Use Mario toy and ball on string for demo Use Mario toy and ball on string for demo. Also use bucket of water in the example problem! Determine 4 equations as specified by the lab manual for experiment 10.

Class Notes 17 October Turn in HW / Pick up HW Today: Do NOT “back rotate” FBDs Use SFx=max and SFy=0, show FN #1: There are 3 force; no Fslide. #1: Hiding neg sign #5:Not Graded #4b: Moves accelerates downward Today: Centripetal Force!

Can this thread lift up a 500-gram mass? Yes No Can we have another week off? Answer is both A or B! Gently lifting FT = mg, but if I quickly lift FT = mg + ma. 2016: Vote was 13, 0, 2

Useful Terms A complete cycle takes a certain amount of time, called the period, T So v = 2pr/T (speed = dist/time) The number of cycles in a standard time is called the frequency, f. f  1/T, [f] = s–1 = Hz (Hertz)

A particle moves in uniform circular motion. Is its velocity constant A particle moves in uniform circular motion. Is its velocity constant? Is its acceleration constant? Yes / Yes Yes / No No / Yes No / No Answer is D. The direction of both the velocity and acceleration is changing. 2016 Vote: 3, 4, 3, 5

CALLED the centripetal force. While moving in a circle, the net force inward on an object is called the centripetal force. This is not a special new force, just a matter of Newton’s 2nd law. CALLED the centripetal force. NEVER EVER EVER will you have a force on your FBD called FC. SF = Fnet = maR

Examples What is the tension in a string as a small 30.0 gram mass is swung in a horizontal circle (r = 50.0cm), at a rate of 3.00 revolutions per second? Ignore the effects of gravity. Do this with ball on string. Realize that 3 revs per second implies T = 0.333 s. FT = 5.33 N (FT = mv2/r)

If I swing a ball in a vertical circle at a constant speed, where is the tension the greatest? Top Bottom Sides It is the same everywhere More information is needed to determine the correct answer. Answer is B. At the bottom the tension supports the weight and provides the centripetal force. 2016 Vote: 3, 6, 4, 2, 0

Examples How fast must I rotate a bucket to keep it from spilling? Take the length of my arm to be 90.0 cm. Spin water in bucket in a circle, with a student lying underneath it! 31.5 rpm, T=1.90s

Examples How fast may a car travel when negotiating a turn if the radius of curvature is 150. ft and s=0.600? Use N2 to find v = 36.7 mph If no friction is present, what must be done? Explain why static not kinetic.

Is it possible for a moving car to go around a curve if no friction? Yes No Can’t turn on ice. I think all surfaces should be frictionless – then I wouldn’t have to do the derivations for exp 10 Answer is B, so long as we bank the turn. 2016 Vote: 12, 1, 0, 2

Examples How fast may a car travel when negotiating a turn if the radius of curvature is 150. ft and s=0.600? Use N2 to find v = 36.7 mph If no friction is present, what must be done? Bank the turn at an angle of

Homework For lab Read Chap 5, sec 1-5 Do problems on worksheet: Yes, a FBD is required for each Yes, you must turn these in to me. For lab Derive 4 equations required for experiment 10.