Video Education America
Bringing Learning to Life
Program Support Notes
Grades 10 - College
32mins
Gravitation
Teacher Notes by Dr. John Nicholson, B. Sc.
(Hons), Dip. Ed., Ph. D., Grad. Dip. Comp. Ed.,
M. Ed.
and Roy Preece B. Sc. (Hons), Dip. Ed., Grad.
Dip. Comp.
Produced by Video Education Australasia
Commissioning Editor Christine Henderson B.Sc.
Ph.D. Dip.Ed.
Executive Producer Mark McAuliffe Dip.Art (Film &
TV) Dip.Ed. B.Ed. Ph.D.
© Video Education America
Suitable for:
Physics
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These notes can be freely copied for
classroom use only.
Gravitation
For Teachers:
Introduction
Everything and everyone in the Universe is affected by GRAVITY! Newton, the father of classical
physics, developed the Law of Universal Gravitation which is still used today to calculate the
movement of man-made satellites and the planets and stars themselves. While gravity is the weakest of
the fundamental forces it is the force binding the Universe together.
This program firstly talks of the four fundamental forces before leading into discussion of the
principles of Newton’s Law of Universal Gravitation giving examples and showing calculations that
demonstrate the concept. This leads to investigation of the motion of satellites and orbiting space
stations and finally into varying gravitational fields on different planets. The finishing touch is a
discussion as to the existence of zero gravity spaces.
This program goes beyond the mere bruising fall of an apple!
Note:
In chapter 4: ‘Gravitational Field Strength and the Inverse Square Law’, despite the vigilance of the
producer, an error exists in one frame, in the formula for gravitational field strength.
The erroreous formula: g= Gm1m2/r2 should of course be g = Gm/r2. We apologize for this error and
trust that teachers can use it to their advantage, to test their students’ powers of observation and
comprehension.
DVD Timeline
00:00:00
00:00:22
00:03:18
00:03:50
00:10:00
00:10:57
00:15:44
00:16:29
00:21:07
00:21:33
00:27:47
00:28:40
00:28:51
Start of Program
Fundamental Forces
Summary
Newton’s Law of Universal Gravitation
Summary
In Orbit 1
Summary
In Orbit 2
Summary
Gravitational Field Strength and the Inverse Square Law
Summary
Conclusion
End credits
Other Relevant Programs Available from VEA
Newton’s Laws of Motion
Please visit our website for many more relevant programs www.veavideo.com
VEA – Bringing Learning to Life
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Gravitation
Student Worksheet:
Before Viewing the Program
1.
Does gravity suck? If the Earth is spinning (once every 24 hours!) why are we not flung off into
space. Why does the Earth’s atmosphere cling to the surface?
_______________________________________________________________________________
_______________________________________________________________________________
2.
Why doesn’t the Moon just fly off into space?
_______________________________________________________________________________
_______________________________________________________________________________
3.
When the astronauts are orbiting in the space shuttle and on the space station they appear
weightless. What is meant by the term weightless?
_______________________________________________________________________________
_______________________________________________________________________________
4.
a)
What value do we use for acceleration due to gravity?
_______________________________________________________________________________
b) Where do we use this value?
_______________________________________________________________________________
c)
Is this value appropriate
• far above the Earth?
_______________________________________________________________________________
• on the Moon?
_______________________________________________________________________________
• on Mars?
_______________________________________________________________________________
5.
a)
How is the number 5.98 x 1024 best entered on your calculator? (give keys and symbols)
_______________________________________________________________________________
b) If your calculator shows an answer to a calculation as 6.2582391E11, what will you record as
the answer correct to two decimal places?
_______________________________________________________________________________
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Gravitation
While Viewing the Program
Fundamental Forces
1.
What are the four (4) fundamental forces?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
2.
Which two (2) forces act only over a very short range?
_______________________________________________________________________________
_______________________________________________________________________________
3.
Which force is the ‘weakest”?
_______________________________________________________________________________
Newton’s Law of Universal Gravitation
r
m2
m1
4.
What is the formula for the force of attraction connecting the two masses m1 and m2 together?
F = _________________________________________
5.
Explain what you understand by the meaning of “an inverse square law”.
_______________________________________________________________________________
_______________________________________________________________________________
6.
Why is the force of attraction between the Earth and ourselves so huge compared to the attraction
between two apples?
_______________________________________________________________________________
_______________________________________________________________________________
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Gravitation
7.
Calculation Question (in program) – What is the weight of a 70kg person on Mars?
G = 6.67 × 10-11 N m2 / kg2
m = 70 kg
MMoon = 6.427 × 1023 kg
RMoon = 3.41 × 106 m
F=
Gmm m Κ Κ Κ Κ × Κ Κ Κ Κ × Κ Κ Κ Κ
=
2
rm
(Κ Κ Κ Κ )2
Weight of presenter on Moon = _______________________ N
In Orbit (1)
8.
An object moving in a circle has a force acting on it towards the centre of the circle called the
___________________________________________ force.
9.
Fcentripetal = m ×
10. If the centripetal force ceases to act on a body it will travel in a _________________________ line
at constant ______________________________________.
11. What is the difference between altitude and radius?
_______________________________________________________________________________
_______________________________________________________________________________
12. Explain how to convert kph to m/s
_______________________________________________________________________________
_______________________________________________________________________________
13. Astronauts appear to be weightless when orbiting the Earth in the space shuttle. Are they
weightless? Explain.
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
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Gravitation
14. Why does the space ship stay in orbit?
_______________________________________________________________________________
_______________________________________________________________________________
15. To find an equation for the speed of a spaceship in orbit, what two quantities are equated?
_______________________________________________________________________________
_______________________________________________________________________________
In Orbit (2)
16. Why can fixed satellite dishes always pick up a signal from a satellite?
_______________________________________________________________________________
_______________________________________________________________________________
17. What is the period of a geostationary satellite?
T = ________________________ hours
T = ________________________ seconds
18.
4π 2 R 3
The period equation for a satellite is : T =
GM E
What is the period of the space station if it is orbiting at an altitude of 250 km?
T = _____________________________ seconds.
19. Calculation Question (in program) – How far from Earth is the Moon?
G = 6.67 × 10-11 N m2 / kg2
MEarth = 5.98 × 1024 kg
REarth = 6.38 × 106 m
T = 28 days
Rm
3
Rm =
GM E T 2
=
=
2
4π
__________________________________
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Gravitation
Gravitational Field Strength and the Inverse Square Law
20. a)
What happens to the gravitational field strength as you increase the radius?
_______________________________________________________________________________
_______________________________________________________________________________
b) If you move from the surface of the Earth to a point 5 Earth radii above the surface, what is
the change in the field strength?
_______________________________________________________________________________
21. a)
What is the escape speed for Earth?
_______________________________________________________________________________
b) Why does the moon have no atmosphere?
_______________________________________________________________________________
_______________________________________________________________________________
22. What is the value of gEarth? (include units!)
_______________________________________________________________________________
R (m)
g-Field
1
g
2
¼g
3
1
14
1
5
1
10
1
/9 g
/16g
/25 g
/100 g
gravitational field strength (g)
23. For the following table of values plot the graph of orbit radius (R) against gravitational field
Strength
1.00
0.80
0.60
0.40
0.20
0.00
0
2
4
6
orbital radius (m)
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8
10
Gravitation
24. Is the gravitational field strength equal to zero at the edge of the solar system (this would be way
out past Pluto)? Explain your answer.
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
25. Calculation Question – What is the escape speed for Jupiter?
vescape =
2GM
R
G = 6.67 × 10-11 N m2 / kg2
MJupiter = 1.9 × 1027 kg
RJupiter = 7.1 × 107 m
vescape = _______________ m/s
26. Why is the theoretical gravitational field strength zero at the centre of the Earth?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
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Gravitation
After Viewing the Program
1.
Is the gravitational field at the space station’s altitude equal to Zero? Do an appropriate calculation
to find out the value of “g” at an altitude of 250 km.
2.
Produce a poster, PowerPoint or similar multimedia presentation that details how satellites in
geostationary orbits are used in modern communications and information gathering.
3.
Someone once said that “flying is just falling with style and cunningly avoiding actually hitting the
ground’. Explain how this is actually how the shuttle orbits the Earth.
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
4.
Not all satellites are geostationary.
a.
Why are some weather satellites and surveillance satellites not geostationary?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
b.
These satellites usually have periods much less than 1 day. Where do they need to be placed
relative to geostationary satellites?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
5.
Calculate:
a.
the orbital speed of the Moon around the Earth:
_______________________________________________________________________________
_______________________________________________________________________________
b.
the orbital speed of the Earth around the Sun:
_______________________________________________________________________________
_______________________________________________________________________________
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Gravitation
Website References
The following is a list of recommended Internet sites relevant to the topic of Gravitation. Students and
teachers should note that many sites are from educational institutions in a variety of countries and the
curriculum contained therein may not be consistent with Australian physics curriculum. Also in some
cases an alternative system of units (eg. pounds, feet, seconds) is used.
•
http://www.sciencejoywagon.com/physicszone/_vti_bin/shtml.exe/default.htm
A page from a comprehensive site full of different situations, movies, simulation and text.
•
http://www.astro.queensu.ca/~musgrave/cforce/OrbitApplet.html
An applet showing the orbits of two masses at different orbital radii with graphs of potential
energy.
•
http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=24
has a java applet letting you set the speed and view the resulting orbit
•
http://astro.u-strasbg.fr/~koppen/apindex.html#SPACE
a collection of space and astrophysics applets.
•
http://www.glenbrook.k12.il.us/gbssci/phys/Class/circles/u6l3c.html
a useful theory page with worked examples
•
http://www.ticalc.org/pub/83plus/basic/science/
This Texas Instruments site has calculator programs to download and use.
•
http://www-spof.gsfc.nasa.gov/stargaze/Sgravity.htm
Theory site with lesson plan, links to other physics “lesons”.
•
http://en.wikipedia.org/wiki/Law_of_universal_gravitation
page from a free online encyclopedia
•
http://www.walter-fendt.de/ph14e/
collection of applets, Kepler’s 1st and 2nd Laws amongst them.
•
http://hyperphysics.phy-astr.gsu.edu/hbase/grav.html#grvcon
Gravity section of this comprehensive physics site.
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