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9.9 Option – Space science: 2. Gravity varies at different places

Syllabus reference (October 2002 version)
2. The strength of gravity varies at different points in space	Students learn to: identify the relationship between mass and gravitational pull and relate this to the revolution of the Moon around Earth and the revolution of the planets around the Sun. identify situations on Earth where one could experience ‘weightlessness’ discuss the reasons for the apparent weightlessness of an object in orbit	Students: gather, process and present information from secondary sources to identify and discuss the reasons why animals have been sent into space before humans

Syllabus reference (October 2002 version)

2. The strength of gravity varies at different points in space

Students learn to:

identify the relationship between mass and gravitational pull and relate this to the revolution of the Moon around Earth and the revolution of the planets around the Sun.

identify situations on Earth where one could experience ‘weightlessness’

discuss the reasons for the apparent weightlessness of an object in orbit

Students:

gather, process and present information from secondary sources to identify and discuss the reasons why animals have been sent into space before humans

Extract from Senior Science Stage 6 Syllabus (Amended October 2002) © Board of Studies, NSW.
[Edit: 16 Sept 08]

Prior learning: Science Stages 4 – 5 Syllabus. 4.6.2, 4.6.10 and 5.6.6 a)

Background: Scientists don’t fully understand gravity but they know that every object exerts a gravitational pull on every other object according to the mass of the objects. Small objects like people have such a small mass that the gravitational pull they exert is negligible but large objects like the Earth have a considerable gravitational force on small objects and this force causes the Moon to revolve around the Earth.

identify the relationship between mass and gravitational pull and relate this to the revolution of the Moon around Earth and the revolution of the planets around the Sun.

The gravitational pull of the Earth on the Moon is determined by the mass of the Earth times the mass of the moon divided by the distance between the two squared

The Earth is much more massive than the Moon so it has a greater gravitational pull than the Moon has on the Earth. Therefore the Moon revolves around the Earth and not the other way around.

Similarly the Sun is so massive (about 98% of the mass of the solar system) that its gravitational pull is very great. Not only does the Earth orbit around the Sun but so do all the planets, including tiny Pluto at 5.9 X 10⁹ kilometres from the Sun.

gather, process and present information from secondary sources to identify and discuss the reasons why animals have been sent into space before humans

Gather information from popular science journals such as Sky and Space and New Scientist, look on the internet by going to search engines such as google.com or dogpile.com and then typing in Sputnik 2 and Laika. Many libraries also have articles from newspapers of the day. You could check papers like the Sydney Morning Herald, The Australian and the Daily Telegraph.

Process the information by setting it out so that the information from different sources can be compared for reliability and validity. Take the information that you believe is the most accurate and organise it for your presentation.

Present the information in a succinct form so it is easy to understand and present to the class. If you are doing an oral presentation you may like to use overheads, including of photographs or drawings. In your presentation give the reasons that you have deduced from the information gathered, on why animals have been sent into space before humans.

Some background information

The Russians were the first to send a rocket into space. The Americans and Russians were having a race to see who could be first to do things related to space. It was very early in space research so they weren’t sure of the technology. Some questions they were testing were- Would the pressure be OK? Would the oxygen supply be correct? Sputnik 2 launched in 1957 had the dog Laika on board. There were other flights that had animals on board as well. Try finding more information from your resources.

identify situations on earth where one could experience ‘weightlessness’.

When an object is in free fall it is weightless for the time it is falling. An example would be when a parachutist jumps out of a plane and is falling before she pulls the cord.

discuss the reasons for the apparent weightlessness of an object in orbit

Weightlessness means that an object has no weight at all. As you get further away from the Earth in a space ship the force of gravity acting on you gets less and less but it does not reach zero.

It is sometimes claimed that astronauts in space are in a "zero gravity" environment, but actually they are still very much under the influence of the Earth's gravity. The astronaut observes no tendency at all to fall towards Earth, but it isn’t due to zero gravity. The force of gravity is perfectly balanced by the centrifugal force.

Introduction to microgravity Microgravity.com, NASA

Apparent Weightlessness Benjamin Crowell, Lectures in Physics, free eBook, USA