The earth exerts a force on everything
 This force is called gravity
 What does gravity do?
 Hold your pen up and then let go
 Why does this happen
The force the earth exerts on me is
called my weigh
The weight of a body is the force pulling
it towards the center of the earth
Like all forces, weight is measured in
So what is your weight, how do you
measure your weight
 We are all made of matter,
people have a grater matter than others
 The more matter an object has the
greater will be the force acting on it
A block of lead would have a greater
mass than a block of wood of equal size
Force of gravity acting on the block of
lead would be greater than the force of
gravity acting on the block of wood.
The block of lead has a greater weight
So the weight of a object is determined
by two things the mass of it, and the
fore of gravity acting on it
Does your weight change when your in the
moon or space
Your weight changed because the pull of
gravity on it changes
What is weight again = The force the earth
exerts on an object
Will a litre of milk weigh the same on the
earth, moon and space
The litre of milk will be 6
times lighter on the moon
compared to earth
The moon is one-sixth the
size of the earth
The force of gravity acting on
an object is one-sixth, of the
force acting on earth
The moon has a force of 1.67
on 1kg
The litre of milk will be weightless in space
Your weight is zero in space, that’s why you
can float because there is no force of gravity
acting on you
Things also wheigh less on the top of a
 Instead of a force of 10 N it would be 9 N
Class Activity
Do calculation 1, 2, 3, 6,
 6 minutes
Calculations 4, 5 homework
Calculations 1
A litre of milk (1kg) on the earth weighs
1kg x 10N = 10 N/kg
 A litre of milk on the moon weighs
1 kg x 1.67N = 1.67 N/Kg
 A litre of milk in space weights
1 kg x 0 = 0 N/kg
 A litre of milk on the top of a mountain weighs
1 kg x 9N = 9 N/Kg
Calculation 2
What is the object weighed 600kg, what
would it weigh
 Earth= 600 kg x 10N = 6000 kg/N
 Moon= 600 kg x 1.67N = 1002 kg/N
 Space= 600 kg x 0N = 0 kg/N
 Mountain= 600 kg x 9N = 5400 kg/N
Is it still milk inside
Is it still a litre
So this states that mass stays the same
If you are standing on the earth , moon
and space you have the same mass but
your weight changes
Recap = Mass & Weight
 Measured in Newtons
 Measured in
kilograms (kg)
 Varies, depends on
 Is fixed, never
where you are
 Is a force or a pull on
 Is a fixed property of something
all things, like length
or volume
Calculation 3
 An
object of mass 50 kg has a
weight of ___________ on earth
 1kg
= 10 N
 50 kg = 500N
 Answer 500N
Calculation 6
The mass of a man who weighs 550 N
on earth is ___________
1 kg = 10 N
 ? Kg = 550N
 Answer 55 kg
Where would I weigh more?
Long Jump Record
Why did Bob
Beaman’s 1972 long
jump record (8.9
metres) last until
 The Olympics were
held in Mexico
city….he weighed
 Homework
calculations 4 and 5
An astronaut has a mass of 124 kg
His weight on earth is 1240 kg/N, on the
moon is 207.08 kg/N and inouter space
is 0 kg/N. His mass , unlike his weight
never varies wherever he is
Calculating Weight 5
Find the weight of a 250g bag of biscuits
First change the mass to kg
250g = 0.25 kg (250g ÷ 1000)
Now, F = 0.25kg * 10 m/s2
= 2.5 kg/m2
= 2.5 N
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