Energy in a Mechanical System

1. Energy in a Mechanical System 5.1

2. Definitions: Property—quality or trait belonging to the system Energy—the ability to do work Kinetic energy—energy of motion Internal energy—sum of the microscopic kinetic and potential energies of all the atoms and molecules that make up a system Total energy—the sum of kinetic, potential, and internal energies of an object or system Law of conservation of energy—energy cannot be created nor destroyed; it can change form

3. Kinetic Energy • A. • B. Kinetic energy = ½ mass x speed2 • C. Unit for energy the same as for work—Joules, foot-pounds

4. Kinetic Energy in Rotational Systems • A. Moment of inertia • 1. A measure of a body's resistance to angular acceleration, equal to: the product of the mass of a particle and the square of its distance from a reference • 2. I • 3. • 4. Kinetic energy = ½ (moment of inertia) (angular speed)2

5. 5. center of mass—measure from that point 6. The moment of inertia of an object is the sum of the moments of all the particles that make up the object. 7. p. 235—formulas for moments of inertia for different-shaped objects.

6. III. The Work-Energy Theorem A. Work—a measure of the energy that is transmitted by a force, such as a contact, gravitational, electrical, or magnetic force. B. Example: a skater striking a hockey puck with a stick C. W = ΔKE