Potential and Kinetic Energy

Energy! All objects need energy to move! unit is Joules (J) Objects must store energy to be able to move later You store energy by _________ You store energy by _________ You use energy to 1) You use energy to 1) 2) 2) 3) 3)

How is all energy divided? Potential Energy Kinetic Energy All Energy Gravitation Potential Energy Elastic Potential Energy Chemical Potential Energy

What is Potential Energy? oEnergy that is stored and waiting to be used later oThe more energy an objects stores, the more movement it may have! oP.E. = mass x gravity x height

What is Gravitational Potential Energy? oPotential energy due to an object’s position The higher up you are, the more stored energy you have! Don’t look down,Rover!Good boy!Don’t look down,Rover!Good boy!

What is Elastic Potential Energy? oPotential energy due compression or expansion of an elastic object. Notice the ball compressing and expanding

What is Chemical Potential Energy? oPotential energy stored within the chemical bonds of an object

What is Kinetic Energy? oEnergy used during motion oK.E. = ½ x mass x velocity 2

Work and Power

Work A force acting upon an object to cause a displacement ( (A force causes an object to MOVE!) For a force to qualify it must For a force to qualify it must 1. Displacement MUST happen 2. Force MUST cause the displacement What are some examples of work?

Examples a horse pulling a plow through the fields a horse pulling a plow through the fields a father pushing a grocery cart down the aisle of a grocery store a father pushing a grocery cart down the aisle of a grocery store (Hmmmm… work or a miracle?) a freshman lifting a backpack full of books upon her shoulder a freshman lifting a backpack full of books upon her shoulder (would a junior do work like this?) a weightlifter lifting a barbell above her head a weightlifter lifting a barbell above her head a shot-put launching the shot, etc. a shot-put launching the shot, etc.

Work or NOT? A teacher applies a force to a wall and becomes exhausted.A teacher applies a force to a wall and becomes exhausted. No. The wall is not displaced. A book falls off a table and free falls to the ground.A book falls off a table and free falls to the ground. Yes! The is a downward force (gravity) which acts on the book to displace it.Yes! The is a downward force (gravity) which acts on the book to displace it. A waiter carries a tray full of meals above his head by one arm across the room.A waiter carries a tray full of meals above his head by one arm across the room. No. There is an upward force, and there is a horizontal displacement but the force does not cause the displacementNo. There is an upward force, and there is a horizontal displacement but the force does not cause the displacement A rocket accelerates through space.A rocket accelerates through space. Yes the expelled gas is the force which accelerates the rocket through space.

Work Solving for work Work = force x distance (J) (N) (m) (J) (N) (m) ****If you are given mass (kg), you must find the FORCE of weight FIRST!! ****If you are given mass (kg), you must find the FORCE of weight FIRST!! weight = mass x gravity weight = mass x gravity

Power A measure of work done in a period of time Power = work / time (watts) (J) (s) (watts) (J) (s)