2 11.1 Torque Torque produces rotation. NOT a force List times when you make an object turn or rotateNOT a forceTo make an object move you apply a force, force causes accelerationTorque is produced when a force is applied with leverageThe longer the handle the more leverage can be applied
3 11.1 continuedLever arm-the distance from the turning axis to the point of contactTorque = FdW=Fdd in torque is ┴ to the forced in work is parallel to the forceUnits= newton-meter
4 11.2 Balanced TorquesUse a triple beam balance to weight different massesWhat relationships do you notice?Torque in 2 different directionsCounter clockwise torque opposes clockwise torqueIf the two are equal the scale will be balancedF1d1=F2d2
5 11.2 Balance Torque Cont. 200N 2 m 2 m τ= 400 N-m τ= 400 N-m 200N 2 m
6 11.3 Torque and Center of Gravity Why can’t a person stand against the wall and then bend forward without falling forward?Your feet are not beneath your center of gravityThis creates torqueτ= FdHow could the torque be balanced so that a person standing against the wall doesn’t fall over?answerWhy do pregnant women get back pain?
7 11.3When a football is kicked or throw why does is rotate end over end instead of spiral?If a force is applied off center then torque is created thus causing the ball to move end over endHow do you get it to spiral?answer
8 11.4 Rotational Inertia What is inertia? Rotational inertia- the resistance of an object to changes in its rotational motionAn object rotating wants to keep rotating, an object that is not rotating wants to continue to not rotateTorque is required to change the rotational state of motionRotational inertia depends on massAnd the distribution of massThe greater the distance between the axis and the mass the greater the rotational inertia
9 11.4 Think about a baseball bat Why do some people use a shorter bat than other people?What does it mean to “choke up”?Why would a baseball player need to “choke up”?Compare the legs of a giraffe with that of a mouseList some differenceHow does rotational inertia apply?
10 11.4 Formulas for rotational inertia: pg. 157 If both cylinders were rolling down a ramp which would have more acceleration? (same mass, same radius)
11 11.5 Rotational Inertia & Gymnasics Human body has 3 axes of rotationMedian (z)Transverse (x)Longitudinal (y)All at 90° angle to one anotherRotational inertia is least about the longitudinal axis thus it is the easiest rotation to performTo increase longitudinal inertia extend an arm or a leg while spinningA summersault rotates about the transverse axisLeast when in tuck positionGreatest when fully extendedA cartwheel rotates about the median axis
12 11.6 Angular Momentum Angular momentum- inertia of rotation Vector quantityHas direction and magnitudeRotational velocity- when a direction is assigned a speedAngular momentum= rotational inertia x rotational velocityAngular momentum = I x ω
13 11.6 An external net torque is required to change angular momentum A moving bicycle is easier to balance on because the wheels have angular momentum there fore more torque is required.
14 11.7 conservation of angular momentum Law of conservation of angular momentum- if no unbalanced external torque acts on a rotating system, the angular momentum of that system is constantWith no external torque, the product of rotational inertia and rotational velocity at one time will be the same as at any other timeInitial conditionsWhat happens to V as you increase the velocity bar but keep the radius the same?What happens to V as you increase the radius but keep the velocity the same?What happens to the snowman as you change the radius under run time controls?