed to keep a satellite into orbit.
• Question 3

Name a natural satellite of the Earth.

the Moon
EDDIE SAYS
The moon is the Earth's natural satellite.
• Question 4

Which of these is a satellite of the Sun?

the Earth
EDDIE SAYS
The Earth is a satellite of the Sun, as are all of the planets in our solar system.
• Question 5

What do we call satellites that are not natural?

artificial
EDDIE SAYS
Satellites that are not natural are called artificial.
• Question 6

Which satellites are used for communication?

geostationary
EDDIE SAYS
Geostationary satellites are used for communication, such as mobile phones, satellite TVs and GPS.
• Question 7

How many minutes does it take low polar orbit satellites to orbit the Earth once?

90
EDDIE SAYS
It takes low polar orbit satellites 90 minutes to orbit the Earth once.
• Question 8

Complete the following statement by selecting one of the options below:

Geostationary satellites appear to be....

in the same position
EDDIE SAYS
Geostationary satellites appear to be in the same position.
• Question 9

Which space objects have highly elliptical orbits?

periodic comets
EDDIE SAYS
Periodic comets have highly elliptical orbits.
• Question 10

When does the gravitational force act on periodic comets?

when they are close to the Sun
EDDIE SAYS
Periodic comets have highly elliptical orbits. When they are close to the Sun, the gravitational force is stronger than when they are further out. Their velocity changes as well, being higher close to the Sun and lower further from the Sun.
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