MODULE mod7A mod7B mod7C mod7D mod7E mod7F mod7G mod7H mod7I mod7J mod7K mod7L mod8A mod8B mod8C mod8D mod8E mod8F mod8G mod8H mod8I mod8J mod8K mod8L mod9A mod9B mod9C mod9D mod9E mod9F mod9G mod9H mod9I mod9J mod9K mod9L 9ja1
9Ja1 Gravity questions
Name _____________________________ Class ____________
1 On the Earth, gravity pulls with a force of 10 N on every kilogram of mass.
To find the weight of a particular mass, multiply the mass by 10. If you know the weight and want to find the mass, divide by 10.
Fill in the gaps in this table.
Object
Mass (kg)
Weight (N)
television
8.0
radio
1.5
chair
50
bag of sugar
1.0
bottle of lemonade
20
2 If we are measuring small masses, we usually use grams instead of kilograms. If we have a mass in grams, we need to convert it to kilograms before we find the weight. To change a mass in grams into kilograms, divide by 1000.
Fill in the gaps in this table. The first one is done for you.
Mass (g)
jar of jam
340
0.34
3.4
bag of pasta
500
tin of beans
450
loaf of bread
800
can of lemonade
330
3 Why don't people in Australia feel like they are upside down?
__________________________________
_________________________________
4 The person on the top of the Earth is holding out a sports bag.
Draw in a sports bag for the other person.
[ knowledge, numeracy ]
9Ja2 Lifting the load
When a spacecraft like the Space Shuttle is launched, the upwards force from the engines has to be bigger than the weight of the shuttle.
If the shuttle is very heavy it will need large engines to produce the force required, and the engines will use a lot of fuel. The engines and the fuel all cost money, so engineers need to keep the engines as small as they can. They are able to do this by keeping the mass as small as possible.
One way of keeping the mass down is to throw away parts of the launch vehicle as soon as they have been used. The Space Shuttle needs a lot of
fuel to get into orbit. The solid rocket boosters burn for about two minutes before all their fuel is used up. The boosters are then separated, and parachute back down to Earth. They can be recovered and used again.
The orbiter's main engines are also used during take-off. They use oxygen and hydrogen from the external tank. When all the fuel is used the tank is separated from the shuttle. This happens about nine minutes into the flight. The shuttle is about 100km high at this point, and the tank burns up as it falls back into the atmosphere.
If the boosters and the external tank stayed on the orbiter it would be more difficult to get it into orbit because it would be heavier. At the end of the mission the orbiter re-enters the atmosphere and glides back to its base. It has no fuel left, so the pilot has to land it properly on his or her first attempt.
1 Why do engineers need to keep the mass of spacecraft as low as possible?
2 How is the mass of launch vehicles kept as low as possible during a space flight?
3 What fuel do the Space Shuttle's main engines use?
4 Which part of the Space Shuttle does not get reused?
5 How and why will the mass of the whole space vehicle change:
a during the first 2 minutes of the flight?
b when the boosters are separated?
c between the 2nd and 9th minutes of the flight?
d while the Space Shuttle is in orbit?
6 The rocket used to send astronauts to the Moon was called a Saturn V (Saturn five) rocket. No parts of the Saturn V were reused. Find out what a Saturn V looked like, how many engines it had, and which parts were jettisoned during the space flight.
[ literacy, knowledge, research ]
9Ja3 Changing gravity
When we calculate the weight of a particular mass, we assume that Earth's gravity pulls on every kilogram of mass with a force of 10 N. This is only an approximate value. If you needed more accurate results, you should use the number 9.81 N/kg.
But even this number is not completely accurate. The strength of gravity is different at different places on the Earth. One reason for this is that the Earth is not actually spherical. The radius of the Earth at the Equator is about 21.5 km more than the radius at the poles. The Earth is a slightly squashed sphere.
The gravitational attraction between two objects depends on how far apart they are, as well as on their masses. This means that the strength of gravity at the poles is about 9.832 N/kg, and at the Equator it is about 9.780 N/kg.
This is not the complete story! The Earth's crust is not made of the same rocks everywhere. If there is a particularly dense area of rock under the surface, gravity will be a little stronger on the surface of the Earth above it. Geologists can find out something about the structure of the Earth's crust by making very sensitive measurements of the strength of gravity at different places. This is a complicated procedure, because they also have to take into account the effect of any nearby mountains or hills. The differences in the strength of gravity between different places are so small that scientists use a different unit, the gal. 1 gal is equivalent to a difference in the strength of gravity of 0.01 N/kg.
1 a Why is the strength of gravity different at the poles and the equator?
b Explain why gravity is stronger at the poles.
2 a What is the difference in gravity between the Equator and the poles?
b What is the difference in gals?
3 Why do you think that we generally use a mean value of 9.81 N/kg when calculating weight?
4 Scientists often use milligals (mGal) as units when doing gravity surveys.
a Why do you think they need to use milligals?
b What gravity difference do you think a milligal represents? (Hint: Think about the difference between a metre and a millimetre.)
5 a Why will a dense area of rock under the surface increase the local strength of gravity? Use the word 'mass' in your answer.
b Sometimes rocks can be less dense than the surrounding crust. What effect do you think a less dense area of rock would have on the strength of gravity? Explain your answer.
6 The unit for gravitational differences was named after Galileo. Find out why the unit was named after him.
[ literacy, numeracy, research ]
9Jb1 Going to the Moon
In 1969, the first people landed on the Moon. The pictures below show different stages in their journey.
1 Cut out the pictures and arrange them in the correct order. Stick them into your book.
2 Write a sentence for each picture, explaining how gravity is affecting
the spacecraft.
3 The boxes at the bottom of the page show the mass and weight of an astronaut at different stages of the journey. Cut out these boxes and match them with the correct stage in the journey. Stick them into your book.
4 Write a couple of sentences for each picture. Explain why you have matched the weight with the picture, and describe how it might feel to be an astronaut in the spacecraft.
[ knowledge ]
---------------------------------------------------------------------------------------------------------
The spacecraft is lifting off from the Earth.
The lunar module joined up with the rest of the spacecraft that was orbiting around the Moon. The astronauts got back into the main part of the spacecraft.
Most of the rocket was dropped before the spacecraft got into Earth orbit. These parts of the spacecraft went to the Moon.
This is the only part of the spacecraft that returned to Earth.
The lunar module landed on the Moon.
Only the top part of the lunar module took off again.
Only the command module came through the atmosphere.
These parts of the spacecraft stayed in orbit around the Moon.
mass = 80 kg, weight = 770 N
mass = 800 kg, weight = 800 N
mass = 80 kg, weight = 0 N
mass = 800 kg, weight = 133 N
mass = 80 kg, weight = 100 N
9Jb2 Gravity on other planets
Some planets have stronger gravity than others. Gravity depends on the size of the planet. On Earth, gravity pulls on every kilogram with a force of 10 newtons.
You can work out the weight of something if you know its mass and the strength of gravity. The strength of gravity is 10 N/kg on Earth, but only 1.6 N/kg on the Moon.
weight (N) = mass (kg) × strength of gravity (N/kg)
1 Work out the weights of these objects on the Earth and on the Moon.
Weight on Earth (N)
Weight on the Moon (N)
hammer
1
box of books
12
oxygen cylinder
box of food
8
2 Imagine that you had to move the things in question 1 around on the Moon.
a In what way would it be easier to move them on the Moon than on the Earth?
______________________________________________________________________
b In what way might it be more difficult?
3 Now work out what your weight would be on other planets if your mass is 40 kg. Write your answers in the table. Saturn has been done for you.
Planet
Gravity (N per kg)
Mercury
3
40
Venus
9
Earth
10
Mars
4
Jupiter
23
Saturn
360
Uranus
Neptune
11
Pluto
0.4
9Jb3 Getting into space
The Apollo spacecraft that went to the Moon were launched by Saturn V (Saturn 'five') rockets. The rockets were in three stages. Each stage included rocket engines and fuel tanks. As the fuel in each stage was used up, the empty tanks and engines were dropped to make the mass of the spacecraft lighter.
This graph shows how the mass of the rocket changed as it climbed into orbit and set off towards the Moon.
1 The following statements describe what is happening at each place on the graph. Match each statement with one of the letters on the graph, and copy them out in the correct order.
The mass decreases as the fuel and oxygen in the second stage is used up.
The fuel in the third stage has now been used up to send the spacecraft towards the Moon.
The mass is decreasing as the fuel and oxygen in the first stage is used up.
Some of the fuel in the third stage has been used up to get the spacecraft into orbit.
The mass changes suddenly when the first stage is dropped.
This is the mass of the rocket before it is launched.
The mass changes suddenly when the second stage is dropped.
The mass is less here because the third stage has been dropped. The mass is not changing because the spacecraft does not need to use any more fuel until it reaches the Moon.
The spacecraft does not need fuel to stay in orbit, so its mass is still the same three orbits later.
2 a What is the mass of the rocket and Apollo at launch?
b What is its weight at launch? (Hint: Gravity = 10 N/kg; there are 1000 kg in 1 tonne.)
3 a What is the mass of the spacecraft when it is in orbit around the Moon?
b What would its weight be if gravity was still 10 N/kg?
c Will its weight be more or less than the answer you gave to part b? Explain your answer.
4 Why doesn't the spacecraft need to use its engines while it is in orbit?
5 The first stage of the Saturn V produces more than seven times the thrust of the second stage.
a Why do you think that it was designed this way?
b How could you tell from the graph that the first stage produces the most force?
9Jb4 Space exploration
Use reference books, CD-ROMs or the internet to find out about the history of the human exploration of space. Use your findings to make an illustrated timeline showing some of the most important people and events.
There are some suggestions below to help you to get started.
You could look up these space missions or spacecraft:
- Vostok, Voskhod, Mercury, Gemini, Apollo, Skylab, Buran, Mir, Space Shuttle, International Space Station
You could find out about these people:
- Yuri Gagarin, Alan Shepard, Alexei Leonov, Valentina Tereshkova, Neil Armstrong, James Lovell, Helen Sharman
You could find out about these events:
- The first person in space, the first spacewalk, the first woman in space, the first person to land on the Moon
[ literacy, research ]
9Jb5 The Vomit Comet
You have probably seen pictures of astronauts floating around in the Space Shuttle. When astronauts are floating around like this, people often refer to them as being 'weightless', or being in 'zero gravity', but this is not correct.
At the altitude that the Space Shuttle orbits, gravity is pulling on every kilogram of mass with over 9 N of force. Gravity is still pulling on the astronauts, so they still have weight. So why do they feel weightless?
When you are standing on the ground, gravity is trying to pull you downwards. You can't go down, because the ground is in the way. If you went into orbit around the Earth, your spacecraft would be 'falling' around the Earth, and you would be falling with it. The spacecraft is not pushing up on your feet, so you feel as if you do not have any weight. It is a bit like the feeling you get in a lift when it suddenly starts going down.
American astronauts used to be trained to cope with this weightless feeling in an aeroplane. The aeroplane would fly up and down, and during parts of the flight the trainee astronauts would feel weightless.
When the aircraft is pushing over the top of each curve, it is falling at the same speed as the people in it. They feel weightless.
1 Why do people refer to astronauts being in 'zero gravity'?
2 An astronaut has a mass of 70 kg.
a What would her weight be on Earth?
b What would be the force of gravity on her when she is in orbit?
3 Why do astronauts feel weightless when they are in orbit?
4 How are astronauts trained to cope with the feeling of weightlessness?
5 Find out:
a why the training aircraft was called the 'Vomit Comet'
b how 'zero gravity' affects the way astronauts live in space. What special arrangements have to be made for sleeping, eating and drinking, and going to the toilet?
[ knowledge, research ]
9Jc1 For and against 1
There have been lots of different ideas about the Earth and the Solar System.
1 Which statements above are observations? Write the letters in your book.
2 Which statements above are ideas about how the solar system is arranged?
3 Some people's ideas about the universe were based on their religious beliefs. Which ideas are like this?
4 Which observations show that the religious ideas are not correct?
5 Which ideas about the Solar System are based on observations?
6 Which statements support our ideas that the Earth and the other planets move in elliptical orbits around the Sun?
7 Which statement best explains why scientists believe our current idea is correct?
[ literacy ]
9Jc2 For and against 2
People have had lots of different ideas about the Earth and the Solar System, and made a lot of observations. Here are some of them:
1 a Which of the statements above are based on religious beliefs, not observations?
b Summarise these statements in your own words.
2 Use some of the statements above to write a paragraph to try to persuade someone that the statements you summarised in question 1 are not correct.
3 Which observations could support the idea that the Earth is at the centre of the Universe?
4 Use some of the statements to persuade someone that the observations in question 3 can be explained even if the Earth is not at the centre of the Universe.
5 Which observations support our current idea that the planets move in elliptical orbits around the Sun?
6 Which statement best explains why scientists believe our current idea is correct?
9Jc3 Early ideas
There have been lots of different ideas about the Earth and the Solar System. Some of these ideas are explained in the Exploring Science book, but there have been lots of other ideas as well.
What do you need to find out?
You could:
- find out what people thought about the arrangement of the stars and planets in ancient civilisations, such as ancient Greece, Egypt or India
- find out how we think the Earth and the Solar System were formed, and find out about the creation stories of other cultures and different religions.
Whichever idea you investigate, you need to find out:
- why people believed the idea
- what evidence we now have to show that the idea is not correct.
Where are you going to find your information?
- Encyclopaedias and other reference books can provide a lot of information.
- Search the Internet. You could try searching using the phrases 'creation story' or 'creation myth'.
How are you going to present your information?
- design a wall display or poster
- write an illustrated report
- give a short talk to the rest of the class
- take part in a class debate about different ideas.
Your presentation should look attractive, and present the information clearly.
[ knowledge, literacy, research ]
9Jc4 Kepler's laws
Ptolemy's model of the Universe had the Earth at the centre, with the Sun, planets and stars revolving in circular orbits around the Earth. The model could be used to predict where in the sky a planet would be at a particular time. Unfortunately, lots of adjustments to the model had to be made to make it fit the observations of the planets.
When Copernicus developed his ideas about a Sun centred Solar System, he still put his planets in circular orbits. At that time, everyone believed that the Universe was made by God, and God would only have used 'perfect' shapes like circles. Copernicus' model was a little simpler than Ptolemy's, but it still needed lots of complicated adjustments to make the predictions of the model fit the observations.
It was a long time before everyone accepted that the Sun, not the Earth, was at the centre of the Solar System. There were many reasons for this; one reason was that it was still very complicated, and another was that the Christian beliefs at the time held that the Earth was the centre of the Universe.
Copernicus' model of the Solar System, which used complicated sets of circles to describe the motion of the Earth and the other planets around the Sun.
Tycho Brahe (1546-1601) was an astronomer who worked in Denmark and Prague. He spent years making detailed observations of the positions of the planets. In 1600 he took on Johannes Kepler (1571-1630) as an assistant, and asked him to study the orbit of Mars, which was very difficult to predict using Copernicus' model.
Kepler started by working out the speed of Mars at different places around its orbit, and discovered that its speed changed. This discovery eventually led him to the idea that the orbits of the planets were ellipses, not circles. Once he worked out the orbits of the planets using this idea, his model matched observations very well. It took Kepler eight years to make all the calculations and check his theory, but his theory is now accepted by astronomers everywhere. He published his ideas in 1609.
At the time, no one knew why Kepler's ideas worked. It wasn't until Isaac Newton (1642-1727) published his ideas about gravity in 1687 that scientists could explain why the speeds of the planets changed at different places in their orbits.
Note that the orbits of the planets are almost circular - the elipse in this diagram is exaggerated.
A planet in an elliptical orbit (you will need the letters on the diagram when you answer questions 4 to 7).
1 Why wasn't Copernicus' model of the Solar system accepted by most astronomers when his ideas were first published?
2 a What did Copernicus assume about the shapes of the orbits of the planets?
b What do you think he assumed about the speeds of the planets in their orbits?
3 a When Kepler started work on the orbit of Mars, what did he start by calculating?
b How were Kepler's assumptions about orbits different to Copernicus'? (Hint: There are two ways.)
4 Make a copy of the diagram on the previous page showing a planet in an elliptical orbit.
a Draw an arrow on your diagram at A showing the direction the Sun's gravity is pulling on the planet.
b Why doesn't the planet move directly towards the Sun from point A?
c Describe the effect of the Sun's gravity on the planet at A.
d Draw an arrow like this at B on your diagram.
You can think of the pull of the Sun's gravity being partly at right angles to the orbit (represented by arrow X), and partly along the orbit (arrow Y). X and Y are called components of the force at B.
e What effect will the Y part of the force have on the speed of the planet at B?
f Draw arrows similar to the one at B for positions C to F. Show the X and Y components at each place.
g Use the information on your diagram to explain why the planet is slowing down at C.
h Use the information on your diagram to explain why the planet is speeding up at E.
[ literacy, numeracy, revision ]
9Jd1 Gravity revision
Underline the correct words in the brackets.
All objects produce a force of gravity. Small objects produce a (large/small) force, and large objects produce a (large/small) force.
The Earth is very big, so it has a (small/large) gravity force. This force pulls you (away from/towards) the Earth. The force of gravity pulling on you is your (mass/weight). The units for weight are (newtons/degrees).
The Moon is (bigger/smaller) than the Earth, so the Moon's (weight/gravity) is not as strong. If you could go to the Moon, you would weigh (more/less) than you do on the Earth.
The Sun is much (smaller/bigger) than the Earth. All the (planets/stars) are moving very fast around the Sun. The Sun's gravity stops them flying off into space.
The force of gravity on two things depends on how far apart they are. If two things are close together, they will have a (stronger/weaker) force between them than they would if they were a long way apart.
Mercury is the closest planet to the Sun, so the Sun is pulling on Mercury with a (weak/strong) force of gravity. Pluto is the planet that is (closest to/furthest from) the Sun, so the Sun's pull on Pluto is much (stronger/weaker).
The force of gravity between the different (planets/stars) in our galaxy keeps them all together.
[ knowledge, literacy ]
9Jd2 Different orbits
A satellite needs to be moving at a certain speed to stay in its orbit. If it is going too fast it will fly off into space. If it is going too slowly it will fall to Earth. The force of gravity is greatest close to a planet, so satellites that are in low orbits need to move faster than satellites in high orbits. Closer satellites also do not have as far to go, so the time they take to complete one orbit is much shorter than for satellites orbiting further out.
A satellite in a low orbit will take only a few hours to orbit the Earth. If its orbit is tilted relative to the Equator, it will move over different parts of the Earth.
When the satellite reaches this point on its next orbit, the Earth will have spun round and a different part of the Earth will be under it.
The satellite flies over different parts of the Earth on each orbit.
If the satellite is in an orbit that takes it over the North and South Poles, it will eventually cover all parts of the Earth as the Earth spins beneath it. This kind of orbit is called a polar orbit.
Some satellites are far enough from the Earth to take exactly 24 hours to complete one orbit. This means that these satellites will stay over the same place on the Earth all the time. This kind of orbit is called a geostationary orbit. Satellites in geostationary orbits are usually over the equator.
A satellite in polar orbit.
1 Look at the path of the satellite in the diagram on the first page.
a Explain why the satellite travels over different parts of the Earth on each orbit.
b What would happen to the path of the satellite if its orbit was tilted more?
2 The list below shows some different uses for satellites. For each use, say which type of orbit would be best, and explain why.
a investigating the ozone holes over the Arctic and Antarctic
b transmitting satellite TV pictures
c investigating sea temperatures in the world's oceans
d making maps of Africa and Asia
e helping to make weather forecasts for Europe
9Jd3 More about satellites
You have been asked to help your local primary school by making a small booklet or a series of posters to tell 10-year-old children about satellites.
First, think about what would interest them and what they would understand. You could:
- explain the different kinds of things that satellites can do and why they are useful in everyday life (you could include weather satellites, communications satellites, the Global Positioning System, astronomical satellites, etc.)
- describe, in simple terms, what satellites have inside them (this depends on what the satellite is for)
- tell them the history of satellites, starting with Sputnik
- explain what 'space junk' is, and why it is a problem.
Then you need to think about how you are going to present your information. It will need to look interesting, and the language will need to be clear and simple.
You should be able to find all the information you need in reference books or on the Internet. A good place to start on the internet is www.howstuffworks.com.
9Jd4 Where did the Moon come from?
The Moon is very close to the Earth, but looks very different. For centuries, astronomers have been interested in how the Moon was formed. There have been lots of theories to try to explain the origin of the Moon.
A The Moon could have been a passing asteroid that was captured by the Earth's gravity. In this case, the composition of the Moon and the Earth could be quite different.
B The Earth and Moon could have formed together from the same cloud of dust and gas. If this is what happened, the Earth and Moon would have similar compositions.
C While the Earth was forming there were a lot of other bodies flying around the Solar System. One of these could have hit the Earth and
thrown up a lot of material. If this material stayed in orbit instead of falling back to Earth, it could have joined up to form the Moon. The Moon would consist of similar materials to the Earth's mantle.
It was difficult for astronomers to work out which theory was the most likely explanation until the Apollo missions in the 1970s. The Apollo astronauts brought back samples of moon rock, which showed that the Moon contained very similar materials to the Earth's mantle. The astronauts also set up instruments to measure moonquakes, which told scientists that the Moon has a very small iron core. Its core would be smaller than the Earth's anyway, because the Moon's diameter is only 27% of the Earth's, but scientists found that the Moon's core is much smaller than they expected.
1 What two pieces of evidence do scientists have that could help them to decide which theory is correct?
2 a Draw scale diagrams to show the Earth and the Moon at their correct relative sizes.
b The Earth's core has a radius approximately 50% of the Earth's radius. Draw the core on your diagram of the Earth. Roughly estimate the size of the Moon's core, and add it to your Moon diagram.
3 Describe each of the three different theories put forward to explain the origin of the Moon. For each theory describe the evidence for and against it. Present your answer as a table.
4 Scientists think that asteroids or comets may have hit the Earth several times in the past.
a Find out and describe three different effects a large impact could have.
b Find out how Jupiter has helped to protect the Earth against impacts.
[ knowledge, considering, numeracy, research ]
9J Summary Sheets
Gravity and space
Mass and weight
The mass of something is the amount of substance or 'matter' it contains. It is measured in kilograms (kg). Weight is the force of gravity pulling on a mass. It is a force, so it is measured in newtons (N).
Gravity
Gravity is the force of attraction between two masses. The force of gravity is stronger if:
- the objects have large masses
- the objects are close together.
On Earth, the gravity pulls on every kilogram of mass with a force of 10 N.
Gravity is not as strong on the Moon, because the Moon has a much smaller mass than the Earth. If you went to the Moon your mass would not change, but your weight would be less than on Earth because the Moon's gravity is weaker.
If a rocket travels away from the Earth, the force of gravity gets less and less as it gets further from Earth. If it is heading for the Moon, it will eventually reach a place where the Earth's gravity is cancelled out by the Moon's gravity. After that, the Moon's gravity will be pulling it towards the Moon.
The Sun's gravity keeps all the planets moving in elliptical orbits around it. If there was no gravity from the Sun, the planets would all fly off into space. The Earth's gravity keeps the Moon in orbit around the Earth.
Satellites
A satellite is anything that orbits around a planet. The Moon is the only natural satellite of the Earth.
Artificial satellites can be put into orbit around the Earth. They can be used for communications (transmitting telephone calls or television programmes), for navigation, or to take pictures of the Earth or the planets and stars.
Satellites can also be put into orbit around other planets. They can take pictures and take measurements, and send all the information back to Earth.
Changing ideas about the Solar System
People have known that the Earth is spherical for thousands of years, but they have only believed that the Sun is at the centre of the Solar System for about 500 years.
Early ideas had the Earth in the centre of the Solar System, with the Sun, the planets and the stars moving in circular orbits around the Earth. These ideas were used to make predictions about where the planets would be in the sky, but the predictions were not very accurate.
Copernicus suggested that the Sun was in the centre of the Solar System, but his model still had the planets moving in circular orbits. The predictions made using this model were a bit more accurate, but there were still errors.
Kepler suggested that the planets actually move in elliptical orbits around the Sun. His model could be used to make very accurate predictions. After Newton had worked out how Kepler's model could be explained using his ideas about gravity, most scientists accepted that this was the correct way of thinking about the Solar System.
9J Target Sheet
Topic
Targets
Before the unit
I have learned this
I have revised this
9Ja
Know what causes weight.
2
Know which direction 'down' is.
Know how gravity affects objects.
Know how to work out the weight of an object.
9Jb
Know why gravity is different on other planets.
Know how to calculate weight on other planets.
Know how gravity changes with distance.
Know how changing gravity affects spacecraft.
9Jc
Know about some early ideas about the Solar System.
Know how our modern ideas are different to the early ideas.
Understand our current model of the Solar System.
Know some of the evidence for our current model of the Solar System.
9Jd
Know why planets stay in their orbits.
Know what a satellite is.
Know of some uses of artificial satellites.
Know about different kinds of orbits for artificial satellites, and why they are useful.
9J Word Sheets
Word sheets that include new words from the 'Focus on:' pages are available on the Exploring Science website.
9Ja - Gravity and weight/Newton and gravity
Word
Pronunciation
Meaning
gravity
The force of attraction between any two objects.
newton (N)
The unit of force.
weight
The amount of force with which gravity pulls something towards the Earth. It is measured in newtons (N).
9Jb - Going to the Moon
There are no glossary definitions in this topic.
9Jc - Changing ideas
9Jd - The Sun pulls/Satellites/Going further out
artificial satellite
A satellite made by humans.
communications
A satellite used to transmit TV programmes or telephone calls.
satellite
Earth observation
A satellite used to take pictures of the Earth - for instance to help forecast
the weather.
elliptical
e-lip-tick-al
Oval shaped. The shape of a planet's orbit around the Sun.
geostationary orbit
An orbit where a satellite takes exactly 24 hours to circle the Earth, so it always stays over the same part of the Earth.
natural satellite
A satellite that has not been made by humans. The Moon is a natural satellite of the Earth.
polar orbit
An orbit where a satellite passes over the North and South Poles. It will pass over all parts of the Earth during several orbits.
Anything in orbit around a planet.