1) Gravity is an attractive force that depends on the mass of objects and the distance between them. It affects anything with mass. 2) On Earth, gravitational field strength is 10N/kg. An object's weight is calculated by multiplying its mass by gravitational field strength. Some examples of weight calculations on Earth are provided. 3) When a rocket launches from Earth, the force needed to accelerate it decreases as it gains distance from Earth and loses mass by burning fuel, both of which decrease the gravitational force pulling it downwards.

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Gravity and SpaceGravity and Space

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GravityGravity
Gravity is an attractive force that affects anything with mass:
Note that this
force goes both
ways – the Earth
is attracted to us.

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GravityGravity
Gravity 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

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Weight vs. MassWeight vs. Mass
Earth’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?

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RocketsRockets
When 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

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Natural SatellitesNatural Satellites
Mercury
Mars
Jupiter
Saturn
Neptune
Uranus
Pluto
Venus
Earth
These planets are all
satellites of the sun

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Artificial SatellitesArtificial 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