Objectives

1
Gravity and Space

• Objectives
• To understand
• what gravity, mass and weight are.
• how gravity changes.
• how the weight changes of an object.
• what affects gravity.
• orbits of planets and satellites.

2
Gravity, Mass and Weight

• What do gravity, mass and weight all have in
  common?
• Forces can
• Change speed of an object
• Change direction of object
• Change the size or shape of an object

FORCES
3
Gravity

• Force of attraction between 2 masses.
• Not just on Earth but everywhere
• It can only pull not push.
• Acts towards centre of Earth.

4
Mass

• Amount of MATTER in an object.

Not to scale
4 kg
0.1 kg

• Measured in kilograms (kg).

• Stays the same anywhere you go.

5
Weight

• A downward-pulling force on an object due to
  gravity.
• Measured in Newtons (N)
• Changes depending on where you are.
• Where would the flag be lighter?

On Earth On Moon
6
Calculating Weight and Mass

• In order to calculate mass or weight of an object
  you need the gravitational field strength.
• On Earth it is approx 10 N/kg

WEIGHT MASS x G.F.S (N) (kg) (N/kg)
You need to remember this!!
7

• Calculate the mass of a book which has a weight
  of 10N.
• Calculate the mass of a man who has a weight of
  750N.
• What is the weight of a pushchair which has a
  mass of 7kg?

REMEMBER the gravitational force strength is
10N/kg on Earth.
WEIGHT MASS x G.F.S (N) (kg)
(N/kg)
8
How does Gravity change?

• What is gravity again?

• The force of attraction between 2 masses
  decreases as you go further apart.

• The force of attraction for a larger object is
  greater than smaller one.

• The g.f.s changes on different planets.

9
Sir Isaac Newton

• Newton said the moon is caught between 2 forces
• Gravity
• Centrifugal force

10
Orbits

• As planets get further away from Sun
• The speed the planet moves .
• The time to complete an orbit .

11
Satellites

• Polar satellites e.g. weather. Travel in low
  polar orbit.
• They pass continuously over north and south poles.

• Geostationary satellites e.g. comunication and
  navigation.
• Travel at same speed as Earth.

12
Comets