Energy

Energy and Work Energy – the ability to do work Work is a transfer of energy Energy is also measured in Joules

Kinetic Energy Kinetic energy – energy of an object’s motion Depends on mass and speed Equation: Kinetic energy (KE) = ½ mv 2

Kinetic Energy Example A 0.10 kg bird is flying at a constant speed of 8 m/s. What is the bird’s kinetic energy? m = 0.10 kgKE = ½ (0.10)(8 2 ) v = 8 m/sKE = ½ (0.10)(64) KE = ?KE = ½ (6.4) KE = 3.2 J

Potential Energy Potential energy – stored energy Energy of an object that is not moving Gravitational potential energy – depends on an object’s height and weight (mass and acceleration of gravity) Gravitational potential energy equation Potential energy (PE) = mgh mg = weight m = mass g = gravity (9.8 m/s 2 ) h = height

Potential Energy Example A diver with a mass of 50.0 kg is at the top of a 10.0 m high diving board. What is her potential energy relative to the ground? m = 50.0 kg PE = (50.0 kg)(9.8 m/s 2 )(10.0 m) g = 9.8 m/s 2 PE = 4900 J h = 10.0 m PE = ? If the diver stands on the ground instead of the diving board, what is his/her potential energy relative to the ground? Zero because the height from the ground is zero

Potential Energy Cont’d… Elastic potential energy – energy of a stationary object that is being stretched or compressed Ex: rubber bands, springs

Forms of Energy Mechanical Energy – motion and position of everyday objects Sum of KE and PE Thermal Energy – PE and KE of atoms of an object Related to heat Chemical Energy – energy stored in chemical bonds Electrical Energy – associated with electrical charges Electromagnetic Energy – form of energy that travels through space in the form of waves Ex: x-rays, UV waves Nuclear Energy – stored in an atom’s nucleus

Energy Conversion Energy can change from one form to another Ex: light bulbs Electrical energy can be converted to thermal energy

Conservation of Energy Law of Conservation of Energy – energy cannot be created nor destroyed It can only change forms!