Energy Chapter 15

Energy and Its Forms Section 15-1

Energy and Work Energy is the ability to do work. Work is a transfer of energy. Both work and energy are measured in joules

Kinetic Energy The energy of motion The kinetic energy of any moving object depends on its mass and speed. KE = ½ mv2

Let’s try one… A 0.10 kilogram bird is flying at a constant speed of 8.0 m/s. What is the birds kinetic energy? KE = ½ mv2 KE = ½ (0.10 kg)(8.0m/s)2 KE = 3.2 kg·m2/s2= 3.2 Joules

Potential Energy The energy stored as a result of position or shape An object’s gravitational potential energy depends on its mass, its height, and the acceleration due to gravity. Elastic potential energy is the potential energy of an object that is stretched or compressed.

Let’s Calculate Gravitational Potential Energy A diver is at the top of a 10.0 meter high diving platform has a mass of 50.0 kilograms. Calculate her potential energy. PE = mgh PE = 50.0 kg (9.8 m/s2)(10.0 m) PE = 4900 kg· m2/s2 = 4900 J

Forms of Energy The major forms of energy are mechanical energy, thermal energy, chemical energy, electrical energy, electromagnetic energy, and nuclear energy.

Forms of Energy Mechanical Energy – the energy associated with the motion and position of everyday objects. Thermal Energy – since atoms are in constant motion, all matter has kinetic energy. The total potential and kinetic energy of all microscopic particles in an object make up its thermal energy.

Forms of Energy Chemical Energy – the energy stored in chemical bonds Electrical Energy – the energy associated with electrical charges

Forms of Energy Electromagnetic Energy – a form of energy that travels through space in the form of waves Nuclear Energy – the energy stored in atomic nuclei

Energy Conversion & Conservation Section 15-2

Energy Conversion Energy can be converted from one form to another. Energy conversion – the process of changing energy from one form to another

Conservation of Energy The law of the conservation of energy states that energy can not be created or destroyed When a moving objects stops moving due to friction, its kinetic energy is turned into thermal energy.

Energy Conversions The gravitational potential energy of an object is converted to the kinetic energy of motion as the object falls. Pendulums & Pole Vaulters

Energy & Mass Einstein’s equation, E=mc2, says that energy and mass are equivalent and can be converted into each other. Since c is a very big number (3 x 108), this formula shows that a small amount of mass can make a lot of energy!

Energy Resources Section 15-3

Nonrenewable Energy Resources Nonrenewable Energy Resources – energy resources that exist in limited quantities and, once used, cannot be replaced except over the course of millions of years. This includes fossil fuels (oil, natural gas, coal), and uranium.

Renewable Energy Resources Renewable Energy Resources – energy resources that can be replaced in a relatively short period of time This includes hydroelectric, solar, geothermal, wind, biomass, and possible in the future, nuclear fusion.

Renewable Energy Resources Hydroelectric energy – energy obtained from flowing water Solar energy – sunlight that is converted into usable energy Geothermal energy – thermal energy beneath Earth’s surface

Other Renewable Resources Biomass energy – the chemical energy stored in living things Hydrogen fuel cell – generates electricity by reacting hydrogen with oxygen

Conserving Energy Resources Energy resources can be conserved by reducing energy needs and by increasing the efficiency of energy use. Energy conservation – finding ways to use less energy or to use energy more efficiently