However, because kinetic energy is given by K = 1 2 m v 2 K = 1 2 m v 2, and velocity is a quantity that is different for every point on a rotating body about an axis, it makes sense to find a way to write kinetic energy in terms of the variable ω ω, which is the same for all points on a rigid rotating body. (credit: Zachary David Bell, US Navy)Įnergy in rotational motion is not a new form of energy rather, it is the energy associated with rotational motion, the same as kinetic energy in translational motion. However, most of this energy is in the form of rotational kinetic energy.įigure 10.17 The rotational kinetic energy of the grindstone is converted to heat, light, sound, and vibration. This system has considerable energy, some of it in the form of heat, light, sound, and vibration. Sparks are flying, and noise and vibration are generated as the grindstone does its work. Figure 10.17 shows an example of a very energetic rotating body: an electric grindstone propelled by a motor.
However, we can make use of angular velocity-which is the same for the entire rigid body-to express the kinetic energy for a rotating object. We know how to calculate this for a body undergoing translational motion, but how about for a rigid body undergoing rotation? This might seem complicated because each point on the rigid body has a different velocity. Rotational Kinetic EnergyĪny moving object has kinetic energy. With these properties defined, we will have two important tools we need for analyzing rotational dynamics. In this section, we define two new quantities that are helpful for analyzing properties of rotating objects: moment of inertia and rotational kinetic energy. So far in this chapter, we have been working with rotational kinematics: the description of motion for a rotating rigid body with a fixed axis of rotation.
Define the physical concept of moment of inertia in terms of the mass distribution from the rotational axis.Describe the differences between rotational and translational kinetic energy.By the end of this section, you will be able to:
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