Heat and Heat Transfer

  1. Temperature, Thermal Energy and Heat
  2. Determining the Temperature of an Object
  3. Temperature- the measure of how hot or cold something is compared to a reference point such as the freezing point of water.
  4. How hot or cold something is depends on the kinetic energy (energy of motion) of the particles that make the object.
  5. The faster the motion of particles the higher the kinetic energy.
  6. The faster the motion of the particles the warmer the material gets and vice versa

**Temperature is the measure of the average kinetic energy of the particles in an object

  1. Measuring Temperature
  2. Faherenheit scale (F)- Used by USA
  3. Celcius scale(C)- Used by most other countries and the scientific community
  4. Kelvin scale (K) -Used by the science community
  5. Absolute zero = 0 kelvins is the lowest temperature possible
  6. Particles have no motion and no kinetic energy at all.
  7. 0 K= -273°
  1. Thermal Energy
  2. Temperature only measures the average kinetic energy of an object NOT THE TOTAL ENERGY OF ALL THE PARTICLES IN AN OBJECT.
  3. The total energy of an object depends on
  4. Temperature of object
  5. Arrangement of particles
  6. Number of particles
  7. The more particles an object has at a given temperature, the more kinetic energy that object has.
  8. EX A 24oz. hot chocolate from Starbucks at 75°C has more kinetic energy than a 16 oz. cup of hot choc--simply because there are moe particles in the larger cup.
  1. EX if there were two 24 oz. cups of hot choc and one had a higher temperature than the other, the one with the higher temperature would have higher kinetic energy.
  1. Heat is the transfer of thermal energy from a warmer object to a cooler object.
  2. This makes the warmer object cool down and the cooler object warm

up until they are the same temperature.

  1. Heat stops transferring at this point
  1. Heat is measured in units of energy of “joules” (j).
  1. Transfer of Heat
  2. Heat moves in one direction only and by 3 different methods
  3. Radiation-the transfer of thermal energy by electromagnetic waves.
  1. The only form of heat transfer that does not require matter
  2. This means that heat can be transferred without direct contact.
  3. Sunburn happens because of radiation.
  1. Conduction-
  2. The transfer of thermal energy through direct contact
  3. Happens from warm particle to cool particle between 2 or more objects.
  4. Convection-
  5. The transfer of thermal energy through a fluid like a liquid or the air.
  6. Relies on the differences in temperature.
  7. Heat circulates in convection currents.
  8. As particles heat they gain energy--move faster & spread out
  9. This causes the particles to lose density
  10. Particles float/move up b/c they are less dense.
  11. Once away from the heat source, the particles slow down and move toward each other.
  12. They gain density & sink
  13. Process Repeats over and over again.
  1. Thermal Properties

a- How well a material conducts heat

  1. Conductors- materials that conduct heat well.
  2. Heat transfers into them easily-- metal heats up quicker than wood or plastic
  3. Heat transfers out of them easily--
  4. a tile floor feels cool to the touch because heat transfers out of that material quickly.
  5. A metal seat belt feels very hot in the summer because heat transfers from it to your hand easily.
  6. Most metals -- silver, gold,
  7. Insulators- materials that do not conduct heat well.
  8. Heat does not transfer into them easily or out of them easily
  9. Wool blankets slow the transfer of heat out of your body--making you feel warm.
  10. Styrofoam insulation in a cooler--slows the transfer of heat from the outside air into the cooler--keeping the drinks or sandwiches cool.
  1. Specific Heat
  2. The amount of energy it takes to raise the temperature 1 kg of material one kelvin
  3. Different amounts for different objects because of the matter the object is made out of.
  4. High specific heat allows an object to absorb lots of thermal energy without a large change in temperature
  5. Low specific heat allows an object to change temperature quickly without absorbing much thermal energy.
  6. Calculate energy change:
  7. Thermal Expansion--true of most matter but water. **Water expands when it freezes.
  1. As an object heats, its particles spread out causing the object to expand.
  2. As an object cools, its particles slow down, condense--causing the object to contract.
  3. This is because thermal energy is released as the object cools.