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Ch 15 and 16. Energy and Heat. Energy is the ability of an object to cause change Basic unit is the Joule (J) =Nm. Forms of energy 1. Mechanical = PE+KE 2. Thermal = heat 3. Chemical = wood, gasoline 4. Electrical = lightning, batteries 5. Electromagnetic = visible light, x-rays
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Ch 15 and 16 Energy and Heat
Energy is the ability of an object to cause change • Basic unit is the Joule (J) =Nm
Forms of energy 1. Mechanical = PE+KE 2. Thermal = heat 3. Chemical = wood, gasoline 4. Electrical = lightning, batteries 5. Electromagnetic = visible light, x-rays 6. Nuclear = fission, fusion
Kinetic Energy – energy in the form of motion • a. Greater mass, more KE • b. Greater velocity, more KE
A 20-kg kid slides down a slide at a velocity of 2 m/s. What is the kinetic energy of the kid?
Potential Energy – stored energy a. Amount depends on: 1. Position 2. Shape
Types of PE: 1. Gravitational – related to height above Earth’s surface a. Higher up, more PE b. Greater mass, more PE
PE h mg • PE=mgh=Fgh • SI unit is Joule=J=Nm
A potted plant on a 2.5 m high window sill has a mass of 3-kg. What is the potential energy of the plant?
A man weighing 950N stands at the top of 30m cliff. What is the man’s potential energy?
3 people of equal mass climb the mt using different paths. Which path shows the person gaining the most PE?
Roller coaster max height PE speed ME
Energy Conversion – process of changing energy from one form to another
Law of Conservation of Energy states that matter cannot be created nor destroyed
STAR Questions • List the 6 forms of energy • Mechanical, chemical, electromagnetic, thermal, electrical, nuclear • Work depends on what 2 things? • Distance and force • KE, chemical PE, elastic PE or gravitational PE? • Bouncing ball • Rock at edge of cliff • Glass of Orange Juice • Car battery • Compressed spring KE Gravitational PE Chemical PE Chemical PE Elastic PE
30oC 90oC Ch 16-HEAT Heat =energy that flows from higher temps to lower temps What will happen to the temperature in the beakers over time?
Temperature –measure of average KE of the particle in a sample of matter • a. Increase temp = greater KE • b. Decrease temp = lower KE • c. Absolute Zero=0K= KE of all particles cease
Thermal Energy – the total energy of the particles in a material (both KE and PE) a. More mass at the same temp means greater thermal energy
KE of 3? TE of 3? 50oC 70oC 70oC 200g 400g 200g
Thermal Expansion & Contraction a. Hot temps cause materials to expand b. Cold temps cause materials to contract
Specific Heat (C) – amount of energy needed to raise the temp of 1g of a material by 1oC • Think of it as “resistance to temperature change” • The higher the c, the harder it is the change the temp.
An iron spoon and a silver spoon have the same mass. Which becomes hotter when both are left in hot chocolate for one minute? Pg 476 for c values
Why does a piece of steel heat up more than an equal mass of wood when both absorb the same energy? The metal has a lower specific heat than the wood, so its temp increases more as thermal energy is absorbed
Which substance will have the greatest increase in temp when equal masses absorb equal amounts of thermal energy? • Water (4.18 J/goC) • Ethyl alcohol (2.43 J/goC ) • Ammonia gas (2.1 J/goC ) • Aluminum (0.90 J/goC ) • Lead (0.46 J/goC )
The same energy was added to each sample. Which material has the highest specific heat? Al, b/c Temp rises the least for a given amt energy added. Smaller ΔT means a larger specific heat
Conduction – transfer of energy through matter by direct contact of particles a. Energy is transferred when particles moving at different speeds collide b. Occurs in solids, liquids, and gases • 1. Solids conduct better
Convection – transfer of energy by the movement of matter a. Fluid – anything that flows b. Occurs in liquids & gases
Radiation –transfer of energy in form of waves a. Shiny materials reflect radiant energy b. Dull materials absorb c. Darker colors absorb more d. Lighter colors absorb less
STAR Questions • Decrease temperatures = ___________ KE • Decreased • Hot temperatures cause materials to ______ • Expand • The higher the C-specific heat, the _________ it is to change the temp • Harder • Dull materials ___________ radiant energy • Absorb • Lighter colors reflect ___________ radiant energy • less