Transcript energy
ENERGY Energy Is the Ability To Do Work There are many forms of energy, but they can all be put into two categories: potential and kinetic. Modern civilization is possible because man has learned how to change energy from one form to another and use it to do work. Potential Energy: Potential energy is stored energy . • Gravitational Potential Energy is energy stored in an object's height. The higher and heavier the object, the more gravitational energy is stored. – When you ride a bicycle down a steep hill and pick up speed, the gravitational energy is being converted to motion energy. – Hydropower is another example of gravitational energy, where the dam "piles" up water from a river into a reservoir. Other forms of Potential Energy: Potential energy is stored energy. There are several forms of potential energy. 1. Chemical Energy is energy stored in the bonds of atoms and molecules. Biomass, petroleum, natural gas, and coal are examples of stored chemical energy. Chemical energy is converted to thermal energy when we burn wood in a fireplace or burn gasoline in a car's engine. 2.Mechanical Energy is energy stored in objects by tension. Compressed springs and stretched rubber bands are examples of stored mechanical energy. 3.Nuclear Energy is energy stored in the nucleus of an atom — the energy that holds the nucleus together. Very large amounts of energy can be released when the nuclei are combined or split apart. Nuclear power plants split the nuclei of uranium atoms in a process called fission. The sun combines the nuclei of hydrogen atoms in a process called fusion. 4. Electrical Energy is delivered by tiny charged particles called electrons, typically moving through a wire. Kinetic Energy Kinetic energy is motion — of waves, molecules, objects, substances, and objects. • Motion Energy is energy posessed by moving objects. – The faster they move, the more energy they possess. • It takes energy to get an object moving and energy is released when an object slows down. Wind is an example of motion energy. A dramatic example of motion is a car crash, when the car comes to a total stop and releases all its motion energy at once in an uncontrolled instant. Other Forms of Kinetic Energy Kinetic energy is motion — of waves, molecules, objects, substances, and objects. 1. Radiant Energy is electromagnetic energy that travels in transverse waves. Radiant energy includes visible light, x-rays, gamma rays and radio waves. Light is one type of radiant energy. Sunshine is radiant energy, which provides the fuel and warmth that make life on Earth possible. 2.Thermal Energy, or heat, is the vibration and movement of the atoms and molecules within substances. As an object is heated up, its atoms and molecules move and collide faster. Geothermal energy is the thermal energy in the Earth. 3. Sound is the movement of energy through substances in longitudinal (compression/rarefaction) waves. Sound is produced when a force causes an object or substance to vibrate — the energy is transferred through the substance in a wave. Typically, the energy in sound is far less than other forms of energy. HOW WE WILL USE POTENTIAL ENERGY AND KINETIC ENERGY IN OUR STUDIES / GIZMOS / LABS The type of Potential Energy that we will discuss is GRAVITATIONAL POTENTIAL ENERGY- it depends on an object’s mass, the acceleration due to gravity, and the object’s height above the ground. P.E. = mgh P.E. = wh Acceleration due to gravity= 9.8 meters/second2 1 2 KE mv 2 KINETIC ENERGY- is the energy possessed by objects in motion it depends on an object’s mass and it’s velocity These 2 forms of energy are very easily converted to one another. Think of a hawk that goes into a dive to catch prey, or a boulder falling in a landslide. In each case, gravity and height above the ground give the object the POTENTIAL to travel at high velocity. As they fall, and lose height, their potential energy is converted to kinetic energy, as shown by their increasing velocity – they fall faster. The Conservation of Energy 1.The Law of Conservation of Energy states that energy cannot be created or destroyed. 2.Energy can only be transferred from one form to another. 3.The total amount of energy in the universe never changes. 4.Energy is never lost, only transferred. * See the following slides for examples LAWS OF ENERGY Energy Is Neither Created Nor Destroyed but converted from one form to another Energy conversion is not always efficient. Much of the energy is converted to heat and lost as a form of useful energy. The sun produces energy through the process of fusion. Hydrogen atoms fuse together to form helium atoms and this creates a huge amount of radiant energy . The sun is constantly converting its potential energy to kinetic energy through this processs FURTHER USES AND EXAMPLES The most common type of energy is actually a combination of energies. Mechanical energy includes gravitational potential energy, kinetic energy, and heat energy. mechanical energy (ME) – energy due to position and motion; sum of potential and kinetic energies, including friction (heat, air resistance, etc.). ME PE KE heat So, KE = ME – PE and PE = ME - KE Energy is measured in the unit JOULES Joule is equal to a Newton times a meter. A Newton is a measure of weight (force). Newton (Force) = (mass)(acceleration due to gravity) Weight is dependent on gravity: The acceleration on earth due to gravity is 9.8m/s2. Thus potential energy = (mass of object)(9.8m/s2)(height-m) = Joules and Thus kinetic energy = 0.5(mass of object)(velocity2) = kg(m 2/s 2) = Joules http://adventure.howstuffworks.com/roller-coaster3.htm The diagram shows some positions in the path of a pendulum swinging from a fixed point called a fulcrum. The pendulum is raised to the start position and released. At which two numbered positions is the potential energy of the pendulum most likely the same? The diagram represents a diver’s motion from the top of a high diving board into a pool of water. At which point is his potential energy a) the highest? b) The lowest? http://helpmyphysics.co.uk/wordpress/?p=266 http://phet.colorado.edu/simulations/sims.php?sim=Pendulum_Lab http://phet.colorado.edu/simulations/sims.php?sim=Energy_Skate_Park http://phet.colorado.edu/simulations/sims.php?sim=Lunar_Lander