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Energy. Definition: In general, the word energy refers to a concept that can be defined as " the potential for causing changes ", and therefore one can say that energy is the cause of any change. Forms of Energy.
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Energy Definition: In general, the word energy refers to a concept that can be defined as "the potential for causing changes", and therefore one can say that energy is the cause of any change
Forms of Energy • Energy is found in different forms, such as light, heat, sound and motion. There are many forms of energy, but they can all be put into two categories: kinetic and potential.
KINETIC ENERGY • Kinetic energy is motion of waves, electrons, atoms, molecules, substances, and objects.
Electrical Energy • Is the movement of electrical charges. Everything is made of tiny particles called atoms. Atoms are made of even smaller particles called electrons, protons, and neutrons. Applying a force can make some of the electrons move. Electrical charges moving through a wire is called electricity.
Radiant Energy • Is electromagnetic energy that travels in the space. Radiant energy includes visible light, x-rays, radio waves and gamma rays. • Solar energy is an example of radiant energy.
Thermal Energy • Thermal energy or heat, is the internal energy in substances • Geothermal energy is an example of thermal energy.
Motion Energy • Is the movement of objects and substances from one place to another.. Wind is an example of motion energy • Objects and substances move when a force is applied according to Newton’s Laws of Motion F = M*a
POTENTIAL ENERGY • Potential energy is stored energy and the energy of position––gravitational energy. There are several forms of potential energy. Chemical Energy. Stored Mechanical Energy Nuclear Energy. Gravitational Energy
Chemical Energy • Is energy stored in the bonds of atoms and molecules. It is the energy that holds these particles together. Biomass, petroleum, natural gas, and propane are examples of stored chemical energy.
Stored Mechanical Energy • Is energy stored in objects by the application of a force. Compressed springs and stretched rubber bands are examples of stored mechanical energy
Nuclear Energy Is energy stored in the nucleus of an atom The energy that holds the nucleus together can be released when the nuclei is split apart. Nuclear power plants split the nuclei of uranium atoms in a process called fission.
Nuclear Energy • nuclear fusion is the process by which multiple nuclei join together. Later we have a heavier nucleus and the release of energy • Scientists are working on creating fusion energy, so that someday there might be fusion power plants.
Gravitational Energy • Is the energy of positionor place. • A rock resting at the top of a hill contains gravitational potential energy. • Hydropower, such as water in a reservoir behind a dam, is an example of gravitational potential energy.
Conservation of energy • The law of conservation of energy says that energy is neither created nor destroyed. When we use energy, it doesn’t disappear. We change it from one form of energy into another.
Conservation of energy • Energy cannot be created or destroyed but can only be transferred from one body to another or change from one form to another. • A car engine burns gasoline, converting the chemical energy in gasoline into mechanical energy. Solar cells change radiant energy into electrical energy.
Energy Units and Conversions • In the International System, energy is measured in joules • Joule (J) is the unit of energy, equal to the force of one Newton acting through one meter. • 1J = 1N*1mThere is another energy units, the calorie • 1 calorie of heat is the amount needed to raise 1 gram of water 1 degree Centigrade. • 1 calorie (cal) = 4.184 J
Energy Units and Conversions • Calculate how many calories are: • a) 2005 joules • b) 3566 joules • Calculate how many joules are • A) 34545 calories • B) 5664 calories
Energy Units and Conversions • Find the work (energy) done when a horse exert a horizontal force of 400 N on a cart and pulls it 20 m in the direction of the force
Mechanical power • Power is the rate at which work is done. • Power = work done / time taken. • The measured of power is watt ( W) • So if time is measured in seconds and work in Jules: • 1W = 1J/1s
Exercices • Exercices 1º • A car engine provides a forward force of 1000 N. If the car is travelling at 20 m s-1, what power is developed? • Remember that: • work = Force multiplied by distance or • W = F*D
Exercices Solution • In 1 s, the car travels 20 m. Hence we can calculate: • Work done in 1 s = force × distance = 1000 N × 20 m = 20 000 J = 20 kJ • Power = work done / time taken = 20 kJ / 1 s = 20 kW.
Exercices 2 A man raises a object of mass 40 kg through a vertical height of 20 m in 4 seconds. Find the power. Note: The potential energy is measured by the following equation: Pe = m x g x h Where: M = mass , g = 9,8 , h = height Solution: 1960 W
Exercices 3 • A women run up a flight of 120 stairs in 30 seconds. If the height of each stair is 15 cm, find the power • Solution: 294 watts
Exercices 4 4.1) A 100 watt electric heater is used to heat water and bring it to the boil. If 5000 j are needed to bring the water to the boil, for how long is the heater operating? • 4.2) How much energy is given out by a 60W bulb the is running 5 hours?
