1. P3 1.6 Gravitational attraction
L/O Explain:
1. The difference between
mass and weight.
2. How gravitational force acts.
What is gravity?
* a small force of attraction exists between any two objects,

2. P3 1.6 Gravitational attraction
L/O Explain:
1. The difference between
mass and weight.
2. How gravitational force acts.
What is gravity?
* a small force of attraction exists between any two objects,
* the force gets weaker with increased separation.
* the force gets larger as the objects get larger.

3. The pull of gravity L/O Explain: 1. The difference between
mass and weight.
2. How gravitational force acts.
Mass is how much matter an object is made of.
It is measured in kilograms. Kg
Mass does not change in different places.
( Mr G. is 80 Kg on the earth / Moon/ outer space)
Weight is the force of gravity acting on an object. Units: N
It is 1/6 on the moon and nothing at all in outer space!
Weight on Earth (N) = mass (kg) x 10 N/kg

4. GRAVITY AND SPACE
10 N
The Earth’s gravity attracts every object on or near the Earth.
It tries to pull them towards the centre of the Earth.
The Earth pulls every kilogram with a force of 10 Newtons.
Another way of saying this is to say the Earth’s gravity has a strength of 10 N/kg or that 1 kg weighs 10 N.
How much would a girl with a mass of 40kg weigh on Earth?
40 x 10 = 400 N
1 kg

5. 50kg
50kg

6. GRAVITY AND SPACE
Different planets, stars and moons have different gravitational strengths.
The moon has a gravitational strength of about 1.6 N/kg.
This means that every kilogram weighs only 1.6 N on the Moon.
How much would a girl with a mass of 40 kg weigh on the Moon?
40 x 1.6 = 64 N
Jupiter has a gravitational strength of about 20 N/kg.
How much would the same girl weigh on Jupiter?
40 x 20 = 800 N

7. On a larger planet you weigh more because
On Earth the gravitational field strength
is 10 newtons per kilogram
Planet
Earth
Mars
Jupiter
Pluto
Mass /Kg 1 1 1 1
Gravitational
field strength
N/kg 10 4 26
0.5
Weight of 2 kg
bag of sugar 20 8 52 1
On a larger planet you weigh more because
the force of gravity is greater
Black hole ‘singularity’ ?

8. GRAVITY AND SPACE
What does the strength of the gravitational pull between two objects depend on?
Their mass.
How far apart they are.
What does an object’s weight depend on?
Its mass.
The strength of gravity.

9. Value at Earth’s surface

10. For anything to go in a circle there has to be a force.
Otherwise they would…
….. continue in a straight line
out of the solar system

11. Gravitational attraction
Calculating your weight

12. Calculating your weight
weight = mass  gravitational field strength
On Earth, the gravitational field strength is 10 N/kg.
So if your mass is 50 kg, your weight on Earth is =

13. Calculating your weight
weight = mass  gravitational field strength
On Earth, the gravitational field strength is 10 N/kg.
So if your mass is 50 kg, your weight on Earth is
= 50 kg  10 N/kg
= N

14. Calculating your weight
weight = mass  gravitational field strength
On the Moon, the gravitational field strength
is 1.6 N/kg.
So if your mass is 50 kg, your weight on the Moon is
= 50 kg  1.6 N/kg
= 80 N

15. Calculating mass
On Mars, the gravitational field strength is 3.7 N/kg.
The average Martian weighs 111 N.
What is its mass?
weight = mass  gravitational field strength
So 111 N = mass  3.7 N/kg
mass = 111 N ÷ 3.7 N/kg
= 30 kg

19. Lift off !
For a rocket to lift off the ground:

20. For a rocket to lift off the ground:
Thrust = 3.2 million N
For a rocket to lift off the ground:
Weight = 3.0 million N

21. For a rocket to lift off the ground:
Thrust = 3.2 million N
For a rocket to lift off the ground:
Thrust is larger than the weight
Weight = 3.0 million N

22. For a rocket to lift off the ground:
Thrust = 3.2 million N
For a rocket to lift off the ground:
Thrust is larger than the weight
Resultant force
( force left over for acceleration) =
Weight = 3.0 million N

23. For a rocket to lift off the ground:
Thrust = 3.2 million N
For a rocket to lift off the ground:
Thrust is larger than the weight
Resultant force
( force left over for acceleration)
= million N million N
= million N
( 200,000 N)
Weight = 3.0 million N

24. sun
sun M V E M J S U N P

25. gravity
gravity
the cork would
fly off at a tangent

26. mass weight gravity gravity orbit sun i) Mass stays the same
ii) Weigh more on take off
Weigh nothing in space
Weigh 1/6 on the moon

27. Check your learning Which of these statements about gravity are true?
On the Moon a feather and
a hammer would fall at the same
rate because there is no air
resistance on the Moon.
On Earth a feather will fall more
slowly than a hammer because
gravity has less effect on it.
On Earth a feather will fall
more slowly than a hammer
because air resistance has
a greater effect on the feather.
A feather and a hammer
would float on the Moon
because there is no gravity
on the Moon.
On the Moon a feather will fall
more slowly than a hammer because gravity has less effect on it.

28. Check your learning - answers
The true statements are in purple.
On the Moon a feather and
a hammer would fall at the same
rate because there is no air
resistance on the Moon.
On Earth a feather will fall more
slowly than a hammer because
gravity has less effect on it.
On Earth a feather will fall
more slowly than a hammer
because air resistance has
a greater effect on the feather.
A feather and a hammer
would float on the Moon
because there is no gravity
on the Moon.
On the Moon a feather will fall
more slowly than a hammer because gravity has less effect on it.