Space
Gravity and Weight.
Key Misconceptions
• Gravity
• Weight
• The Earth
• Day and Night
• The Earth, Moon and Sun
• The Phases of the Moon and Eclipses
• The Changing Year
Misconceptions of Gravity
• Gravity is connected with air pressure and we
are in an atmospheric shield which prevents
things from floating away.
• Therefore there's no gravity in space or on the
moon.
• Gravity is associated with rotation. If the Earth
stopped spinning we’d all fly off.
• Gravity reduces with as distance between
objects increases. True but most believe it
reduces a lot sooner than is actually the case.
• Alternatively, gravity is only present on the
surface. Hence birds can fly as there is no
gravity as they aren't touching the surface.
Misconceptions of Weight
• It is possible to have
weight without
gravity.
• Weight isn't a force.
• Astronauts where
moon boots to give
then weight where
there is no gravity
Misconceptions of Falling
• Students may think that
things ‘just fall naturally’.
• Or the person letting them
go causes the force.
• Heavier things fall to
Earth faster.
Misconceptions of
Gravity In Space
• Bound in with air
pressure - no air no
gravity.
• Gravity needs a
medium, ‘molecules
of gravity’ in air.
• Possible Sci-Fi has
and weightlessness has
contributed to this.
Teaching Gravity.
• What do you think gravity is?
• Try explaining it to someone who has never
heard of it before.
Sir Isaac Newton.
• He was a scientist who was
interested in forces and
gravity.
• He did not discover gravity
and its effects existed long
before Newton.
• He did discover how to
calculate the force of gravity
on objects
• Hence the force measured in
Newtons.
On the Earth, gravity pulls with a force of 10 N on every
kilogram of mass. To find the weight of a particular mass,
multiply the mass by 10. If you know the weight and want to
find the mass, divide by 10.
Fill in the gaps in this table.
Object Mass (kg) Weight (N)
Television 8.0
Radio 1.5
Chair 50
Bag of sugar 1.0
Bottle of pop 20
Now try these….
Object Mass (g) Mass (kg) Weight (N)
Jar of jam 340 0.34 3.4
Bag of pasta 500
Tin of beans 450
Loaf of bread 800
Can of pop 330
Why don’t people in Australia
feel like they are upside down?
Gravity and Mass.
• Gravity is an attractive force that acts between all
objects that have mass. The size of the force depends on
the mass of the object.
• All objects produce a gravitational force. This is a
massive force for huge masses such as planets.
• Think about it - When you jump, the gravitational force
of the Earth pulls you down . Your gravitational force is
also pulling the Earth towards you - you just don’t
notice this effect because your mass is so much smaller
than Earth’s!
Gravity and Distance.
• Gravitational force also
depends on distance
between objects.
• Spacecraft produce a very
large force, called thrust, to
overcome the force of
gravity.
• As a spacecraft gets further
away from Earth, the force
of gravity gets smaller.
How does the gravity on the
moon differ to the gravity on
Earth?
Why?
Spacecraft and gravity
• Diagrams showing the path
of spacecraft past multiple
planets/sun show effect of
gravity on trajectory.
• Multi-planet maps can be
used to demonstarte
differing pull between
different sized objects.
Weight , Mass and Gravity on the
Moon.
• The force of gravity is less on the
Moon than on Earth. This is
because the moon has a smaller
mass than the Earth.
• Therefore any object will weigh
less on the Moon than on Earth.
• An Astronaut could jump 20 feet
in to the air on the Moon because
gravity is less.
• However, the astronaut still has
the same body and mass. He just
weighs less because gravity is
weaker on the Moon.
Talking about weight and mass.
• A scientist should never say:
“She/he weighs 50 kilograms,”
• but should always say:
“She/he has a mass of 50 kilograms,”
• Alternatively, the scientist could say:
“The gravitational force acting on her/his mass is about 500
Newtons.”
• This is the same as saying:
“His/her weight is about 500 Newtons.”
Experiments.
• Dropping two similar
sized objects to see
which lands first.
‘Feather and a steel
ball’
• Alternatively use
the IOP tennis ball
example.
http://www.youtube.com/
watch?v=PE81zGhnb0w
Experiments.
• Some free to download
games looking at how
spacecraft paths use
gravitational slingshots
Experiments.
• Use a cup full of water
(over a bucket!) to
demonstrate that cup and
water fall at same rate.
• Drill holes in the cup to
show that water stops
flowing out when in
freefall.
And of course, songs!
