Download Gravity Workshop - National Schools` Observatory

Gravity Simulation
Gravity
 Gravity is the weakest of the four fundamental
forces.
 Gravity is responsible for the attraction of
massive bodies.
 Gravitational force is always attractive and acts
along the line joining the centres of mass.
 Gravitational force is responsible for the
formation of planets, stars and galaxies.
 Gravity decides the orbital paths of the planets
and moons in our solar system.
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Newton’s Law of Universal Gravitation
 The gravitational force between the two
masses m1 and m2 is described by
Newton’s Law of Universal Gravitation.
 G is the universal gravitation constant.
 This relationship is an example of an
inverse square law force.
 Forces are equal in size but in opposite
directions.
m1  m2
F1  F2  G
2
r
G  6.67 1011 Nm2 / kg 2
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Setting up the Experiment
• This learning scenario requires flash
player 10.
•Go to http://get.adobe.com/flashplayer/
to download and install this software.
•Extract the gravitysim.zip.
• Run gravitysim.swf.
•To carry out the experiment you will also
need a stopwatch.
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The Experiment
 Drop the ball from a set distance and
measure the time it takes to hit the bottom of
the box.
 Repeat your measurements several times
and record them on the worksheet.
 Repeat for each of the nine environments
which have gravity.
 Experiment with how the ball reacts in each
of the environments by throwing the ball
with the mouse and note how this differs
from Earth.
 Analyse the results to obtain the value of the
acceleration due to gravity for each planet.
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Analysing the Results
 Values for the release height and the time
taken to fall can be used to calculate the
acceleration due to gravity for each of the
planets.
 If it assumed that there is no air resistance
and no other downward force, the
acceleration due to gravity g is equal to a.
Eq.1
Where:
 Since the ball has no initial velocity, u = 0,
the displacement, S, can be treated as the
drop height, h.
Eq.2
 (Eq.1) can then be rearranged to allow
calculation of the acceleration due to
gravity (Eq.2).
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Where:
1 2
S  ut  at
2
S = Displacement
u = Initial velocity
a = Acceleration
t = Time
2h
g 2
t
h = Drop height
g = acceleration due
to gravity
t = Time
Discussion after Experiment
 In terms of gravity, which of the
environments are most like Earth and
which are the most different?
 Why does gravity vary on other planets?
 Was the gravity more difficult to measure
on some planets more than others?
 What are the sources of error?
 Was there more variation in your results
in certain environments?
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Questions, Exercises and Tasks
 Use the internet to find the difference in the
diameter of Uranus and Earth? Given the
large difference in diameter, why is the
gravity relatively similar?
 If a man weighs 80Kg on Earth, how much
will he weigh on the other planets in the
Solar System?
 Look up the other equations of motion,
what other systems could they be applied
to?
 Investigate some of the ways that the value
of the gravitational constant, G, can be
experimentally determined.
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