Presentation on theme: "Rotation: circular motion around an inside axis - example the earth spinning on its own axis. Revolution: circular motion around an outside axis - example."— Presentation transcript:
1Rotation: circular motion around an inside axis - example the earth spinning on its own axis. Revolution: circular motion around an outside axis - example the earth moving around the sun.
2Circular motionWe have several ways to describe the speed at which an object turnsTangential speedLinear speedRotational speedAngular velocity
3Circular motionTangential velocity or VT which describes the speed at which an ant on the outside of the spinning turntable would be traveling at any instant relative to an outside observer. This is also known as linear velocity.This can also be thought of as the speed the ant would be going if he suddenly flew off of the rotating disk.
4Circular motionRotational velocity or (the greek lower case letter omega).This is a measure of how fast an object is moving with relation to its axis of rotation. This motion will be described by how many revolutions the object makes around it axis of rotation. We will measure it in Revolutions per minute or RPMs in this class.
5Linear speed or velocity = tangential speed or velocity = distance/time and is measured in “meter/second”The red arrow represents the linear velocityrotational speed or velocity orangular speed or velocity, (omega), = = number of rotationstimeand is measured in RPM’s or degrees or radianssecond secondMeasure the time it takes for the blue arrow to go around once, its period,T, and calculate its angular speed in rotations per second.
6On a spinning turn table which point has the fastest speed? Well, it really depends!Which has the greatest vT?Which has the greatest ?
7To calculate the linear velocity we could take distance/time Or the circumference/timev = 2πr/TIf the diameter of the circle is 4 m and the period is 3 seconds calculate the linear velocity.
8If something moves in curved path must there be a force on it? Use this to motivate circular motion involves acceleration.A ball is going around in a circle attached to a string. If the string breaks at the instant shown, which path will the ball follow?10
9Centripetal ForceA center-seeking force that causes an object to follow a circular path.
10Centripetal force Causes circular motion it is a real force “center seeking”Centripetal force
13G Force, 10 m/s/s or your weight 0 stationary or moving at a constant velocity0.4 "pedal to the metal" in a typical American car1.7 "pedal to the metal" in a Formula One race car2 Extreme Launch™ roller coaster at start3 space shuttle, maximum at takeoff**; jet fighter landing on aircraft carrier8 limit of sustained human tolerance25 R. F. Gray, centrifuge*, 5 s duration,40 USAF chimpanzee, centrifuge*, 60 s duration,35 - 40J. P. Stapp, rocket powered impact sled, 1 s duration,60 chest acceleration limit during car crash at 48 km/h with airbag70 - 100 crash that killed Diana, Princess of Wales,83 E. L. Beeding, rocket powered impact sled, 0.04 s duration,247 USAF chimpanzee, rocket powered impact sled, s duration,
14“center-fleeing”, away from center Centrifugal force“center-fleeing”, away from centerApparent outward force experienced by a rotating bodyFictitious force – it is not real but do to the effect of inertia
18The whiteboard was being carried along a straight line path; the ball rest on top of the whiteboard and followed the same straight-line path. Then suddenly, the board was turned leftward to begin a circular motion; yet the ball kept moving straight.
26A linebacker rides on the outside horse of a merry-go-round A linebacker rides on the outside horse of a merry-go-round. The merry-go-round’s diameter is 10 m it takes 5 seconds to complete 1 rotation. If the linebacker has a mass of 100 kg…Is he revolving or rotating?He is revolving…..The merry-go-round is rotating
27A linebacker rides on the outside horse of a merry-go-round A linebacker rides on the outside horse of a merry-go-round. The merry-go-round’s diameter is 10 m it takes 5 seconds to complete 1 rotation. If the linebacker has a mass of 100 kg…Calculate his linear velocity.
28A linebacker rides on the outside horse of a merry-go-round A linebacker rides on the outside horse of a merry-go-round. The merry-go-round’s diameter is 10 m it takes 5 seconds to complete 1 rotation. If the linebacker has a mass of 100 kg…Calculate his centripetal force .
29A linebacker rides on the outside horse of a merry-go-round A linebacker rides on the outside horse of a merry-go-round. The merry-go-round’s diameter is 10 m it takes 5 seconds to complete 1 rotation. If the linebacker has a mass of 100 kg…Calculate his centrifugal force.It’s not real, just like…..
30How does a train stay on the tracks? Believe it or not it is not the inner rim. The rail often does not touch it
31The wheels of the train are tapered The wheels of the train are tapered. A cylinder rolls straight, whereas a cone will roll in a circle.Why?
32Which part of the tapered wheel moves with a greater VT Which part of the tapered wheel moves with a greater VT? The part with the smaller radius A, or the larger radius B?Since B is moving faster it covers more distance and causes it turn.
33Let’s see what happens if we roll a cylinder wheel down a Curved track Will the wheel stay on the track?If the track starts turning right, underneath the train, (which has plenty of momentum), what will happen?There will be nothing to make the wheels turn rightIt does not correct itself as it slides off the trackIt is a train wreck
35Let’s see what happens if we roll a tapered wheel like the one shown down a track Will the wheel stay on the track, if the track starts turning left?The trains momentum tries to carry it straight forward.It does not correct itself, it wants to go right which is opposite of direction it needs to go!FasterSlower
37What happens if the track turns left The right wheel will move faster, with the same rotational speed but a larger VT, and the left wheel will move slower, so the train will roll to the left and self corrects. Staying on track.FasterSlowerSlowerFaster
38So if you want Thomas the Train to turn, you let its momentum do the work for you! If you want the train to turn left, you just make the tracks turn left and the rest happens by itself!! Horray for Thomas the Train!SlowerFaster
39Trains are really smart, and very useful. But some are Evil!
42What would happen if the rotation was faster? What would happen if you increased the radius of the space station?To feel 1 g force, if the space station is larger would it have to be spinning as fast?
43Does an astronaut have to apply a force to an apple keep it moving in a circle? Would the astronaut feel “weight” from the apple?What would happen if he lets go of it?Is there a net force on it when he lets it go?What direction does the apple go as seen by the astronaut?
44Inertia - resists acceleration, a property of matter, a kind of laziness of matter - depends on the massRotational Inertia “The moment of inertia” “I”, resists rotational acceleration, depends on the distribution of the mass, that is where the mass is located
45The further the mass is away from the axis of rotation, fulcrum, the greater the rotational inertia, that is the more lazy it to change its rotational motion.If these two rods have the same mass and CG but rod A has the mass located in the center and rod B has most of the mass located at the ends.Which is harder to rotate?Why?
46What happens when you put an equivalent force on each roll? Which one will rotate easier?Why?
47Which of these would have the least rotational inertia in their legs? Which would have the fastest gate?
48A solid hoop and a hollow cylinder roll down an incline. Which one will have the greatest rotational inertia?Why?Which one will be more sluggish?Which one will win the race?
49angular momentum (A.M.) is equal to - rotational velocity or - angular velocity,TIMES,I - rotational inertia or the moment of inertiaA.M. = I
50conservation of angular momentum the total angular momentum of a system does NOT change,unless an outside forceacts on it, therefore,angular momentum before = angular momentum after Ibefore = Iafter