Potential and Kinetic Energy

What is Energy Energy is the ability to do work. Measured in Joules (J). Mechanical energy is the energy due to the position of something or the movement of something. Energy is never created or destroyed, it is only transformed into a different form.

Forms of Energy Chemical - gasoline Electrical - lightning Heat – burner on a stove Light – flash light Mechanical - car Nuclear - sun Sound – music on the radio

Potential and Kinetic Energy Mechanical Energy What are the two forms of mechanical energy? Potential and Kinetic Energy Energy that is stored is called potential energy (PE) because in the stored state it has the potential for doing work. Three examples of potential energy are elastic potential energy, chemical energy, and gravitational potential energy.

Examples of Potential Energy: A stretched rubber band.. Water at the top of a waterfall.. Yo–Yo held in your hand.. A drawn Bow and Arrow…

Potential Energy Work is required to elevate objects against Earth’s gravity. The potential energy due to elevated positions is gravitational potential energy (GPE). The higher an object, the more potential energy. The more mass an object has, the more potential energy it has.

Potential Energy The amount of gravitational potential energy possessed by an elevated object is equal to the work done against gravity to lift it. GPE = mgh The height is the distance above some chosen reference level, such as the ground or the floor.

Potential Energy The potential energy of the 100-N boulder with respect to the ground below is 200 J in each case. The boulder is lifted with 100 N of force. The boulder is pushed up the 4-m incline with 50 N of force. The boulder is lifted with 100 N of force up each 0.5-m stair.

Kinetic Energy When stored energy begins to move, the object now transfers from potential energy into kinetic energy.

Kinetic Energy If an object is moving, it has energy. (Be careful, the converse of this statement is not always true!) This energy is called kinetic energy - the energy of motion.

Kinetic Energy An object’s kinetic energy depends on: the object’s mass. Kinetic energy is directly proportional to mass. the object’s speed (velocity). Kinetic energy is directly proportional to the square of the object’s speed.

Potential Energy Check If I want to drop an apple from the top of one of these three things, where will be the most potential energy? A C B Since the tower is the highest off the ground, the apple would have the most PE (PE = mgh)

Kinetic Energy Check When these objects move at the same speed, which will have more kinetic energy? The truck will have a higher KE at the same speed because it has a larger mass KE = ½ mv2

Work – Energy Theorem When you throw a ball, you do work on it to give it speed as it leaves your hand. The moving ball can then hit something and push it, doing work on what it hits. Common units of kinetic energy: Joules

Work – Energy Theorem The work-energy theorem describes the relationship between work and energy. Work = ∆KE; ΔPE = -Work Work equals the change in kinetic energy. The work in this equation is the net work—that is, the work based on the net force.