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Chapter 4 Energy Energy 4-1: The Nature of Energy • When something is able to change its environment or itself, it has energy. Energy • energy – the ability to cause change or the ability to do work • Types of Energy • kinetic energy – energy in the form of motion – the amount of kinetic energy that an object has depends on its mass and velocity – the greater the mass and the greater the velocity the more its energy – kinetic energy is measure in Joule (J) Kinetic Energy Energy • energy – the ability to cause change or the ability to do work – equation: m = mass & v = velocity 1 2 KE = m v 2 Energy 1 2 KE = m v 2 • If a truck is moving at a velocity of 30 m/s and has a mass of 500 kg, what is its kinetic energy? Energy • energy – the ability to cause change or the ability to do work • Types of Energy • potential energy – energy that is stored and based on an objects position – potential energy can be converted to kinetic energy when something acts to release it • example: a book sitting on a shelf has potential energy but when it falls that potential energy is converted into kinetic energy Energy • Potential vs. Kinetic Energy Energy • potential energy – energy that is stored and based on an objects position • Types of Potential Energy – elastic potential energy is stored by something that can stretch or compress • examples: rubber band, spring, or shocks Energy • potential energy – energy that is stored and based on an objects position • Types of Potential Energy – chemical potential energy is energy that is stored in chemical bonds • examples: food that we eat, gasoline Energy • potential energy – energy that is stored and based on an objects position • Types of Potential Energy – gravitational potential energy (GPE) is energy that is stored by objects that are above the Earth’s surface • examples: an apple falling from a tree, a skydiver jumping out of an airplane Energy • gravitational potential energy (GPE) is energy that is stored by objects that are above the Earth’s surface GPE = m g h – m = mass (kg) – g = acceleration due to gravity (9.8 m/s2) – h = height (m) Energy GPE = m g h • A 2 kg ball is dropped on Mr. Thomsen’s head from a height of 10 m. Before it was dropped, how much gravitational potential energy did the ball have? Energy • Relationship Between Kinetic & Potential Energy – As an object drops, potential energy decreases but kinetic energy increases – Since an object is moving while it is dropping, it is gaining kinetic energy – Since an object is no longer at a higher elevation, it is losing potential energy Energy • Potential vs. Kinetic Energy Conservation of Energy • Energy is constantly being transformed from one form to another. For example, a light bulb is transforming electrical energy into light energy, or a car engine transforms chemical energy stored in gasoline into kinetic energy. Conservation of Energy • mechanical energy – the total amount of potential and kinetic energy in a system • Mechanical Energy = Potential Energy + Kinetic Energy – involves both position and motion of an object – the total mechanical energy stays constant while an object falls because potential energy decreases but kinetic energy increases Conservation of Energy • Mechanical Energy Conservation of Energy • Law of Conservation of Energy – energy cannot be created or destroyed only transferred from one form to another – this law implies that the amount of energy in the universe remains constant Conservation of Energy • Law of Conservation of Energy – energy cannot be created or destroyed only transferred from one form to another – example: If you are on a swing and stop pumping your legs, you will eventually come to a stop. So, the swing will then have NO kinetic energy. Where does the energy go? • The swing’s ropes rub on their hooks and some of the energy turns into thermal energy (heat). Air resistance can cause an increase in air temperature. Conservation of Energy • Law of Conservation of Energy – energy cannot be created or destroyed only transferred from one form to another – The swing’s ropes rub on their hooks and some of the energy turns into thermal energy (heat). Air resistance can cause an increase in air temperature. – Energy Lost = Energy Gained