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Published byDarrell Pope Modified over 6 years ago

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Energy ENERGY

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Energy Defined Energy is the ability of an object to produce a change in itself or the environment.

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Energy Transfer Work is done when energy is transferred from one form of energy to another.

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The Units for Measuring Energy Are the same as the units for measuring WORK JOULEs in the SI system FOOT-POUNDS in the British System

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TYPES OF ENERGY

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Mechanical Energy Energy is the ability to do work

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Mechanical Energy(ME) - enables an object to do work A. Kinetic Energy (E k ) - energy of motion B. Potential Energy(E p ) - stored energy

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Gravitational Potential Energy An object lifted against the force of gravity has stored energy. UNIT= JOULE

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Gravitational Potential Energy Only changes in potential energy can be measured E p = mgh m= massg= gravityh= height

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As an object, such as a boulder, begins to move, it gains velocity. Gaining velocity increases the object’s kinetic energy.

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Example Problem Legend has it that Isaac Newton “discovered” gravity when an apple fell from a tree and hit him in the head. If a 0.20 kg apple fell 7.0 m before hitting Newton, what was its change in E p during the fall?

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Kinetic Energy Unit: Joules

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Kinetic Energy Examples Pitched baseball 150 J (148 g @45 m/s) Football linebacker 4500 J (110 kg @ 9.0 m/s)

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Example Problem A greyhound at a race track can run at a speed of 16.0 m/s. What is the KE of the 20.0 kg greyhound as it crosses the finish line?

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Work Work is the transfer of energy from one object to another, or... The change in KINETIC ENERGY!

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E k and E p are constantly changing.

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Law of Conservation of Energy Energy cannot be created or destroyed. ENERGY is merely transformed.

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APPARENT LOSS OF ENERGY FRICTION WASTES ENERGY BY CHANGING USEFUL ENERGY INTO HEAT

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Total Energy At any point, the total energy of an object E t = E k + E p + HEAT

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Potential Energy to Kinetic Energy

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Law of Conservation of Energy

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ELASTIC POTENTIAL ENERGY

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Elastic Potential Energy Sling shots Trampolines Rubber bands Rubber balls

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A Jack in the box has stored energy in a compressed spring.

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k = force to stretch divided by distance stretched The Elastic Constant

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ELASTIC POTENTIAL ENERGY E EP = 1/2 kd 2

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Elastic Potential Energy If a spring of stiffness constant (k) is stretched an amount (d), the elastic potential energy stored in the spring is equal to 1/2 the the spring constant times the square of the distance stretched.

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An automobile stores chemical energy in the gasoline.

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Thermal Energy The total energy of vibrating atoms and molecules that make up a substance. Temperature is the average KINETIC ENERGY of a substance.

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