Question

Physics 220 Activity 13.4 Challenge your wIL Challenge Problems C) The Struggle is wheel 1) Hold a bike wheel (non-spinning with its axis horizontal straight out in front of you at shoulder height. Arms straight and horizontal and elbows locked. QUICKLY push one end of the axio out a small amount and simultaneously pull the other end a little closer mine the direction of the you exerted to you, by moving your shoulders slightly. Draw a sketch of the bike wheel and deter- 2) Get the wheel rotating very quickly and repeat the procedure. Consider these questions: How does the ade "want to move? Let it move the way it wants to move". Do not resist it! How are the directions your hands are pushed by the wheel's axdes related to the initial directions you tried to move your hands? How did L want to change? Assuming you let it change the way it wanted to", what was AL? Explain this by starting with the horizontal forces you exert on the axde in determining the net angular impulse, AL = Teat. Showing the vectors L, AL and the net impulse, Tnetat, on a second sketch above. D) Precession: It wheelly doesn't fall 1) Get the bike wheel (or gyroscope) spinning as fast as you can. Then, while one person holds the wheel horizontally by the "handles', another person should securely hold the rope loop in a vertical position. Next, the person holding the handles lets go completely. Observe what happens when only the rope is supporting the spinning wheel. 2) Now, determine the torque caused by the Earth's pull acting at the center of gravity, by us- ing the point where the rope is attached as the point of rotation. Draw a sketch of the wheel vectors representing L, AL, L, and Tnet. Show how this torque causes the wheel to precess (the change in rotational direction you see) rather than simply fall down.

Answer 1

F 1 IF T=řx The torque will act vertically upward.

C 2)The hands are pushed vertically upwards due to the torque.The L changes in such a way that the total angular momentum of the system is conserved.∆L is T∆t (angular impulse).When we apply force this causes torque in the vertically upward direction which changes L to L+∆L.

Direction of rotation سجل LAL AL (parallel to a

D 1)The wheel starts precessing .

D 2)

The spin angular momentum is along the rotation axis as shown, but the toque about the support point is in a direction perpendicular to the angular momentum. The torque produces a change in which is perpendicular to L. Such a change causes a change in direction of Las shown but not a change in its size. This circular motion is called precession Wheel and axle supported at one end by cord Axis about which the gravity torque would tend to rotate the system Direction of torque due to weight of wheel L = 16 mg Temgl L New angular momentum after time 1 Torque due to weight causes precession in the direction of AL AL If the wheel is not spinning, the apparatus just rotates downward toward a vertical orientation f you curl the fingers of your right hand in the direction of that expected rotation, then your humb will point perpendicular to the spin axis in the direction of the torque produced by gravity. The tip of the angular momentum vector, and therefore the axle of the wheel, will recess in that direction