Good Science Victorian Curriculum Year 7

PHYSICAL SCIENCES
8.6
GRAVITY
LEARNING INTENTION
At the end of this lesson I will be
able to understand how Earth’s
gravity pulls objects towards the
centre of Earth.
KEY TERMS
gravitational force
the force that attracts physical
objects with mass towards
each other
weight
the force of a gravitational field
on the mass of a body
LITERACY LINK
SPEAKING
Using your own words, explain
to a partner the difference
between mass and weight. Then
swap roles, with your partner
describing the factors that affect
the size of a gravitational force.
NUMERACY LINK
MEASUREMENT
Ask your teacher for a scale to
accurately measure the mass
of your pencil case. Convert this
mass to weight by multiplying
by 9.807. Make sure to give your
answer in newtons (N).
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Every object in the universe is made of matter and has mass.
This means it creates gravity, which attracts other objects.
The larger the object, the stronger its gravitational attraction
to other objects. The closer two objects are, the greater the
gravitational force acting on each one.
Gravitational forces act towards the centre of the object
that creates them. That’s why, no matter where you are on
Earth, all objects fall towards Earth’s centre.
Gravity is always an attractive force
All objects with mass have a gravitational force that attracts other
objects towards it. The size of this force depends on two things: the mass
of the object generating it and the distance between the two objects.
Although the size of gravitational force varies, the direction does not.
Any force due to gravity will always be an attractive force. This means
that it pulls objects towards the centre of whatever mass generates the
gravitational force.
Whenever you drop something, it falls to the ground, wherever you
are in the world, because the attractive force is directed to the centre
of Earth’s mass. Why Earth? Because it’s by far the most massive object
that affects us every day. The Sun is much more massive, but is so
far away that it has little effect on people and objects compared to
Earth’s gravity.
Do gravitational forces push, pull or twist objects?
Gravitational forces change with distance
The gravitational force between two objects depends partly on their
distance from one another. Two rocks floating in space one metre
apart will have a greater attraction to each other than if they were
100 metres apart.
On Earth’s surface, gravity is constant
because the distance from the centre of
Earth is about the same everywhere.
The gravitational force of Earth
always acts towards the centre of
the planet. If an object moves
further away from Earth, such
as spacecraft flying to the
International Space Station,
the gravitational force from
Earth is much smaller.
Figure 8.7 Because these
astronauts are far away from
Earth, the gravitational force
on them is much less.
130 GOOD SCIENCE VICTORIAN CURRICULUM 7