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CH 4 Energy I. Energy and Types A. Energy – ability to do work or cause change B. 5 general types of energy 1. mechanical – any movement 2. electromagnetic – light, radio waves, etc. (CH 13) 3. chemical – potential energy stored in chem.. bonds ex) food, gasoline 4. thermal – heat 5. nuclear – stars + nuclear reactions C. Types of mechanical energy 1. Kinetic Energy (KE) – energy of moving objects a. formula: KE = ½ m x v2 ( m = mass, v = speed) b. units – Joules (J) ex) Find the KE of a 100 kg person running at 4 m/s. KE = ½ x 100 x 42 KE = ½ x 100 x 16 = 800 J 2. Gravitational Potential Energy (GPE) – energy stored due to position a. formula: GPE = m x g x h ( h = height) b. units: joules ex) Find the gravitational potential energy of a 10 kg rock that is 5 meters above the ground on a cliff. GPE = 10 x 9.8 x 5 = 490 J c. higher object more PE 3. Elastic Potential Energy (EPE) – energy stored in a stretchy object ex) spring and rubber band a. formula: EPE = ½ kx2 1) k – spring constant tells how much force is made for each unit of distance of stretch or compression 2) x – how far spring is stretched or compressed from normal length II. Conservation of Energy A. Law of conservation of energy - energy can neither be created nor destroyed, but can change forms ex) digested food turns chemical energy into body heat and movement 1. if bouncing ball did not convert KE to sound and heat, it would bounce forever at same height B. Falling Objects – GPE turns to KE as falling object moves faster 1. projectile - thrown object loses KE when rising, then regains as falls a. if lands at same height as thrown, will have same KE upon landing as when first thrown b. diagram 1) position A and E, KE max, GPE = zero 2) position B: KE decreasing, GPE increasing 3) position C: KE min., GPE max 4) position D: KE increasing, GPE decreasing C. Pendulum – pg 110 – swinging objects (diagram side) 1. position A, E: max GPE, zero KE 2. position B: inc. KE, dec. GPE 3. Position C: Max KE, zero GPE 4. position D: inc. GPE, dec. KE D. Mass/Energy Conversions – Einstein – mass traveling at speed of light changes into energy 1. Formula E = m x c2 (E = energy, c = speed of light) 2. Conversion methods: a. Fission – splitting atoms – nuclear power plants and bombs 1) starting atom split into 2 nearly equal sized atoms, but some mass turns into energy b. Fusion – small atoms combining to make bigger ones – sun and bombs 1) in sun, 2 hydrogens form one helium and some mass turns to energy 2) biggest atoms most stars can make is oxygen 3) bigger atoms formed in supernovas or big bang