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P3 1.6 Gravitational attraction
What is gravity?
* a small force of attraction exists between any two objects,
L/O Explain:1. The difference between mass and weight.2. How gravitational force acts.
P3 1.6 Gravitational attraction
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.
L/O Explain:1. The difference between mass and weight.2. How gravitational force acts.
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
Weight is the force of gravity acting on an object. Units: NIt is 1/6 on the moon and nothing at all in outer space!
Weight on Earth (N) = mass (kg) x 10 N/kg
Mass does not change in different places. ( Mr G. is 80 Kg on the earth / Moon/ outer space)
GRAVITY AND SPACE
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
10 N
1 kg
50kg 50kg
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
GRAVITY AND SPACE
Planet Earth Mars Jupiter Pluto
Mass /Kg
Gravitational field strength N/kg
1 1 1 1
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
On Earth the gravitational field strength is 10 newtons per kilogram
Black hole ‘singularity’ ?
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.
GRAVITY AND SPACE
g vs. r
0.002.004.006.008.00
10.0012.00
0 10000 20000 30000 40000
r in km
g i
n N
/kg
Value at Earth’s surface
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
Gravitational attraction
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
=
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
= 500 N
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
Calculating your weight
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
Lift off !
For a rocket to lift off the ground:
Lift off !
For a rocket to lift off the ground:
Weight = 3.0 million N
Thrust = 3.2 million N
Lift off !
For a rocket to lift off the ground:
Thrust is larger than the weight
Weight = 3.0 million N
Thrust = 3.2 million N
Lift off !
For a rocket to lift off the ground:
Thrust is larger than the weight
Weight = 3.0 million N
Thrust = 3.2 million N
Resultant force( force left over for acceleration)
=
Lift off !
For a rocket to lift off the ground:
Thrust is larger than the weight
Weight = 3.0 million N
Thrust = 3.2 million N
Resultant force( force left over for acceleration)
= 3.2 million N - 3.0 million N
= 0.2 million N ( 200,000 N)
sun
sun
M V E M J S U N P
gravity
gravity
the cork would fly off at a tangent
massweight
gravity
gravity
orbitsun
i) Mass stays the same
ii) Weigh more on take off Weigh nothing in space Weigh 1/6 on the moon
Which of these statements about gravity are true?
On Earth a feather will fall more slowly than a hammer because gravity has less effect on it.
A feather and a hammerwould float on the Moon
because there is no gravity on the Moon.
On the Moon a feather and a hammer would fall at the same
rate because there is no air resistance on the Moon.
On the Moon a feather will fallmore slowly than a hammer because
gravity has less effect on it.
On Earth a feather will fall more slowly than a hammerbecause air resistance hasa greater effect on the feather.
Check your learning
The true statements are in purple.
On Earth a feather will fall more slowly than a hammer because
gravity has less effect on it.
A feather and a hammerwould float on the Moon
because there is no gravity on the Moon.
On the Moon a feather and a hammer would fall at the same
rate because there is no air resistance on the Moon.
On the Moon a feather will fallmore 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 hasa greater effect on the feather.
Check your learning - answers
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