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Section 4.1 - The Nature of Energy

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Warm-Up: Examine your lab data from yesterday. What relationship do you notice between momentum and kinetic energy? Can you think about why this might be true? Learning Goal(s): Compare and contrast kinetic energy and momentum. Agenda: - 1.Warm-Up 2.Work on Analysis and Conclusions for the Kinetic Energy Lab 3.Complete the Kinetic Energy and Potential Energy Problem Set Kinetic Energy and Potential Energy Problem Set (1 st side only) due on Tuesday, 12/3HW: Kinetic Energy and Potential Energy Problem Set (1 st side only) due on Tuesday, 12/3 Have a Happy Thanksgiving!

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Kinetic Energy vs. Momentum

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What Is Energy? Changes are constantly occurring in the world. – Examples: light bulbs heating the air, sunlight on window, you breathing Every change requires energy. Energy – ability to cause change

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Energy is Found in Many Forms Electromagnetic energy – energy in waves – Examples: UV, Infrared, Radio Mechanical – energy in physical movement – Examples: moving car, flying baseball Electrical energy – energy carried by moving electrons Heat – thermal energy – Example: cup of hot tea Chemical – stored in molecules – Example: food, batteries Nuclear – energy stored in the nucleus of an atom – Example: Uranium used in nuclear reactors Kinetic – energy an object in motion has – Example: person running, roller coaster going down a hill Potential – stored energy due to an object’s position – Example: roller coaster at the top of a hill

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Units of Energy – the Joule Units of energy kg x m 2 /s 2 Abbreviated J James Prescott Joule

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Kinetic Energy Energy a moving object has because of its motion. Depends on an object’s mass and its speed. KE = ½ mv 2 KE – kinetic energy in Joules (J) m – mass in kg v – velocity (m/s)

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Examples of Solving for Kinetic Energy A jogger with a mass of 60 kg is moving at a speed of 3 m/s. What is the kinetic energy? A bowling ball is moving with 300 J of energy. The ball weighs 2 kg. How fast is the ball moving?

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Potential Energy Stored energy due to an object’s position Three types: – Elastic potential energy – energy stored by something that can stretch or compress – Chemical potential energy – energy stored in chemical bonds – Gravitational potential energy – energy stored in objects due to their position above the Earth’s surface

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Solving for Potential Energy GPE = mgh GPE – gravitational potential energy (in J) m – mass (in kg) g – 9.8 m/s 2 h – height (in m)

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Examples of Solving for Potential Energy What is the gravitational potential energy of a ceiling fan that has a mass of 7 kg and is 4 m above the ground? How high above the ground is a baseball with a mass of 0.15 kg and a GPE of 73.5 J?

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Changing GPE As an object begins to fall it has GPE and KE. As the object gets closer to the ground it has less GPE and more KE. Example – An 80 kg skydiver jumps from a 10 m platform. What is the GPE of the skydiver at the top of the platform? What is the GPE of skydiver after falling 5 m?

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Changing GPE – Energy Diagram

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