2. PHYSICS CH 2 C ONCEPTUAL P HYSICS V. HASSELL

3. 4-Jun-16 Physi cs 1 (Gar cia) SJSU A RISTOTLE & G ALILEO Aristotle was great philosopher but not such a good scientist. Aristotle’s theory of motion is wrong. Took 2000 years before Galileo got motion right.

4. A RISTOTLE ON M OTION (350 BC) Aristotle attempted to understand motion by classifying motion as either (a) natural motion forces acting at a distance (b) or violent motion contact forces

5. 4-Jun-16 Physi cs 1 (Gar cia) SJSU M OTION ACCORDING TO A RISTOTLE (II) Pushing or pulling an object causes “unnatural” motion (or “violent” motion). If cause is removed (stop pushing) then object returns to “natural” state and stops moving. BRICK Pushed brick slides but then comes to a stop

6. 4-Jun-16 Physi cs 1 (Gar cia) SJSU M OTION ACCORDING TO A RISTOTLE (I) Every object has a “natural” state. In “natural motion”, “Earth” elements (stone, apple, you, etc.) are drawn to the Earth. Heavier objects are more strongly attracted so they fall faster (stone falls faster than a feather). Aristotle Reality Important: These are Aristotle’s ideas, but he’s wrong!

7. 4-Jun-16 Physi cs 1 (Gar cia) SJSU N ATURAL & U NNATURAL M OTION Aristotle thought objects in unnatural motion would first stop, then fall. He was wrong! “Unnatural” “Natural” Reality

8. “Large object tend to 'strive harder'.” He stated that “The Earth remains at rest.”

10. Geocentric Model - Earth Centered Universe

11. C OPERNICUS (1500' S ) "The Earth and planets orbit the Sun.” He reasoned this from his astronomical observations.

12. G ALILEO - ONE OF 1 ST MODERN SCIENTIST Challenged beliefs- earth center of universe large masses fall faster Developed the scientific method

13. 4-Jun-16 Physi cs 1 (Gar cia) SJSU G ALILEO ’ S I NCLINES (I) Downhill: Speed increases Uphill: Speed decreases Flat surface: Speed increases, decreases, or constant? Questions existence of “natural Earth” state of not moving.

14. Friction - a force that resists motion e.g. air resistance and sliding on rough surfaces Inertia - the resistance of an object to change in its state of motion “Sluggishness” http://www.youtube.com/watch?v=w3Vhz9b6iKghttp://www.youtube.com/watch?v=w3Vhz9b6iKg Bow and Arrow Demo: Ball and incline plane

15. Galileo’s Incline Planes

16. 4-Jun-16 Physi cs 1 (Gar cia) SJSU G ALILEO & F ALLING Pull of gravity (weight) obviously larger for a bowling ball than for a baseball. YET the two balls fall with the same speed. What about a feather? (Answer in Chapter 4)

17. I SAAC N EWTON (1642-1727) a.k.a “Law of Inertia” A body remains at rest or moves in a straight line at a constant speed unless acted upon by a force. His three laws of motion first appeared in his book called Principia.

18. “If I have seen further it is by standing on the shoulders of giants”

20. N EWTON ’ S F IRST L AW E XAMPLES Weight and string Card, cup, and coin Fixing a Hammer Demo - Coins on elbow Demo - Lead Brick and Hammer Demo - Table setting http://www.youtube.com/watch?v=T9KPwNeCdSg Figure 2.4

21. 4-Jun-16 Physi cs 1 (Gar cia) SJSU N EWTON ’ S F IRST L AW OF M OTION An object at rest remains at rest & an object in motion remains in uniform motion*, unless a force acts on the object. * Moving in a straight line with constant speed.

22. 4-Jun-16 Physi cs 1 (Gar cia) SJSU N EWTON ’ S F IRST L AW OF M OTION Object at rest (not moving) No force on object Uniform motion Note: Object at rest is just uniform motion at zero speed. then

23. 4-Jun-16 Physi cs 1 (Gar cia) SJSU D EMO : R IDING L IGHT R AIL When a moving train stops, you continue moving forward. When the stopped train starts moving again, you remain stationary and are thrown backwards

24. 4-Jun-16 Physi cs 1 (Gar cia) SJSU D EMO : R OLLING, ROLLING, ROLLING WALL All moving together Bottom car stops. Other two continue With same speed.

25. 4-Jun-16 Physi cs 1 (Gar cia) SJSU D EMO : T ABLECLOTH P ULL Tablecloth Flower Vase Yank quickly

26. 4-Jun-16 Physi cs 1 (Gar cia) SJSU D EMO : R ING Y ANK Coin Ring Beaker Yank quickly

27. 4-Jun-16 Physi cs 1 (Gar cia) SJSU D EMO : I NERTIA B ALLS Heavy Cannon Balls Upper String Slo w pull Quic k yank Lower String Which string breaks in each case?

28. 4-Jun-16 Physi cs 1 (Gar cia) SJSU D EMO : P APER P ULL Quick yank What happens in each case? Which roll has more inertia?

29. 4-Jun-16 Physi cs 1 (Gar cia) SJSU N ET F ORCE same as The Newton is metric unit of force (about 1/5 pound). When several forces act on an object, the forces add together. Sum of forces called net force or total force BRICK 3 Newtons 5 Newtons 8 Newtons

30. 4-Jun-16 Physi cs 1 (Gar cia) SJSU C HECK Y OURSELF ?

31. Image from Isaac Newton's Principia (1687).

33. 10 N NET FORCE A force or a combination of forces produces changes in motion (accelerations). 10 N m = 20 N m 10 N m = 0 N m 10 N m 20 N = m

34. THE EQUILIBRIUM RULE Examples of Mechanical Equilibrium: Hanging from a tree Weighing yourself on a set of scales Computer setting on a table Car parked on an incline Normal up Weight down Scales pushing up Tree pulling up Normal Friction

35. 4-Jun-16 Physi cs 1 (Gar cia) SJSU E QUILIBRIUM R ULE same as If an object is at rest then the net force must be zero. Similarly if in uniform motion. BRICK 3 Newtons Zero Newtons (No Force) When this happens we say that forces “balance.”

36. 4-Jun-16 Physi cs 1 (Gar cia) SJSU D EMO : U P +U P =D OWN +D OWN STICK (2 Newtons) 10 Newton Iron mass Scale reads 5 Newtons Scale reads 7 Newtons The two upward forces (by people holding the scales) must always be equal to the two downward forces (weight of stick and iron mass). Stick is at rest. 5+7=10+2

37. 4-Jun-16 Physi cs 1 (Gar cia) SJSU S UPPORT F ORCE Solid surfaces exert a force, called a support force, on objects pressed against them. 100 Newton Gold Brick 100 Newton Support force Downward force (weight) balanced by upward force (support). How much is the net force on the brick?

38. The Equilibrium Rule

39. Scales pushing up Weight down SUPPORT FORCE A table can supply an upward support force also known as a normal force. When we say “normal to” we are saying “at right angles to”. Normal up Weight down

40. Equilibrium is a state of no change. If an object moves in a straight line with no change in speed, it is in equilibrium. EQUILIBRIUM OF MOVING THINGS Examples: Driving at constant velocity Force from road Air Resistance Normal up Weight down Terminal velocity in parachuting Weight down Air resistance

41. It is hard to detect the motion of the earth because we are moving with it. Early science could not predict large enough forces to move the earth. Can Hewitt’s bird drop down and catch the worm if the Earth moves at 30 km/s? Demo - Cart and ball launcher THE MOVING EARTH

42. W HICH PERSON BELOW IS MOST HIGHLY RECOGNIZED FOR PROPOSING A HELIOCENTRIC UNIVERSE ? (a) Aristotle (b) Newton (c) Galileo (d) Copernicus

43. If an object weighs 10 lb, what must the air resistance force be if the object is falling and has reached terminal velocity? (a) 10 lb (b) 32 lb (c) there is no way of telling without knowing what the value of the terminal velocity is

44. N EWTON ' S CONCEPT OF MOTION SAID THAT THE NATURAL STATE OF AN OBJECT WAS (a) constant velocity (b) constant acceleration (c) constant net force

45. D EMONSTRATIONS FOR C HAPTER 2 Ball and incline plane Weight and string Card, cup, and coin Swinging Rocks Coins on elbow Table setting Bottle, hoop, and chalk Cart and ball launcher Lead Brick and Hammer