Video Education America Bringing Learning to Life Program Support Notes Grades 10 - College Gravitation 32mins 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 To order or inquire please contact VEA: America Phone: 1 866 727 0840 Facsimile: 1 866 727 0839 E-mail vea@veavideo.com Website www.veavideo.com WARNING This program is protected by copyright laws worldwide. Unauthorized copying, in whole or part, in any format, can result in substantial penalties for both individuals and institutions These notes can be freely copied for classroom use only.
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= Gm 1 m 2 /r 2 should of course be g = Gm/r 2. 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 Start of Program 00:00:22 Fundamental Forces 00:03:18 Summary 00:03:50 Newton s Law of Universal Gravitation 00:10:00 Summary 00:10:57 In Orbit 1 00:15:44 Summary 00:16:29 In Orbit 2 00:21:07 Summary 00:21:33 Gravitational Field Strength and the Inverse Square Law 00:27:47 Summary 00:28:40 Conclusion 00:28:51 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
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?
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 4. What is the formula for the force of attraction connecting the two masses m 1 and m 2 together? F = 5. Explain what you understand by the meaning of an inverse square law. r m 1 m 2 6. Why is the force of attraction between the Earth and ourselves so huge compared to the attraction between two apples?
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 M Moon = 6.427 10 23 kg R Moon = 3.41 10 6 m F = Gmm r Κ Κ Κ Κ Κ Κ Κ Κ Κ Κ Κ Κ = m 2 m 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. F centripetal = 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.
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. The period equation for a satellite is : T = 2 4π R GM E 3 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 m 2 / kg 2 M Earth = 5.98 10 24 kg R Earth = 6.38 10 6 m T = 28 days R 3 m GM T 4π E = 2 2 = R m =
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 g Earth? (include units!) 23. For the following table of values plot the graph of orbit radius (R) against gravitational field Strength R (m) 1 2 3 14 5 10 g-field g ¼ g 1 / 9 g 1 / 16 g 1 / 25 g 1 / 100 g gravitational field strength (g) 1.00 0.80 0.60 0.40 0.20 0.00 0 2 4 6 8 10 orbital radius (m)
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? v escape = 2GM R G = 6.67 10-11 N m 2 / kg 2 M Jupiter = 1.9 10 27 kg R Jupiter = 7.1 10 7 m v escape = m/s 26. Why is the theoretical gravitational field strength zero at the centre of the Earth?
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:
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 1 st and 2 nd Laws amongst them. http://hyperphysics.phy-astr.gsu.edu/hbase/grav.html#grvcon Gravity section of this comprehensive physics site.