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Energy Energy is the ability to do work Massless and does not take up space It can be measured only by its effects on matter Comes in many forms such as energy of motion, stored (potential) energy, chemical energy, or energy associated with nuclear forces Energy is defined as the ability to do work or to put matter into motion. Sometimes that motion is microscopic, resulting in heat, and other times it is macroscopic. It can be obvious, like the energy associated with a moving car, or hidden, such as that stored in a stretched rubber band or a rock high on a mountain. NASA Image from http://www.nasa.gov/audience/forstudents/k-4/dictionary/Energy.html
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HEAT AND ENERGY
TRANSFER
Images from Microsoft Office Clipart
ENERGY• Energy is the ability to do work
• Massless and does not take up space
• It can be measured only by its effects on matter
• Comes in many forms such as energy of motion, stored (potential) energy, chemical energy, or energy associated with nuclear forces
NASA Image from http://www.nasa.gov/audience/forstudents/k-4/dictionary/Energy.html
HEAT• Heat is transferred energy that arises
from the random motion of molecules
• The ability to transfer and store heat is related to the structure of a substance
• Heat transfer involves at least one substance losing energy and another gaining energy
NASA Image from http://science.hq.nasa.gov/kids/imagers/ems/infrared.html
Transfer of Energy through Heat• Conduction (solids)
• Convection (fluids – gases and liquids)
• Radiation (light, heat, radio waves - can pass through a vacuum)
NASA images from http://spaceplace.nasa.gov/review/beat-the-heat/
Conduction
• Transfer of heat within and between substances that are in direct contact with each other
• The better the conductor, the more rapid the heat transfer
Images from Microsoft Office Clipart
Convection• Convection is the transfer of heat by the bulk motion of the
substance containing the heat.• Natural convection happens
when warm (less dense) substances rise– Natural convection plays a roll in
plate tectonics, global wind and ocean currents.
• Forced convection is a result of moving the substance intentionally, such as with a fan– heating systems and computer
cooling fans are examples of forced convection
Image from NASA: http://www.virtualskies.arc.nasa.gov/weather/3.htmlImage from EPA: http://www.energystar.gov/index.cfm?c=business.EPA_BUM_CH8_AirDistSystems
Electromagnetic Energy - Radiation
Wikimedia Commons from NASA
KEY TERMS• Energy – ability to do work• Heat – Heat is transferred energy that arises
from the random motion of molecules• Temperature – a relative term reflecting how
vigorously the atoms of a substance are moving and colliding.
UNITS OF HEAT• Calorie– The amount of heat required to raise the temperature
of one gram of water 1oC. • BTU (British Thermal Unit)– The amount of energy needed to heat one pound of
water one degree Fahrenheit• Joule– The international unit of energy, not defined by a
temperature change– 4.184 Joules in one calorie– 1,054.35 Joules in one BTU
Cooling a Hot Glass of Liquid
Thermos
• In the winter homes lose heat to the outside through conduction, convection, radiation, and infiltration
• These losses can be reduced by good home design, but there is always some loss of heat
• To keep the inside of a home warm the lost heat needs to be replaced
Heating Losses in a Home
Image from energy.gov: http://energy.gov/public-services/homes
