Transcript Energy
and Work What is energy? •Ability to make something happen •Or work to happen Potential and Kinetic Energy • Potential energy is energy that is stored in an object. • Kinetic energy is energy of motion. Potential energy • Potential energy (P.E.) is the ability of an object to do work because of its position. work done by the object = P.E. lost • work done on the object = P.E. gained. Potential energy • Potential energy is a type of energy that is "hidden" in some way. It is a type of energy that can be converted to other forms and often is related to some attractive or pushing forces. Types • Elastic Potential Energy – Anything that can act like a spring or a rubber band can have elastic potential energy. – Let's take the rubber band or a spring – Wind up toys store energy this way Gravitational Potential Energy • There is a constant attractive force between the Earth and everything surrounding it, due to gravity. • To lift something off the ground it takes energy, so just by lifting an object, that object now has higher gravitational potential energy. • Gravitational potential energy is typically converted into kinetic energy (an object falling) before it is converted into any other type of energy. • Hydroelectric power is generated this way. As the water falls, it turns a turbine, which pushes electrons around, creating an Changing GPE • What does it depend on? Chemical Potential Energy • A chemical bond can be thought of as an attractive force between atoms. • Because of this, atoms and molecules can have chemical potential energy. • Anytime two atoms form a strong covalent or ionic bond or two molecules form a chemical energy is converted into other forms of energy, usually in the form of heat and light. • Strong bonds have low chemical energy and weak bonds have high chemical energy. Kinetic energy is the energy of motion. • Any object that is moving has kinetic energy. • Ball Moving Horizontally • Kinetic Energy Equation • m = mass (in kg), v = velocity (in m/s), and KE = kinetic energy (in J = joules). • Remember, the units for energy are Joules - Kilogram . meters / sec2 • Practice Problems: • 1. A 12 pound bowling ball is held 20 feet above the floor. Calculate its GPE. • 2. A 2kg object is traveling at 4m/s. Calculate its KE. • Law of Conservation of Matter and Energy: the total matter and energy in the universe is always conserved. Can energy be changed into matter? • Think of matter and energy as two forms of the same thing that can be converted from one to another. E=mc2 • While it is possible to change matter into energy and energy into matter, the sum of the two is always constant. • Einstein's equation shows this relationship. • E = Energy (Joules) • m = mass (kg) • c = speed of light (300,000 km/s) • The two most common energy conversions are: • Potential energy changing into kinetic energy. • Kinetic energy changing into potential energy • Mechanical energy= potential energy + kinetic energy • Mechanical is energy due to the motion of an object Mechanical energy Forms of energy • Mechanical • Chemical • Heat • Electromagnetic • nuclear Mechanical energy • There are two main types of mechanical energy. • Motion energy: This is the energy something has because it is moving • Stored mechanical energy: This is energy something has stored in it because of its height above the ground or because it is stretched or bent or squeezed Electrical energy • The energy that flows through wires and powers the lights and appliances in your home. • The energy is in the form of moving electrons Electromagnetic energy • Visible light or radiant energy • X rays • Radio waves • Microwaves • This form of energy can travel through a vacuum • Concept Understanding: • • 1. Assume that all the matter in your body could be converted into energy, how many Joules of energy would that be? • Hint: 1 pound = 0.5 kg • Show all your work used to solve this problem. • 2. Give one example of each of the following energy conversions: • Chemical energy changing into heat energy. • Heat energy changing into mechanical energy. • Nuclear energy changing into heat energy. • Mechanical energy changing into electromagnetic energy. Conservation • Matter can be changed into energy • Energy can be changed into matter • Neither can be created or destroyed Work • Develop a definition from the activity Work • W=force x distance • W=fxd • The unit is the newton/meter also called joule • Work is force exerted through a distance • Complete activity pg 303 Measure work • To measure work you must measure the force in the direction of motion • Complete problems #3, 7, and 8 on page 303 Power • Power=work/time • It is a rate • The unit is the watt---W or 1 j/s Analysis and conclusion • 1 When the mass is released from the same height with the interrupter, is the ending height the same as its starting height? Use your data to support • 2 Analyze the energy transfers. At what point along a single swing does the mass have the greatest kinetic energy? The greatest potential energy • 3 Do the results support your hypothesis? • 4 Compare the starting heights to the ending heights of the mass. Is there a pattern? Can you account for the observed behavior? • 5 Do your results support the law of conservation of energy? Why or why not? • 6 What would happen if the mass of the bob was increased?