Gravity and Space

GravityGravity is an attractive force that affects anything with mass:

Note that this force goes both ways – the Earth

is attracted to us.

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

Gravity (in Detail)The amount of gravity attracting an object decreases the further out the object is…

If you double the distance the gravitational force divides by 4

If you triple the distance the force divides by 9

Menu

Weight vs. MassEarth’s Gravitational Field Strength is 10N/kg. In other

words, a 1kg mass is pulled downwards by a force of 10N.

W

gM

Weight = Mass x Gravitational Field Strength

(in N) (in kg) (in N/kg)

1) What is the weight on Earth of a book with mass 2kg?

2) What is the weight on Earth of an apple with mass 100g?

3) Dave weighs 700N. What is his mass?

4) On the moon the gravitational field strength is 1.6N/kg. What will Dave weigh if he stands on the moon?

RocketsWhen a rocket flies away from Earth the force needed to keep it accelerating decreases:

This is because…1) As the rocket gets further away from Earth the force of ______ decreases.

2) As the rocket burns fuel it gets _______, also decreasing the gravity downwards.

Words – gravity, smaller, large, lighter

_____ force needed here

_____ force needed here

Natural Satellites

Mercury

MarsJupiter

Saturn

Neptune

Uranus

Pluto

VenusEarth

These planets are all satellites of the sun

SatellitesA satellite is anything that orbits something else. The Earth has a natural satellite (– the moon). The Earth has hundreds of artificial satellites orbiting around it.

All satellites need two things in order to stay in orbit:

• Gravity

• High speed

Artificial Satellites

1) Observation (e.g. Hubble Space Telescope) – these are in orbit high above the Earth and can observe the universe without interference by the ____________

2) Communications (e.g. ___, phone, car “SatNav” systems) – these satellites are in “geostationary” orbits. This means that the satellite always stays above ____ ____ point on the Earth and takes a ______ to complete an orbit

3) Monitoring (e.g. weather, spy satellites) – these satellites have a “___ _____” orbit and may scan around the Earth several times a day

Artificial satellites have been around for 50 years and have 3 main uses:

Words – the same, atmosphere, low polar, TV, day

Solar Systems, Galaxies and the UniverseOUR SUN is one of millions of stars that orbit the centre of…

THE MILKY WAY (which is one of a billion galaxies that orbit AND move away from the centre of…)THE UNIVERSE

What Can We Use Satellites For?1) Observation (e.g. Hubble Space Telescope) – these are in orbit high above the Earth and can observe the universe without interference by the atmosphere.

It can take pictures like this….. Each swirl (and there are LOTS in this picture) is a GALAXY!