What is energy? In science, energy is the ability to do work. Work is done when a force causes an object to move in the direction of the force. Energy is expressed in units of joules (J). A joule is calculated as force x distance, so 1J = 1Nm Energy is conserved in all cases. Because no exception to this rule has been found, this rule is described as a law. According to the law of conservation of energy, energy cannot be created or destroyed. The total amount of energy in a closed system is always the same. Kinetic energy is the energy an object has due to its motion. Kinetic energy depends on both mass and velocity. The faster an object moves, the more kinetic energy it has. The greater the mass of a moving object, the more kinetic energy it has. Potential energy is stored energy. Potential energy can be stored in the chemical bonds of fuel, the nucleus of atom, foods, electric charge, and in other factors. Potential energy can also be stored because of the work done on it. For example: stretching a rubber band, winding a watch, pulling back on a bowstring, and lifting a brick high in the air. When a raised object is released gravitational potential energy is converted into kinetic energy. If there is no significant air resistance, then conservation of energy results in gravitational potential energy being converted into kinetic energy as an object falls. The gain in kinetic energy equals the loss of gravitational potential energy.
Roller coasters work because of the energy that is built into the system. Initially, the cars are pulled mechanically up the tallest hill, giving them a great deal of potential energy. From that point, the conversion between potential and kinetic energy powers the cars throughout the entire ride. Equations: Kinetic energy = KE Potential Energy = PE KE = (mass x velocity 2 ) 2 PE = force x distance KE = (mv 2 ) 2 PE = Fd m = ( 2KE) v 2 GPE = mgh or GPE = wh v = ((2KE) m) w = GPE h h = GPE w What is the kinetic energy of a car that has a mass of 2,400kg and is moving at 20m/s? What is the kinetic energy of a 4,000kg elephant that is running at 2m/s? If a bus is moving at 30m/s and has a mass of 2,000kg, what is it s kinetic energy?
What is the gravitational potential energy of a cat that weighs 40N standing on a table that is 0.8m above the ground? What is the gravitational potential energy of a diver who weighs 500N standing on a platform that is 10m above the pool? What is the kinetic energy of a 400,000kg jet flying at 72m/s? What is the gravitational potential energy of a cantaloupe with a mass of 4kg and a height of 12 meters? Distinguish among forms of energy All matter is made of particles that are always in motion. Thermal energy (heat) is the internal energy in substances; it is the vibration and movement of atoms and molecules within substances. Objects with a higher temperature have more thermal energy because their particles are moving faster. However, objects with a greater mass, but a lower temperature, may have more thermal energy because they have more particles. Think of an iceberg versus a cup of hot chocolate. Geothermal energy is an example of thermal energy. Chemical energy is the energy that is stored in the chemical bonds of atoms and molecules. As the bonds are broken, energy is released. Nuclear energy is the
energy stored in the nucleus of an atom. It is the energy that holds the nucleus together. The nucleus of a uranium atom is an example of nuclear energy. Radiant energy is the electromagnetic energy that travels in transverse waves. Radiant energy includes visible light, x-rays, and radio waves. Solar energy is an example of radiant energy. Sound is the movement of energy through substances in longitudinal (compression/rarefaction) waves. Electrical energy is the energy of moving electrons. As the electrons move, they can be used to do work with electrical devices. Lightning and electricity are examples of electrical energy. Mechanical energy is the total energy of motion and position of an object. Both potential energy and kinetic energy are kinds of mechanical energy. Mechanical energy = potential energy + kinetic energy. Elastic potential energy is stored mechanical energy in objects by the application of force. Compressed springs and stretched rubber bands are examples of elastic potential energy. Gravitational potential energy is the energy stored when an object is lifted upwards. This energy is released when the object falls back to its initial position. Water in a reservoir behind a hydropower dam is an example of gravitational potential energy. When the water is released to spin the turbines, it becomes kinetic energy. The movement of objects or substances from one place to another is kinetic mechanical energy. Wind and hydropower are examples of kinetic mechanical energy.
Forms of Energy All forms of energy fall under two categories Potential Energy Potential energy is stored energy and energy of position Kinetic Energy Kinetic energy is energy of motion. It is the motion of waves, electrons, atoms, molecules, and substances. Chemical Energy The energy stored in the bonds of atoms and molecules. Includes biomass, petroleum, natural gas, and coal. Radiant Energy Electromagnetic energy that travels in transverse waves. Includes light, x-rays, and radio waves. Nuclear Energy The energy stored in the nucleus of an atom. It is the energy that holds the nucleus together. Includes the nucleus of the uranium atom. Thermal Energy The energy or heat found in the internal energy in substances; it is the vibration and movement of atoms and molecules within substances. Includes geothermal energy. Stored Mechanical Energy The energy stored in objects by the application of force. Includes compressed springs and stretched rubber bands. Motion The movement of objects or substances from one place to another is motion. Includes wind and hydropower. Gravitational Energy The energy of place or position. Water in a reservoir behind a dam and a book on a shelf are examples. Sound The movement of energy through substances in longitudinal waves (compression and rarefaction) waves. Electrical Energy The movement of electrons. Lightning and electricity are examples.
Energy resources When the nucleus splits (fission), nuclear energy is released in the form of heat energy and light energy. Nuclear energy is also released when nuclei collide at high speeds and join (fusion). Wind power is used to rotate a turbine (the blades) which turns an electrical generator. Hydroelectric power uses falling water is used to drive a turbine which rotates an electrical generator. Tidal Power uses moving water caused by the tides to drive a turbine directly which rotates an electrical generator. Geothermal Energy is thermal energy caused by the heating of the Earth s crust. Solar Energy can be used as thermal and radiant energy. Solar heating is when thermal heat energy from the sun is focussed onto pipes containing water. The water boils producing steam. The steam is then used to drive turbines which turn electrical generators. Solar cells produce electricity directly from the sun s radiation. Fossil Fuels are an energy resource formed from the remains of organisms that lived long ago, includes coal, oil, and natural gas. Biomass is biological material derived from living, or recently living organisms. The vital difference between biomass and fossil fuels is one of time scale. Most of our electricity is produced by thermal power stations. These use the heat produced by burning fuels or the fission of uranium to generate electricity.
The heat produced is used to change water into high pressure steam. This steam is used to turn a turbine which in turn rotates an electrical generator. Over 90% of our electricity is generated by using thermal power stations. U.S. Energy Consumption Energy Resources Gas 28% Coal 18% Petroleum 35% Nuclear 8% Renewable 10% Biomass 5% Wind & Solar 2% Hydro 2.6%