The document discusses gravity as an attractive force affecting objects with mass and explains how it varies based on mass and distance. It details the equations for calculating weight, gravitational field strengths, and how rocket propulsion changes as they ascend. Additionally, it describes the functions of natural and artificial satellites, including their roles in observation, communication, and monitoring.

1. 03/07/12
Gravity and Space

2. Gravity
03/07/12
Gravity is an attractive force that affects anything with mass:
Note that this
force goes both
ways – the Earth
is attracted to us.

3. Gravity
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If you double the
Gravity depends on 2 things: mass of one object
you double the force
1) The mass of
the objects
F 2F
2) The distance between them
If you double the
F distance the gravitational
force divides by 4…
F/4

4. Weight vs. Mass
03/07/12
Earth’s Gravitational Field Strength is 10N/kg. In other
words, a 1kg mass is pulled downwards by a force of 10N.
W
Weight = Mass x Gravitational Field Strength
(in N) (in kg) (in N/kg)
M g
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?

5. Rockets
03/07/12
When a rocket flies away from Earth
the force needed to keep it
accelerating decreases: _____ force
needed here
_____ force
needed here
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

6. Natural Satellites
03/07/12
Mercury These planets are all
Venus satellites of the sun
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto

7. Artificial Satellites
03/07/12
Artificial satellites have been around for 50 years and have 3 main uses:
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 3) Monitoring (e.g.
that the satellite always stays above weather, spy
____ ____ point on the Earth and takes satellites) – these
a ______ to complete an orbit satellites have a
“___ _____” orbit
and may scan
around the Earth
several times a day
Words – the same, atmosphere, low polar, TV, day