Isaac Newton (1642-1727)

2. Galileo Galilei (1564-1642) Isaac Newton (1642-1727) Albert Einstein (1879-1955)

3. How Things Work The Physics of Everyday Life 3rd EditionBy Louis A. Bloomfield (ISBN 0-471-46886-X) John Wiley & Sons, Inc. The working of familiar objects and apparatus will illuminate a number of fundamental principles in Physics.

4. * * Purchase PRS clicker at the University Bookstore 2 1 4 4 The old Infrared clickers will no longer work with the university’s newly installed PRS system. 1 Power on your Clicker. 2 Press to stop autoscan. 3 Press again to display Setup Menu. 4 Scroll  or  for the ID menu.   Press to select it.  5 Input Student ID. Use  to backspace. Press to save your student ID. 

5. We’ll discuss the concept of FORCE as a demonstration of the importance of both precise DEFINITIONS and careful OBSERVATIONS in science. and study falling objects as an example of a scientific investigation a combination of Experience Observation Intuition Logic to frame the basic description using common sense to apply these ideas to new situations…draw conclusions …make predictions

8. Imagine set down at rest: a glass on the counter a ball on the billiards table a book on a desk if left undisturbed would remain at rest! No poking, prodding, pushing, or pulling

9. Just as obviously, common experience shows us that we move objects by force.

10. An object subject to NO external forces will A. be at rest. B. eventually come to rest. C. move at constant speed. D. move with increasing speed.

11. We tend to take the force of friction for granted It is an external force and in its absense it is natural to COAST! When released and no longer in contact with the bowstring (and propelled by its tension) the arrow does not stop!

12. An object subject to NO external forces will A.be at rest. B.eventually come to rest. C.move at constant speed. D.move with increasing speed. An object subject to a constant net external force will A.resist moving and remain at rest. B.move but eventually come to rest. C.move at constant speed as long as the force continues to be applied. D.move with increasing speed.

13. In an evenly matched arm-wrestling bout or tug of war match enormous forces may be involved, but little motion!

14. The tension and weight are exactly equal and opposite! Tension in supporting cable T T= -W They balance! Weight, the force due to gravity W T+W = 0 In this case there is no NET force!

15. Newton’s 1st Law “The Law of Inertia” An object at rest tends to remain at rest and an object in motion tends to remain in motion with the same speed and in the same direction unless acted upon by an unbalanced force. constant velocity of ? constant velocity In the absence of a net force, a object’s velocity remains constant!

16. A hockey puck slides across the ice at constant velocity. The total force acting on the puck must be A) zero B) greater than zero Since the puck moves with constant velocity, the net force on the puck must be zero. This is just Newton’s First Law! You set your book on the bus seat next to you. When the bus stops suddenly, the book slides forward off the seat. Why? A) a net force acted on it B) no net force acted on it The action of the brakes acted to stop the bus itself. Nothing other than the tiny friction with the plastic seat upholstery acted to slow or stop the book.

17. A brief push starts this kid off from rest. An unbalanced force changes his tangential speed from 0 to v. introducing the mathematical convention of “delta” representing a small change.

18. If each time he swings past you give about the same PUSH you will boost his speed by an additional v. His speed will grow and grow with each successive push. What if you keep up by racing alongside and continue to push? Isn’t that like a bunch of successive pushes following uninterrupted?

19. Easy to push Hard to push To produce the same amount of acceleration, need to push the car much harder! How much? Twice as much mass requires twice the force! ? 100 as much mass requires 100 the force! F m

20. If a lot of others join in, each contributing an additional force, the net force will be greater, and the acceleration greater. Fa F m together with can be combined consistently to give Newton’s 2nd Law F = ma

21. Unveiled at last spring’s International Auto Show in Detroit: The Toyota FT-HS is a 400-horsepower hybrid sports car  its 3.5-liter V6 engine provide an acceleration of 0-to-60-miles-an-hour in 4 seconds v t acceleration, a = miles/hour sec +60 miles/hour = 15 4 seconds

22. X Y If X =Y then = ? A. 0 C. 1 E. XY B. ½ D. 2 F. infinity If 1 mile =5280 ft then = ? 1 mile 5380 ft

23. miles/hour sec +60 miles/hour = 15 4 seconds Notice60 miles/houris the same as miles hour 5280 feet 1 mile feet hour 60  = 316800 feet hour 1 hour 3600 seconds feet sec 316800  = 88 So alternately feet/sec sec +60 miles/hour = 22 4 seconds or 22 ft/sec2

24. More generally, if an object is already in motion before it starts accelerating: present velocity = initial velocity + at starting velocity at time=0 A car traveling 35 mi/hr accelerates 4 over the next 5 seconds. What final speed does it attain? mi/hr sec mi/hr sec v = 35 mi/hr + (4 ) 5sec = 35 mi/hr + 20 mi/hr = 55 mi/hr

25. The Space Shuttle touches down with a landing speed of ~100 m/sec (224 mi/hour), and comes to rest at the end of its runway within 40 seconds. What average acceleration does it undergo? starting velocity at time=0 -2.5m/sec2

26. 14 lb. medicine ball Tennis ball 2 ounces (57 grams) Softball 6.5-7.0 oz. 112 times heavier than a tennis ball! 32 times heavier than a softball! If all 3 balls were released simultaneously, from the same height, they would reach ground A. tennis ball first, medicine ball last. B. medicine ball first, tennis ball last. C. together at about the same time.

27. A large boat whose maximum speed in still water is v1, tows a smaller boat whose maximum speed is the smaller v2. across the lake. If both outboard motors run together at full bore, the speed that they travel together with will be A. the smaller value v1. B. the larger value v2. C. somewhere between v1 and v2.

28. Some answers: An object subject to NO external forces will C. move at constant speed. Notice that being at rest is just a special case of constant velocity (= zero). An object’s inertia will keep it from spontaneously changing its velocity: whether that’s starting to move from rest, or slowing down from a non-zero speed. It takes force to start something moving, but also to slow or stop it once its moving! An object subject to a constant net external force will D. move with increasing speed. If any unbalanced force can start an object moving…then a continuously applied force can only make it move faster and faster. People are confused when friction is high enough that an object slows to rest shortly after they stop pushing. In that case, the unbalanced force (friction alone) slows it to a stop. Pushing hard enough to just make up for (match) friction means all the forces have been balanced, and then there is no net (or unbalanced) force left over to speed the object up or slow it down. Any push beyond the amount needed to overcome friction will cause the object to accelerate. The net force would be your push minus the pull of friction.