Work and Energy

1. Work and Energy What is Energy Kinetic Energy Work Work-Kinetic Energy Theorem Gravitational Potential Energy Spring Potential Energy Work Done by a Variable Force Power pps by C Gliniewicz

2. Energy is a scalar quantity associated with the state of an object. It is a conserved quantity which measures the ability to do work. Kinetic energy is energy associated with the state of motion of an object. An object at rest has no kinetic energy. An object which is moving at non-relativistic speeds, well below the speed of light has kinetic energy. The SI unit of energy is the joule. The transfer of energy via a force is called work. To do work, a force has to be applied to an object and the object has to move in the direction of the force. Energy that is transferred to the object is positive energy and energy transferred from the object is negative energy. Work is also considered positive if the object moves in the direction of the force and negative if it is in the opposite direction of the force. pps by C Gliniewicz

3. The net work done by a number of forces can be determined by finding the work done by each force and then summing the work. Also, one could sum the forces first and find the displacement. Then one could find the net work done. The Work-Kinetic Energy Theorem states that the change in the kinetic energy is equal to the work done. Gravity does work when an object is moved in the direction of the gravitational force. The work done by gravity is positive if the object moves downward. The work done by gravity is negative if the object moves upward. If an object is lifted vertically, then the change in kinetic energy has to be equal to the sum of the work done by the force and the work done by gravity. If there is no change in kinetic energy, the work done by the force is equal to the work done by gravity. pps by C Gliniewicz

4. Work can be done by a spring which is compressed or stretched. Robert Hooke did experiments with springs and determined that the force needed to stretch or compress a spring was related to the distance the spring is compressed or stretched. The work done by a spring is the integral of the force times the distance. The work done by the spring is positive if the block ends up closer to the relaxed position and is negative if the block ends up farther away from the relaxed position. The work done by the applied force is opposite that of the spring. If work is done in three dimensions, then the work is the sum of the work is each dimension. Power is the rate of change of work with respect to time. pps by C Gliniewicz