How Do Objects Move?

1. Great Idea #2: Newton’s universal laws of motion and gravity predict the behavior of objects on Earth and in space.

2. How Do Objects Move? Key Idea: One set of laws describes motions on Earth and in space • Universal laws of motion • The universal law of gravity Key Terms: • Force • Uniform Motion • Acceleration • Weight vs. Mass

3. Newgrange, Ireland:5,000-year old “passage tomb”

5. Stonehenge • On the Salisbury Plain of southern England • 4500 years old • Exact history is uncertain • Stonehenge Decoded by Richard Hawking

8. John Snow (1813-1858) He used the scientific method to discover that contaminated water at the Broad Street Pump was the source of a deadly cholera outbreak in London. His research saved countless thousands of lives.

9. The Idealized Scientific Method

10. Measurements and Observations • How would you measure a star’s position? • Compass – direction to an object (degrees from North) • Protractor w/ straw (degrees from horizon) • Plot changes from night to night • Planets (Mars) display retrograde motion • Patterns emerge

12. Ptolomy’s Model of the Solar System • Model of the universe with Earth at the center • Epicycle (wheels within wheels) • Why is it important? • Navigation • Astrology • Lasted 1500 years

13. Dead White Males • Nicolas Copernicus (1473-1543) • Sun-centered solar system • Tycho Brahe (1546-1601) • Meticulous measurements of planet positions • Johannes Kepler (1571-1630) • Mathematical analysis of planetary orbits • Galileo Galilei (1564-1642) • Founder of experimental physics

14. Ptolomeic vs. Copernican models • Earth- vs. Sun-centered • Perfect circles (still need epicycles) Ptolomy Copernicus

16. Tycho Brahe (1546-1601) • Observed a new star • Showed heavens can change over time • Designed and used new astronomical instruments • Collected data on planetary movements

17. The Quadrant

18. Tycho Brahe (1546-1601)

20. Johannes Kepler (1571-1630) • Mathematician • Assistant to Tycho Brahe • Inherited his notebooks • Traditional ideas of the solar system are wrong (Kepler’s Laws)

21. Kepler’s Laws of Planetary Motions First Law: Planets have elliptical orbits

22. Elliptical orbits

23. Kepler’s Laws Second Law: Orbits sweep out equal areas in equal times

24. Kepler’s Laws Third Law: Distant orbits take longer. (Average orbital radius)3 = k (orbital period)2 R3/P2 = constant

26. Galileo Galilei (1564-1642) • Mathematician • Improved the telescope • Observational astronomy • Founder of experimental science • Musical training • Arrogant and contemptuous of others • Published in Italian (vernacular) promoting Copernican view • Heretic (threatened with torture) so he recanted

28. Galileo – The Founder ofExperimental Science Galileo studied the relationship among distance, time, velocity and acceleration He observed that objects accelerate while falling:

29. Galileo’s Discoveries • Constant acceleration • Balls on a plane: v = at • Freefall • Constant acceleration at g • g = 9.8 m/s2 = 32 feet/s2 • Distance traveled (d) = ½at2

30. Speed, Velocity, and Acceleration • Speed = distance traveled over time • Velocity = speed with direction • Equation for speed: • Acceleration = rate of change of velocity • Equation for velocity:

31. Galileo’s Laws of Motion • Trajectories are parabolas • All objects fall at the same velocity • Distance of fall = k(Time)2 Remember Kepler (1571-1630) • Orbits are ellipses • Equal areas in equal times • (Radius)3 = k(Time)2 Now on to Sir Issac Newton (1642-1727)

32. Sir Issac Newton (1642-1727) • Born prematurely • Abandoned by his mother • Forced to run family farm • Sent to Cambridge University • Made fundamental advances in several scientific fields

33. Issac Newton’s – Plague Years (1665-1666) • Calculus 2. Laws of optics • Broke white light into colored light 3. Universal laws of motion 4. Universal law of gravitation

35. Two Types of Motions Uniform motion: No change in velocity or direction Acceleration: Change in velocity and/or direction

36. Issac Newton’s Laws of Motion 1st Law: Nothing happens without a force “A moving object will continue moving in a straight line at a constant speed, and a stationary object will remain at rest, unless acted on by an unbalanced force.” This law defines “force”

37. Issac Newton’s Laws of Motion 1st Law: Nothing happens without a force 2nd Law: Force = mass X acceleration (F=ma) “The acceleration produced on a body by a force is proportional to the magnitude of the force and inversely proportional to the mass of the object.” This law defines “mass”

38. Issac Newton’s Laws of Motion 1st Law: Nothing happens without a force 2nd Law: Force = mass X acceleration (F=ma) 3rd Law: Forces always act in pairs “For every action there is an equal and opposite reaction.”

39. Gravity (a universal force)

40. The Universal Force of Gravity Between any two masses there exists a force that is proportional to the masses and inversely proportional to the square of the distance between them. F = Gm1m2/d2

41. The Force of GravityF = Gm1m2/d2 Why mass x mass? Think of “rays of mass” radiating in all directions gravitational force = # of rays intersecting m1 m2

42. The Force of GravityF = Gm1m2/d2 Why inverse square of distance? Think about a flashlight: light intensity is greater at shorter distances Now double the distance: (4X the area = 1/4 the light)

43. The Force of GravityF = Gm1m2/d2 What is G? • G = universal constant of direct proportionality • Henry Cavendish • G = 6.67 x 10-11m3/s2-kg or • 6.67 x 10-11N-m2/kg2

44. Weight and Gravity • Weight = Gravity acting on an object’s mass • Weight depends on gravity Different on Earth vs. Moon • Mass is constant

45. Natural Laws Raise DeepPhilosophical Questions • What about free will? • Natural laws in other domains Economies (Adam Smith) Law (cause and effect) Politics (George Mason)