2. Work – Force X Distance Energy is what makes things move. When you move something you do work. The amount of energy it takes to move something depends on the force exerted and the distance it is moved. Work (change in energy)= force X distance Impulse (change in momentum) = force X time. Ex: Lift a barbell over your head = work is done on barbell Hold the barbell over your head ≠ work is not done on barbell Units for work: Newtons x meters (N∙m) 1 N∙mis equal to 1 joule – the energy to pick up a ¼ pound cheeseburger from the table to above your head.
3. Power – How Quickly Work Gets Done Power is the rate at which work is done. Power = work done time The unit of power is the joule per second (j/s), or the watt (W). Ex: One watt of power is used if you lift that cheeseburger in one second. 1kilowatt (kW) is 1000 watts, 1 megawatt (MW) is 1,000,000 watts.
4. Mechanical Energy Mechanical energy is the ability to do work on an object (make it move) The unit it ismeasured in is joules (j). Mechanical energy (work) can be in the form of potential and/or kinetic energy.
5. Potential Energy – Stored Energy Potential Energy (PE) is energy that is stored in ready position and has the potential to do work. Work = force x distance Gravitational PE = weight x height. PE = mass x gravity x height (mgh) Ex. A rock at the top of a hill, a bow pulled back, a compressed spring.
6. Kinetic Energy – Energy of Motion Kinetic Energy (KE) depends on an object’s mass and speed. KE = ½ mass x speed2 (½mv2) Ex. A moving car has kinetic energy, a car moving twice as fat twice the speed has 2v2or four times the KE. To change the kinetic energy of an object work must be done on it. The change in kinetic energy (∆KE) = Work
7. Conservation of Energy Energy comes in many forms: heat, light, sound, electricity, and radioactivity. The law of conservation of energy: Energy cannot be created or destroyed; it may be transformed from one form into another, or transferred from one object to another, but the total amount of energy never changes. Ex. Eat a cheeseburger (chemical energy) -> body heat.
