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Lecture 8

PHY 2020 Lecture 8: Chapter 8-9

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PHY 2020

Exam 1 Review Chapter 8- Rotational Motion - Your pet “hamster” sits on a record player whose angular speed is constant. If the moves to a point twice as far from the center, then his linear speed is o Doubled - Tangential speed~ radial distance * rotational speed * rotational speed o v~rw - Motion of inertia o It is not just the mass that matters, but where the mass is located (with respect to rotational axis) - Explain why a long pole is more beneficial to a tightrope walker if the pole droops. o The tendency of the pole to resist rotation aids the acrobat. - A solid cylinder rolls down an incline faster than a hoop, whether or not they have the same mass or outer diameter. A hoop has greater rotational inertia relative to its mass than a cylinder does, as the mass is located further away from its rotational axis. - A upright broom is easier to balance when the heavier end is o Nearest your hand - It is easier to run with bend legs than with straight less due to o Rotational inertia - Angular momentum= rotational inertia* rotational velocity - Angular momentum is a conserved quantity. Therefore the product and I and w has to be constant. - Why does a typical helicopter have two motors? o They go different ways to help balance each other out. - A large wheel is coupled to a wheel with half of the diameter. Rotational speed? Tangential speed at the rims? o Larger wheel has pedals because it takes ½ the amount of time to rotate. Therefore, we will move more quickly. - Angular speed is conserved. - What happens, if you move the mass the left/right? o Torque ▪ A torque balance used to measure weight ▪ Torque= lever arm * force - Force causes acceleration - Torque causes rotation o Equal and opposite - No rotation is produced when the torques balance each other. - Simple machine o Work in= work out - The center of mass can be outside the mass of a body o DONUT, BANANA - Center of mass is still under the support - When you stand, your feet somewhere above the base area bound your center of gravity. Why do you keep you legs far apart when you have to stand in the aisle of a bumpy riding bus? - You can lean over and touch your toes without falling over only if your center of gravity is above the area bounded by your feet. - Why do hurricanes spin counter-clock wise? o Earth rotates clockwise, due to the Corolis effect. The hurricane spins counter-clockwise. Linear velocity is greatest at the equator. Clicker and Homework Questions 1. If a turntable’s rotational speed is doubled, then the linear speed of a pet hamster sitting on the edge of the record will Double 2. Horses that move with the fastest linear speed on a merry-go-round are located Near
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