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S Chapter 3 Lesson 1 Energy S The ability of a system to do work. Two types of energy: • Kinetic Energy • Potential Energy States of Energy All forms of energy can be in either of two states: What’s the difference? S Kinetic Energy is the energy of MOTION S Potential Energy is STORED energy. Kinetic Energy – what does it depend on? 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. Kinetic energy depends on both mass and velocity. Calculating Kinetic Energy KE 0.5 mass velocity 2 What has a greater affect of kinetic energy, mass or velocity? Why? What is the unit for Kinetic Energy? S Unit: Joule S Named after: James Prescott Joule S He discovered the relationship between heat (energy) and mechanical work which led to the law of conservation of energy. S How do we derive this unit? S 1 Joule = 1kg ∙ m2/s2 S KE = ½ ∙ m(kg) ∙ v(m/s) 2 Some types of Potential Energy include… Gravitational potential energy - stored energy due to an objects position (height) - depends on mass of the object and its distance from earth. Elastic potential energy - Stored energy due to - Stored energy due to compression or expansion of an elastic object Calculating Potential Energy PE mass gravity height S OR you could multiply weight (in Newton’s) by height What unit do we use for Potential Energy? S Unit: Joule S How do we derive this unit? S 1 Joule = 1kg ∙ m2/s2 S PE = m(kg) ∙ g (m/s2 ) ∙ height (m) 1. You serve a volleyball with a mass of 2.1 kg. The ball leaves your hand with a speed of 30 m/s. The ball has ___________ energy. Calculate it. 2. A baby carriage is sitting at the top of a hill that is 21 m high. The carriage with the baby weighs 12 N. The carriage has ____________ energy. Calculate it. 3. A car is traveling with a velocity of 40 m/s and has a mass of 1120 kg. The car has ___________energy. Calculate it. 4. A cinder block is sitting on a platform 20 m high. It weighs 79 N. The block has _____________ energy. Calculate it. 5. A roller coaster is at the top of a 72 m hill and weighs 966 N. The coaster (at this moment) has ____________ energy. Calculate it. 6. Two objects were lifted by a machine. One object had a mass of 2 kilograms, and was lifted at a speed of 2 m/sec. The other had a mass of 4 kilograms and was lifted at a rate of 3 m/sec. a. Which object had more kinetic energy while it was being lifted? b. Which object had more potential energy when it was lifted to a distance of 10 meters? Show your calculation. As a basketball player throws the ball into the air, various energy conversions take place. Lesson 2 Law of Conservation of Energy S Energy can be neither created nor destroyed by ordinary means. transformed or transferred one form to another. S Energy can be from is the same before and after any transformation or transfer. S The total amount of energy Energy Transfer S Energy TRANSFER is the passing of energy from one object to another object. Example: A cup of hot tea has thermal energy. Some of this thermal energy is transferred to the particles in cold milk, in which you put to make the coffee cooler. Energy Transformation S A change from one form of energy to another. S Single Transformations S Occur when one form of energy into another to get work done. needs to be transformed S Multiple Transformations S Occur when a series of energy transformations are needed to do work Energy Transformation S An objects energy can be: 1. All Kinetic Energy 2. All Potential Energy 3. A combination of both increases and potential energy decreases S As velocity decreases kinetic energy decreases and potential energy increases WHAT IS THE TYPE OF RELATIONSHIP KE AND PE HAVE? INVERSE S As velocity increases kinetic energy Roller Coasters Does energy get transferred or transformed? • As you move up to the first hill on a roller coaster the distance between the coaster and the Earth increases, resulting in an increase of Gravitational Potential Energy. • At the top of the first hill you have the most Gravitational Potential Energy • As you begin your trip down the hill you increase your speed resulting in a transformation from GPE to KE. • At the bottom of the hill right before it goes back upward the GPE is small, but the KE is Large. • As it starts to move up the next hill or loop KE is transformed back into GPE http://www.youtube.com/watch?v=8abzpX CjyjA