Transcript energy
BELLWORK 9/8/15 What are your goals for after graduation? **Give me 4 sentences minimum** FIND YOUR NEW SEATS AND BE IN THEM, PLEASE! Chapter 15.1 Energy Learning Objectives Section 15.1 Describe the relationship between work and energy Relate kinetic energy to the mass and speed and calculate these quantities Analyze how potential energy is related to an object’s position and give examples of gravitational and elastic potential energy. Solve Equation that relate an object’s gravitational potential energy to its mass and height. Give examples of major forms of energy and explain how each is produced. Energy and its forms In an avalanche, a mass of loose snow, soil, or rock suddenly gives way and slides down the side of a mountain. The avalanche releases a great amount of energy. How are work and energy related? Energy is the ability to do work Work is the transfer of energy Work and energy are closely related. • Energy is known by the changes it causes. • Work is done when a force moves an object through a distance. Energy is transferred by a force moving an object through a distance. • Both work and energy are typically measured in joules (J). Energy has different forms A. The sun gives off energy in the form of heat and light. B. Plants convert sunlight into food. C. People convert food energy into muscle movement. What is Kinetic Energy? Energy of Motion. What factors does Kinetic Energy depend on? Mass Speed Kinetic Energy Doubling the mass in the formula doubles the kinetic energy. Doubling the speed quadruples the kinetic energy. Formula: 80 km/hr 50 km/hr 80 km/hr Who has more kinetic Energy? Who has the least? Which has the most KE? 80 km/hr truck Which has the least KE? 50 km/hr motorcycle Practice Problems Kinetic Energy A 0.10 kilogram bird is flying at a constant speed of 8.0 m/s. What is the bird’s kinetic energy? Step1Givens Mass = 0.10kg Speed = 8.0m / s KE = ? Step3Answer Step2Formula KE=1/ 2mv KE=1/ 2mv2 2 KE =1/ 2·0.10kg·(8.0m / s)2 KE =1/ 2·0.10kg·(8.0m / s) 3.2kg·m2 / s2 = 3.2J 2 What is Potential Energy? Potential energy is energy that is stored as a result of position or shape. Gravitational Potential Energy Energy stored in position So what does gravitational potential energy depend upon? (PEg) Mass Height Acceleration due to gravity - The potential energy increases when an object is raised to a higher level Gravitational Potential Energy PEg The unit for mass is kilograms. The unit for height is meters. Acceleration due to gravity, g, has a value in SI units of 9.8 m/s2 on Earth. The unit for gravitational potential energy is joules. Formula: More on Potential Energy Height is measured from the ground or floor or some other reference level. Doubling either the mass of the object or its height doubles its gravitational potential energy. Examples of Gravitational Potential Energy This diver has gravitational potential energy as she stands at the end of a diving board. She gained the potential energy by doing work—by climbing up the steps to the diving board. Practice Problems - PEg What is the potential energy relative to the water surface of a diver at the top of a 10.0 – meter high diving platform. Suppose she has a mass of 50.0 kilograms. Step1- Givens Height = 10.0m Mass = 50.0kg PEg = ? Step3- Answer Step2-Formula PEg = mgh PEg = mgh PEg =50.0kg·9.8m/s ·10.0m PEg = 50.0kg·9.8m / s ·10.0m 2 2 PEg = 4900kg·m / s2 = 4900J Elastic Potential Energy The potential energy of an object that is stretched or compressed is known as elastic potential energy. Something that is elastic springs back to its original shape after it is stretched or compressed. Major Forms Energy The ability to cause change. THERMAL internal motion of particles NUCLEAR MECHANICAL ENERGY changes in the nucleus ELECTROMAGNETIC ELECTRICAL CHEMICAL bonding of atoms motion of objects joules (J) motion of electric charges Mechanical Energy The energy associated with the motion and position of everyday objects is mechanical energy. Mechanical energy is the sum of an object’s potential energy and kinetic energy. Thermal Energy The total potential and kinetic energy of all the microscopic particles in an object make up its thermal energy. When an object’s atoms move faster, its thermal energy increases, and the object becomes warmer. Increasing the temperature – increases the thermal energy Molten metals contains great deal of thermal energy Chemical Energy Chemical energy is the energy stored in chemical bonds. When bonds are broken or formed; the released energy can do work. All chemical compounds, including fuels such as coal and gasoline, store energy. Burning wood – is a combustion reaction which breaks bonds thus producing thermal energy Electrical Energy Electrical energy is the energy associated with electric charges. Electric charges can exert forces that do work. Electromagnetic Energy Electromagnetic energy is a form of energy that travels through space in the form of waves. Visible light and X-rays are examples of electromagnetic energy. A. Lightning bolts transfer electric charge. B. Galaxies are giant structures in space that typically contain billions of stars. The stars give off enormous amounts of electromagnetic energy. Nuclear Energy The nucleus of an atom is held together by strong and weak nuclear forces, which can store an enormous amount of potential energy. • The energy stored in atomic nuclei is known as nuclear energy. • Nuclear fission releases energy by splitting nuclei apart. • Nuclear fusion releases energy when less massive nuclei combine to form a more massive nucleus.