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Kinetic and Potential Energy What is Energy? What does it mean if you have a lot of energy? For students it means you can run around, lift weights and scream. If you have energy you can do things. What is Energy? Energy is the ability to do work This is similar to our every day definition of energy. You can’t run up the stairs (work) without energy! We have lots of types of energy. Can you name a few? Definition of Potential Energy… Energy due to position or stored energy. Examples of Potential Energy: Stretching a rubber band… (stored mechanical potential energy) Using uranium for energy… (nuclear potential energy) Yo–Yo in held in your hand… (gravitational potential energy) Lighting a match… (chemical potential energy) Gravitational Potential Energy Gravitational Potential Energy is energy due to an objects height above the ground Things that are positioned higher have greater potential energy Heavier things have greater potential energy. Stored Mechanical Potential Energy Energy that is stored due to being stretched or compressed is called stored mechanical potential energy. A sling shot, bow and arrow and springs all have stored mechanical potential energy. Chemical and Nuclear Potential Energy Chemical and Nuclear energy is energy that is stored in the atoms of elements. When you split an element (nuclear) or combine elements (chemical), a lot of energy is given off. The energy is not given off until it is split or combined, so it is considered to be STORED ENERGY. Definition of Kinetic Energy… The energy of motion. • This includes heat, light, sound, electricity and moving objects. •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. Examples of Kinetic Energy… Shooting a rubber band. Electricity powering a light bulb. Heat waves. Beating a drum. Birds flying. Heat • Heat is made when the particles of a substance moves. The faster the particles move, the more heat energy is created. • Heat moves between objects that are touching (called conduction) and between objects that are not touching (radiation and convection) Electromagnetic Energy • This spectrum includes radio waves, infrared rays, visible light, ultraviolet rays, x-rays and gamma rays. Observe an exploded star at different wavelengths. • Light is part of a spectrum of electromagnetic waves. Light enables people to read, see flowers, determine colors and much more. Sound Everything that moves makes a sound as its particles slide past one another. The sound something makes is a type of energy that can travel toward your ear in the form of sound waves. Once the sound wave hits your ear, your ear drum and inner ear senses the vibrations and sends signals to your brain. Electric Energy Electric energy is associated with an electric charge. Electric charges can be used to do work. Batteries, which convert chemical energy to electrical energy, are used to operate you cell phones and laptops. Electrical energy also happens in nature, as lightning. Motion • The movement of an object from one place to another is considered motion. • Because “kinetic energy” is defined as energy of motion, the faster you move, the more kinetic energy you have. • Motion can be described by calculating speed or acceleration of an object. The Law of Conservation of Energy Energy can’t be created or destroyed. It can only be changed from one form to another. If energy seems to “disappear”, then consider that energy might have been changed to motion, sound, heat or light. Energy conversions All forms of energy can be converted into other forms. The sun’s energy through solar cells can be converted directly into electricity. Green plants convert the sun’s energy (light) into starches and sugars (chemical energy). Potential Energy Converted to Kinetic Energy… Energy is always transferring between potential and kinetic energy. When stored energy begins to move, the object now transfers from potential energy into kinetic energy. Standing still Running What happens when the cord is cut? Potential energy is converted to kinetic energy! Kinetic-Potential Energy Conversion 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. Kinetic vs. Potential Energy At the point of maximum potential energy, the car has minimum kinetic energy. Kinetic and potential energy conversions Describe the energy conversions in this picture: At the top: All PE, no KE ¼ of the way down: 3/4 PE, 1/4 KE ½ way down: 1/2 PE, 1/2 KE ¾ down 1/4 PE, 3/4 KE At the bottom: No PE, All KE Is the sum of KE + PE a constant? Ball slows down Ball speeds up The End...