1. What do we know about gravity?

2. What is gravity? What is the force of gravity? What are the effects of gravity? What do we know about gravity? How can we make use of gravity?

3. Mapping the gravitational field © ESA

5. GOCE had an orbital height of only 254.9 km. What difficulty might this cause? © ESA

6. GOCE experienced air resistance or drag. It therefore required a propulsion system to counteract the effects of drag. © ESA

7. What was GOCE’s mission? Was it worth funding? © ESA

8. Pair and share What was GOCE and why was it such an important satellite? http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE GOCE Satellite Views Earth’s Gravity in High Definition http://news.bbc.co.uk/1/hi/8767763.stm GOCE Facts and figures: http://www.esa.int/SPECIALS/GOCE/SEMDU2VHJCF_0.html http://www.esa.int/SPECIALS/GOCE/SEMDU2VHJCF_0.html

9. The 'standard' acceleration due to gravity at the Earth's surface is 9.8 m s –2. In reality the figure varies from 9.788 m s –2 (minimum) at the equator to 9.838 m s –2 (maximum) at the poles.

10. GOCE measured this using sensitive gradiometers built using six accelerometers. The resolution was 1 cm in 100 km. That means that for every 100 km measured, the measurement will be accurate to within 1 cm. That’s accurate to 1 in 1,000,000.

11. How does this compare to the sensitivity and experimental uncertainties in our gravitational field strength measurement?

12. Earth’s natural satellite Greek philosophers understood that the moon is a sphere in orbit around the Earth. © ESA

13. Earth’s natural satellite They also realised that the moon reflected sunlight. © ESA

14. Earth’s natural satellite About 1850 years ago, Ptolemy (90–168) hypothesised that the moon and the Sun orbited the Earth. What evidence was there to support this view? © ESA

15. It was not until almost 1300 years later that this view changed, with the work of Copernicus (1473–1543). © ESA

16. Kepler (1571–1630) developed three laws which predicted that the orbits of the planets are elliptical, with the Sun at the focus. What evidence is there to support this? © ESA

17. Why does the moon remain in orbit around the Earth? © ESA

18. Because of the force of gravity – the weakest of the four fundamental forces and yet it keeps the universe in shape! © ESA

19. Newton (1642–1747) developed the theory of universal gravitation. This was a very important piece of work – not least because he proposed it to be 'universal‘, ie all parts of the universe obey the same laws of nature. © ESA

20. Newton’s theory proposed that the moon stays in place as a result of the same force that causes an apple to fall from a tree. © ESA

21. What evidence do we now have to support this theory? © ESA

22. Newton’s theory also proposed that each body with mass will exert a force on each other body with mass. It said that the force of gravitational attraction is dependent on the masses of both objects and inversely proportional to the square of the distance that separates them. © ESA

23. But Newton remained uncertain. He was not convinced that there could be action at such a distance without some medium, i.e. he was concerned about the distances over which this force acts and the fact that space is a vacuum. © ESA

24. How would this theory be written mathematically? © ESA

25. Credits: ESA where: F is force in newtons (N) m 1 and m 2 are the two masses measured in kilograms (kg) r is the distance between them (m).

26. Credits: ESA G is the universal constant of gravitation

27. Credits: ESA Determine the units of the universal constant.

28. Credits: ESA

29. The units of the gravitational constant are N m 2 kg –2. However, in the Higher Physics physical quantities data sheet the units are expressed as m 3 kg -1 s -2.

30. Credits: ESA The value of the gravitational constant was determined by Cavendish (1731– 1810) in the late 1700s. It was another hundred years before Boys (1855–1944) improved on its accuracy.

31. Credits: ESA G = 6.67428 × 10 –11 m 3 kg –1 s -2 as determined in 1895 by Boys. G remains one of the most difficult constant to measure with accuracy. In 2007 a further value was published which suggested an improvement on the accuracy.

32. Credits: ESA G = 6.67 × 10 –11 m 3 kg –1 s -2 is the value that we use for calculations in Higher Physics.

33. If Newton’s theory is correct, why don’t we notice the effects in everyday life? © NASA

34. If Newton’s theory is correct, why don’t we notice the effects in everyday life?

35. If Newton’s theory is correct, why don’t we notice the effects in everyday life?

36. If Newton’s theory is correct, why don’t we notice the effects in everyday life? What assumptions are made in this calculation?

37. Credits: ESA How does this formula link to the formula we have used connecting weight, mass and gravitational field strength?

38. Credits: ESA How does gravitational force vary with distance?

39. Credits: ESA The gravitational force is always attractive. Is this true of electrostatic and magnetic forces?

40. How does the gravitational force affect objects on an atomic scale?

41. Newton’s theory suggests that gravitational force acts over enormous distance. It is suggested that it is the reason that the moon remains in orbit around the Earth but what about the effect of the moon on the Earth?

42. Credits: ESA How does this formula link to the formula we have used connecting weight, mass and gravitational field strength?

43. A short challenge: a simple model Your challenge is to develop a simple model to demonstrate to P7/S1 students the importance of gravity in our solar system. You must: use resources typically found in an ordinary science laboratory be able to explain what your model demonstrates

44. Gravity assist and slingshot The theory of universal gravitation can be used in space travel. © ESA

45. One of the most famous lines in history… Watch the extracts from Apollo 13 © ESA

46. The principles of the gravity assist method? The advantages of it? © ESA

47. We have explored the effects of the force of gravity on a small scale, its importance in satellite motion and its use in space flight. We have discussed some of the historical story associated with our understanding of gravitational force, but we have yet to discuss a very significant impact of the gravitational force.

48. What do you know about the solar system? What do you know about its formation? © NASA

49. Within your home group create a mind map of your knowledge and understanding of the solar system and its formation.

50. Expert groups Using identified web resources, you will each work within an expert group to research one area associated with the formation of the solar system. You will return to your home group and teach others about your learning.

51. Expert groups The purpose of the task is to: understand the development of theories relating to the formation of the solar system, and the evidence to support or refute the theories consider the evidence for the role of gravitational force in the formation of the solar system.

52. University of Texas McDonald Observatory website, StarDate Online. http://stardate.org/astro-guide Group Hubble: The Inner Planets & Exploring our own Backyard Group Newton: The Outer Planets & the Realm of the Giants Group Herschel: Minor Bodies & Remnants from the Beginning Group Kepler: The Sun & The Solar System: Home Sweet Home

53. © NASA Return to your home group and explain your expert learning to your group. As you go along, adapt your mind map. Add new information and delete any information you now know to be incorrect.

54. http://www.nasa.gov/images/content/16 2284main_image_feature_693_ys_full.j pg © NASA Examine this image from the Spitzer and Hubble telescopes. What information can we get from this image, and others like it?

55. http://www.nasa.gov/images/content/16 2284main_image_feature_693_ys_full.j pg Amend your mind map to include this new information. © NASA

56. Where did the moon come from? Something more to consider: http://www.nhm.ac.uk/nature-online/space/planets-solar- system/moon/origins/index.html

57. © NASA Further sources of information: Cloud collapse simulations (face on and edge on) http://www.ifa.hawaii.edu/~barne s/ast110_06/quizzes/disc06.html

58. © NASA Further sources of information: http://earthobservatory.nasa.gov /Features/OrbitsHistory/ http://www.bbc.co.uk/programm es/p006t1ks Watch BBC Wonders of the Solar System Episode 1 Empire of the Sun and Episode 2 Wonder out of Chaos

59. © NASA Communicating science! What would be the most appropriate way to summarise on an individual basis your understanding of the hypotheses on the formation of the solar system and the scientific evidence to support these hypotheses?

60. The birth (and death?) of our Sun © ESA

61. © NASA This image shows a planetary nebula. A sun-like star has undergone 'death tremors' at the end of its life. The star had difficulty in getting enough fuel to keep up its nuclear furnace, and has now shed off some of its surface material in two directions.

62. Have we answered any or all of these questions? What is gravity? What is the force of gravity? What are the effects of gravity? What do we know about gravity? How can we make use of gravity?

63. Unanswered… Gravity as a property of space–time. The graviton as the exchange particle of gravitational fields. The nature of mass. Black holes (and white holes?)

64. What is the universe made of? Why does the gravitational mass of the galaxy exceed the mass of the known matter? Is there something else there? Or do we not really understand gravity at all? When were the first stars formed? What were they like? Do gravitational waves exist?*

65. Why do the four fundamental forces have the strengths they have? Is there a single unifying theory which links gravitational force to the other much better understood forces?

66. There is nothing new to be discovered in physics now. All that remains is more and more precise measurement. (Lord Kelvin, 1900) Address to the British Association for the Advancement of Science, 1900 ©Hunterian Museum and Art Gallery, University of Glasgow. Licensor www.scran.ac.uk.

67. ' When asked if he leaned toward the acceptance of any particular theory of gravitation: 'No, no, no, I accept neither theory, I accept no theory of gravitation. Present science has no right to attempt to explain gravitation. We know nothing about it. We simply know nothing about it.' Quoted in Invisible Light (1900) by George Woodward Warder ©Hunterian Museum and Art Gallery, University of Glasgow. Licensor www.scran.ac.uk.

68. 'This time next year,—this time ten years,—this time one hundred years,—probably it will be just as easy as we think it is to understand that glass of water, which now seems so plain and simple. I cannot doubt but that these things, which now seem to us so mysterious, will be no mysteries at all; that the scales will fall from our eyes; that we shall learn to look on things in a different way—when that which is now a difficulty will be the only commonsense and intelligible way of looking at the subject.' Presidential Address to the Institution of Electrical Engineers', 1889 ©Hunterian Museum and Art Gallery, University of Glasgow. Licensor www.scran.ac.uk.

69. So back to the ‘unanswered questions’ Do gravitational waves exist? In February 2016 scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced to the world that they had detected gravitational waves.

70. Scientists had detected the gravitational waves produced in a fraction of a second as a pair of black holes merged together The event took place 1.3 billion years ago and approximately 3 times the mass of the sun was converted into gravitational waves.

71. This animation shows how the gravitational waves were produced https://www.ligo. caltech.edu/vide o/ligo20160211v 10

72. Scientists reveal the ‘chirp’ detected at each of the LIGO facilities https://youtu.be/ egfBaUdnAyQ https://youtu.be/ egfBaUdnAyQ