Chapter 15 Energy

Energy is the ability to do work Work and energy are closely related. When work is done on an object, energy is transferred to that object. Energy is the ability to do work Work is a transfer of energy Work and energy are typically measured in joules

Energy is classified into two general types: Kinetic Energy 2. Potential Energy

Kinetic Energy Kinetic comes from the Greek work kinetos, meaning “moving” Kinetic energy of a moving object depends upon its mass and speed 1 mv2 Kinetic Energy = 2

1 A 70.0 kilogram man is walking at a speed of 2.0 m/s. What is his kinetic energy? mv2 KE = 2 1 KE = (70.0 kg) (2.0 m/s)2 2 1 (70.0 kg) (4.0 m2/s2) KE = 2 KE = 140 kg x m2/s2 or 140 Joules

1 A 1400 kilogram car is moving at a speed of 25 m/s. How much kinetic energy does the car have? KE = mv2 2 1 (1400 kg) (25 m/s)2 KE = 2 1 KE = (1400 kg) (625 m2/s2) 2 KE = 437,500 kg x m2/s2 or 437,500 Joules

Energy that is stored as a result of position or shape Potential Energy Energy that is stored as a result of position or shape Two forms of potential energy are: Gravitational potential energy Elastic potential energy

Gravitational Potential Energy Potential energy that depends on an object’s height is called gravitational potential energy Gravitational PE Depends on the object’s mass, height, and acceleration due to gravity. Potential Energy (PE) = mgh

A diver at the top of a 10.0 meter-high diving platform has a mass of 50.0 kilograms. What is her potential energy relative to the ground? PE = mgh PE = (50.0 kg) ( 9.8 m/s2) (10.0 m) PE = 4900 kg x m2/s2 or 4900 Joules (J)

A 6 kilogram object is resting on top of a bookshelf that is 2 meters high. What is the object’s gravitational potential energy relative to the floor? PE = mgh PE = (6 kg) (9.8 m/s2) (2 m) PE = 117.6 kg x m2/s2 or 117.6 J

Elastic Potential Energy Energy of an object that has been stretched or compressed Something is elastic if it springs back to its original shape when it is stretched or compressed Examples: Rubber bands, strings on instruments, balls that bounce, or springs

Main Forms of Energy Mechanical Energy Thermal Energy Chemical Energy Electrical Energy Electromagnetic Energy Nuclear Energy

Mechanical Energy = Potential Energy and Kinetic Energy Energy associated with the motion and position of everyday objects (not limited to machines) Mechanical Energy = Potential Energy and Kinetic Energy ME = PE + KE

Energy Conversion Calculations If friction is small enough to be ignored and no mechanical energy is added to a system then…. (KE + PE) beginning = (KE + PE) end

2. Thermal Energy Particles (atoms) are always in random motion Total PE and KE related to the motion of microscopic particles makes up thermal energy Atoms move faster - Thermal energy increases - Temperature increases Atoms move slower - Thermal energy decreases - Temperature decreases

3. Chemical Energy Energy stored in chemical bonds When chemical bonds are broken, the energy is released Examples: Wood, gasoline, cellular respiration of sugar, elephant toothpaste reaction

4. Electrical Energy Energy associated with electrical charges ( + and - ) Examples: Batteries or lightning bolts

5. Electromagnetic Energy Form of energy that travels through space in the form of waves Because of their ability to travel long distances, they are often used in communication Examples: Visible light and X-rays

The energy is harnessed by the fission (splitting) of atomic nuclei 6. Nuclear Energy The energy stored in the nucleus of an atom (Due to strong and weak nuclear forces) The energy is harnessed by the fission (splitting) of atomic nuclei The fusion (joining) of atomic nuclei is also a form of nuclear energy

Energy can be converted from one form to another The law of conservation of energy states that energy cannot be created or destroyed