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Chapter 4 Energy What is energy? Def: ability to cause change Every change involves energy Different Forms Electrical Chemical – stored in food, involved in reactions Radiant – gives off Thermal – heat Same thing just different forms Kinetic Energy Def: energy of a moving object Depends on mass and speed Kinetic energy (Joules) = 1 mass (kg) x [speed (m/s)]2 2 KE = 1 mv2 2 SI unit for energy is joule (J) Practice! What is the kinetic energy of a .15 kg baseball moving at 40 m/s. A car moving at a speed of 20 m/s has a kinetic energy of 300,000 J. What is the car’s mass? Potential Energy Even motionless objects have energy Stored in the object, has potential to change Def: stored energy Elastic Potential Energy Def: stored energy by something that can stretch or compress Stretched rubber band – elastic potential energy kinetic energy Chemical Potential Energy Def: energy stored in chemical bonds Food, gasoline, etc. Gravitational Potential Energy Def: stored energy by objects due to position above earth (able to fall) Practice! Find the height of a .15 kg baseball that has a GPE of 73.5 J. Find the GPE of a .3 kg coffee mug on a 1-m high counter. What could you do to change GPE? Change height or mass Section 2 Conservation of Energy Changing Forms of Energy Changing electrical energy – electricity – light and heat energy Energy is constantly changing forms Transforming Chemical Energy Cars – MANY energy transformations Spark plug – gasoline – engine - wheels Transforming Chemical Energy Green plants – take in sunlight and transform to chemical energy in plants Mechanical Energy Def: total amount of potential and kinetic energy Mechanical Energy = Potential + Kinetic Falling Objects As potential kinetic mechanical energy stays same Potential lost = kinetic gained Projectile Motion Mechanical energy remains constant Still see transformations of energy Swinging Best part is falling from highest point High GPE = Low KE Describe transition… Law of Conservation of Energy Def: energy can not be created or destroyed Energy just changes form All energy in the universe does not change Energy in = Energy out Is energy always conserved? Swinging – you eventually will stop – where does all the energy go? Friction – air resistance = thermal energy Human Body – Energy Relations What forms of energy are in your body? Conservation of energy still true Food, fat = potential energy Activity = kinetic energy Calorie 1C = 4,184 J Chapter 6 Section 1 Temperature and Heat Matter in Motion Matter is made of tiny particles in constant motion have kinetic energy Faster = more kinetic energy Temperature Def: measure of average kinetic energy of particles High Temp. = High Energy Low Temp. = Low Energy Unit Kelvin Thermal Energy Collisions between air and butter particles increase energy of butter = higher temperature Def: sum of kinetic and potential energy of particles in object Thermal Energy As temp increases = thermal energy increases If object has MORE MASS and at the same temp. has HIGHER thermal energy Heat Is your seat toasty? Def: thermal energy that flows from something at a higher temp to a lower temp Unit: Joule Beachin’ it up! How can there be extreme differences in temperature from air, sand and water? Sun rays are the same why different temp? Sand heats up 6 times faster than water Specific Heat Specific Heat: heat needed to raise 1kg of material by 1C Water as a Coolant It’s high specific heat – absorb a lot of heat without changing temp much Strong bonds have to be broken before particles move really fast