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2B_2_2: Heat Energy

2B_2_2: Heat Energy. Types of Energy:. Mechanical Energy = KE + PE Kinetic Energy [KE] is associated with MOTION [speed]. Potential Energy [PE] is associated with position [height, separation]. Gravitational PE : Separation of masses. Masses attract [pull on] one another.

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2B_2_2: Heat Energy

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  1. 2B_2_2: Heat Energy

  2. Types of Energy: • Mechanical Energy = KE + PE • Kinetic Energy [KE] is associated with MOTION [speed]. • Potential Energy [PE] is associated with position [height, separation]. • Gravitational PE: Separation of masses.Masses attract [pull on] one another. • Electric PE: Separation of charges.Opposites attract [pull]; Similar repel [push]. • Chemical PE: Separation of atoms within molecules.

  3. Heat Energy • Heat Energy is associated with the vibration of atoms and molecules. Heat is proportional to the TOTAL KE of the particles. • Temperature is also associated with the vibration of atoms and molecules. Temperature, in Kelvin [not Celsius or Fahrenheit], is proportional to the AVERAGE KE of the particles. • Here’s the difference: one drop of boiling water versus one gallon of boiling water … spilled on your hand. Same temperature, different heat energies!

  4. Heat Energy • Heat Energy flows from high T to low T. • Cold does not exist. Cold is the absence of heat.

  5. Definitions: • System: What you are looking at. • Surroundings: What is around the system. • Universe = System + Surroundings. • Closed System: No mass enters or leaves.[Open System: Mass can enter or leave.] • Isolated System: No energy enters or leaves.[Non-isolated: energy can enter or leave.]

  6. Energy is conserved. Always. • An isolated system is insulated from its surroundings. Remember, the system + surroundings = universe. • No heat flows into or out of the system because the system is insulated. • Energy of an isolated system does not change. • Energy of the surroundings doesn’t change. • Energy of the universe doesn’t change. • Think hot chocolate in a double Styrofoam cup! Heat doesn’t flow to your hand.

  7. Energy is conserved. Always. • A non-isolated system isn’t insulated at all. Or isn’t insulated very well. • If the system is not insulated, energy will flow between the system and the surroundings, from HIGH T to low T. • If the system is at a higher T than the surroundings: • The system will lose heat energy. • The surroundings will gain heat energy. • The energy of the universe won’t change! • Think hot cocoa in a metal cup without a handle. Energy lost by the cocoa is gained by your hand. Quickly. Ouch.

  8. Energy is conserved. Always. • Most systems are between the two extremes, neither uninsulated nor perfectly insulated. • Heat Energy flows, but it flows slowly. • Even a Styrofoam cup allows the slow transfer of energy.

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