Download
1 / 32
320 likes | 573 Views
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. When one object does work on another, energy is transferred from the first object to the second object. This energy allows the second object to do work.
E N D
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. When one object does work on another, energy is transferred from the first object to the second object. This energy allows the second object to do work. Therefore… work is a transfer of energy. Work is expressed in units of joules (J).
Kinetic Energy • the energy of an object due to the object’s motion • ALL moving objects have • kinetic energy! • it can be used to do work • (example: allows a hammer • to do work on a nail) Kinetic energy = mass x (speed)2 2
Potential Energy • the energy an object has because of its position, shape, or condition of the object • stretched bow = bow has • energy because work has • been done to change its shape. • The energy of that work has • been changed into potential.
Gravitational Potential Energy • When you lift an object, you do work on it. • You use a force that is against the force of gravity. • When you do this, you transfer • energy to the object and give • it gravitational potential energy. • The amount of GPE that an • object has depends on its • weight and height. GPE = weight x height
Mechanical Energy • the amount of work an object can do because of the object’s kinetic and potential energies • the total energy of motion • and position of an object • potential and kinetic are • kinds of mechanical energy Mechanical energy = potential energy + kinetic energy
THERMAL ENERGY • all the kinetic energy due to random motion of the particles that make up an object • Particles move faster at higher temperatures • The faster the • particles move, the • greater their kinetic • energy and the greater • the object’s thermal • energy
The illustration shows how matter changes its state by the addition of thermal energy.
CHEMICAL ENERGY • the energy of a compound • that changes as its • atoms are rearranged • a form of potential energy
ELECTRICAL ENERGY • The energy of moving electrons • Electrons are the negatively charged particles of atoms • The electrical energy of moving electrons is used to make the sound you hear from an amplifier • Electrical energy in your home comes from power plants that use huge generators to turn magnets inside loops of wire. The changing position of the magnet makes electrical energy run through he wire is used when you plug something into an outlet.
SOUND ENERGY • caused by an object’s vibrations • stretched guitar string = stores potential energy • let the guitar string go = kinetic energy which makes string vibrate
LIGHT ENERGY • Produced by the vibrations of electrically charged particles • Light vibrations cause energy to be transmitted, but the vibrations that transmit light energy don’t need to be carried through matter • Light energy can move through a vacuum (an area where there is no matter)
NUCLEAR ENERGY • Energy that comes from the nucleus of an atom • Fusion = joining 2 hydrogen nuclei together to make a larger helium atom (the sun) • Fission – the nucleus of uranium is split apart (Perry Nuclear Power Plant)
ENERGY CONVERSIONS a change from one form of energy to another Kinetic and Potential Energy
Elastic Potential Energy • Energy stored in a rubber band (or elastic object) • A wound up rubber band in a toy airplane has potential energy – when it is let go the stored energy becomes kinetic, spins the propeller and makes the airplane fly
CONVERSIONS INVOLVING CHEMICAL ENERGY • Chemical energy comes from the food you eat • Chemical energy in food is converted into kinetic energy when you are active. It is converted into thermal energy to maintain body temperature.
ENERGY CONVERSIONS IN PLANTS • Chemical energy in food you eat comes from the sun’s energy! • Photosynthesis uses light energy to make new substances that have chemical energy. • Chemical energy in trees can be converted into thermal when wood is burned.
WHY ENERGY CONVERSIONS ARE IMPORTANT Needed for everything we do! Machines like hair dryers : electrical energy alone won’t dry your hair – converts into heat energy
ENERGY AND MACHINES A machine can make work easier by changing the size or direction (or both) of the force needed to do work. Many simple machines use energy transferred by the person/animal
MACHINES AND ENERGY CONVERTERS Machines help you use energy by converting it into the form you need. Radiometers – measures energy from the sun Converts light energy into heat energy into kinetic energy http://www.youtube.com Radiometer
CONSERVATION OF ENERGY friction: a force that opposes motion between two surfaces that are touching
For a roller coaster to move, energy must be used to overcome friction. There is friction between the cars’ wheels and the track between the cars and the air around them. As a result, not all the potential energy of the cars changes into kinetic energy as the cars go down the first hill. AND…not all of the kinetic energy of the cars changes back into potential energy.
PE is greatest at the top of the first hill. PE at the top of the second hill is less than KE and PE from the first hill. KE at the bottom of the first hill is less than the PE at the top was.
Energy is Conserved within a Closed System A closed system is a group of objects that transfer energy only to each other. Example roller coaster = track, cars & the air around them
Some mechanical energy is converted into thermal energy because of friction. Sound energy also comes from the energy conversions in a roller coaster. If you add the cars’ kinetic energy at the bottom of the first hill, the thermal energy due to overcoming friction and the sound energy made = the total amount of potential energy So energy is conserved – NOT LOST!
Law of Conservation of Energy Energy cannot be created or destroyed!
Some energy is converted into thermal energy, which makes the bulb feel warm. Some electrical energy is converted into light. As electrical energy is carried through the wires, some of it is converted in to thermal energy.
Any time one form of energy is converted into another form, some of the original energy always gets converted in to thermal energy. This is not useful energy! = Not used to do work! Not all the gasoline’s chemical energy makes the car move. Some wasted thermal energy will always result from the energy conversions. Much of it leaves through the radiator and exhaust pipe.
Perpetual Motion? No Way! It is impossible to create a machine that will run forever = put out exactly as much energy as it takes in. The only way a machine can keep moving is to have a constant supply of energy. DRINKING BIRD Uses thermal energy from the air to evaporate the water from its head…not a perpetual motion machine!
MAKING CONVERSIONS EFFICIENT Energy Efficient = comparison of the amount of energy before a conversion with the amount of useful energy after the conversion.
