Chap 3: Laws of Motion

1. Chap 3: Laws of Motion What is motion? what do scientists define as motion ? Why do the planets move the way they do? http://neo.jpl.nasa.gov/1950da/animations.html

2. Motion What is motion? what do scientists define as motion ? Why do the planets move the way they do? Keep in mind the way scientists like to work: Observe Define Hypothesize/Predict Test repeat

3. Note:the study of motion was motivated by the motion of celestial objects. Galileo … … studied motion; … was the first to use a telescope for astronomical observations; … saw that there were ojects that did not move around the Earth !

4. Galileo Galilei (1564-1642) “the astronomer” Believed in the Copernican model. Demonstrated that Kepler’s and Copernicus’ ideas were right by making observations with his telescope. • 1. The heavens are not “perfect”: • geological features on the moon • sunspots on the surface of the Sun 2.The moons of Jupiter obey Kepler’s laws 3.Phases of Venus, supporting heliocentric theory 4.Observed that Mars, Jupiter and Saturn had no phases. 5. Observed individual stars in the Milky Way, thereby showing stellar parallax measuring is possible.

5. Galileo Galilei (1564-1642) Believed in the Copernican model. Demonstrated that Kepler’s and Copernicus’ ideas were right by making observations with his telescope. • 1. The heavens are not “perfect”: • geological features on the moon • sunspots on the surface of the Sun

6. Galileo Galilei (1564-1642) 2.The moons of Jupiter obey Kepler’s laws

7. Galileo Galilei (1564-1642) 3.Phases of Venus, supporting heliocentric theory 4.Observed that Mars, Jupiter and Saturn had no phases.

8. geocentric heliocentric http://astro.unl.edu/classaction/animations/renaissance/ptolemaic.html 3.Phases of Venus, supporting heliocentric theory 4.Observed that Mars, Jupiter and Saturn had no phases.

9. Galileo Galilei (1564-1642) Believed in the Copernican model. Demonstrated that Kepler’s and Copernicus’ ideas were right by making observations with his telescope. 2.The moons of Jupiter obey Kepler’s laws 3.Phases of Venus, supporting heliocentric theory 4.Observed that Mars, Jupiter and Saturn had no phases. 5. Observed individual stars in the Milky Way, thereby showing stellar parallax measuring is possible.

10. Galileo Galilei (1564-1642) “the physicist” Galileo also experimented with falling and moving objects and crafted a theory of motion. Galileo’s workshop at the Deutches Museum in Munich, Germany

11. Galileo Galilei (1564-1642) “the physicist” Galileo also experimented with falling and moving objects and crafted a theory of motion. • 1. • An object in motion will continue moving along a straight line with a constant speed until an unbalanced force acts on it.

12. 2. dropped objects move down at 10 m/s /s WHY? t=3 s v=30 m/s

13. Gravity makes things accelerate at 10 m/s2 Iron ball Wood ball Acceleration of gravity is independent of the mass of the falling object!

14. Fourth manned lunar landing with David R. Scott, Alfred M. Worden, and James B. Irwin. Landed at Hadley rilleon July 30, 1971. www.hq.nasa.gov/alsj/a15/video15.html#closeout3

15. Observation Define __________ ? How do we describe motion?

16. How do we describe motion? (define it) 100 m/s displacement per time 10 m/s South-East … & direction 60 km/hr --> 30 km/hr --> 0 changing displacement per time

17. How do we describe motion? (define it) Speed: Rate at which object moves Velocity: Speed and direction Acceleration: Any change in speed or direction Thank you, Galileo

18. Motion: speed, velocity, & acceleration What about the mass?

19. Yes, motion depends on mass, too. Motion with Mass Momentum Linear Momentum = mass  velocity Angular momentum is rotational momentum of a spinning or orbiting object

20. So far….. Describing Motion: (basic ingredients) change in position (displacement) time mass direction speed velocity acceleration momentum

21. Isaac Newton (1642-1727) • Born the year Galileo died • Contemporary of Bach • Derived laws of gravity and other laws of physics “If I have seen further, it is by standing on the shoulders of giants.” --Isaac Newton

22. Isaac Newton (1642 - 1727) • Building on the results of Galileo and Kepler • Adding physics interpretations to the mathematical descriptions of astronomy by Copernicus, Galileo and Kepler Major achievements: • Invented Calculus as a necessary tool to solve mathematical problems related to motion • Formulated the three laws of motion • Formulated the universal law of mutual gravitation

23. Newton’s 3 Laws of Motion science.discovery.com/interactives/literacy/newton/newton.html 2 3 1 Inertia F = ma action = reaction

24. 1. Newton’s Laws of Motion Also known as : The Law of Inertia A body continues at rest or in uniform motion in a straight line unless acted upon by some net force.

25. Newton’s 1st: object will stay at rest (or in uniform motion) until acted on by a FORCE

26. 1. Newton’s Laws of Motion An astronaut floating in space will continue to float forever in a straight line unless some external force is accelerating him/her.

27. 2. Newton’s Laws of Motion The acceleration, a, of a body is directly proportional to the net force F, in the same direction as the net force F, inversely proportional to its mass, m. a = F F = m a m

28. Newton’s 2nd: F = ma (unbalanced forces cause changes in motion.)

29. 3. Newton’s Laws of Motion To every action, there is an equal and opposite reaction. M = 70 kg V = ? The same force that is accelerating the boy forward, is accelerating the skateboard backward. m = 1 kg v = 7 m/s

30. Newton’s 3rd: action - reaction

31. Newton’s 3rd: action - reaction

32. The Universal Law of Gravity Any two bodies are attracting each other through gravitation, with a force proportional to the product of their masses and inversely proportional to the square of their distance: Mm ^ F = - G d d2 (G is the Universal constant of gravity.)

33. What determines the strength of gravity? The Universal Law of Gravitation: • Every mass attracts every other mass. • Attraction is directly proportional to the product of their masses. • Attraction is inversely proportional to the square of the distance between their centers.

34. F = m a All objects on Earth fall with the same acceleration, g. g = 9.8 m/s2 (about 10 m/s2 --- Galileo) The acceleration: a = g Your weight is the force of Earth on YOU

35. Summary … so far: • How do we describe motion? • Speed = distance / time • Speed & direction => velocity • Change in velocity => acceleration • Mass effect motion • Momentum = mass x velocity • Force causes change in momentum, producing acceleration

36. Motion • described by: speed, velocity, and acceleration • determined by: Newton’s 3 Laws • has: energy • Energy • makes change

37. Energy makes matter move,too. Moving matter has energy. Energy and matter changes form. Energycannot be destroyed.

38. There are 2 forms of ENERGY Kinetic energy is motion–– of waves, electrons, atoms, molecules, substances, and objects. Potential energy is stored energy and the energy of position of objects, nucleus, chemical

39. There are 2 forms of ENERGY Kinetic energy is motion–– Electrical --- charges Radiant --- EM energy Thermal --- heat Motion --- Newton’s Laws Sound --- waves through substances

40. There are 2 forms of ENERGY Potential energy is stored energy and the energy of position Chemical --- stored in bonds (atom/molecule) Stored mechanical --- springs, rubber band Nuclear --- stored in nucleus (fusion/fission) Gravitational --- stored in position

42. Gravitational Potential Energy On Earth, GPE depends on: • object’s mass (m) • strength of gravity (g) • distance object could potentially fall

43. Gravitational Potential Energy In space, an object or gas cloud has more gravitational energy when it is spread out than when it contracts. • A contracting cloud converts gravitational potential energy to thermal energy.

44. Mass-Energy • Mass itself is a form of potential energy E = mc2 • A small amount of mass can release a great deal of energy • Concentrated energy can spontaneously turn into particles (for example, in particle accelerators)

45. Energy • Energy can be neither created nor destroyed. • It can change form or be exchanged between objects. • The total energy content of the Universe was determined in the Big Bang and remains the same today. Energy is Conserved

46. Conservation of energy (energybefore = energyafter ) Anything else conserved? Conservation of momentum

47. Conservation of Momentum BEFORE • The total momentum of interacting objects cannot change unless anexternal force acts on them • Interacting objects exchange momentum through equal and opposite forces AFTER

48. Conservation of angular momentum Angular momentum conservation also explains why objectsrotate faster as they shrink in radius

49. MASS, WEIGHT… does it matter? YES! MASS is the amount of matter of the object. Weight is the amount of force on the object.

50. Let’s apply EVERYTHING we know about motion to orbital motion