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Thermal Energy.

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Presentation on theme: "Thermal Energy."— Presentation transcript:

1 Thermal Energy

2 Heat Heat: transfer of thermal energy from one object to another because of temperature differences Heat flows spontaneously from hot objects to cold objects Why does a cold drink become warm?

3 Temperature Temperature: measure of how hot or cold an object is compared to a reference point Reference points for Celsius are freezing and boiling points of water Reference point for Kelvin is absolute zero which equals 0 K

4 Temperature Temperature is related to average kinetic energy of particles KE of particles is due to random motion through space As an object heats up the particles move faster = higher KE of particles = higher temperature

5 Thermal Energy Thermal energy = total potential and kinetic energy of all the particles in an object Depends on the mass, temperature and phase (solid,liquid,gas) of an object

6 Thermal Energy Example
Cup of tea Temp of 110°F KE of particles 80 J Thermal Energy lower Tea pot full of tea Temp of 110°F KE of particles 80 J Thermal energy higher

7 Thermal Contraction and Expansion
As temp decreases the particles move slower causing less collisions Balloon outside on a cold day Thermal Expansion As temp increases the particles move faster and spread apart Balloon brought in from cold into warm room Gases expand more than liquids and liquids expand more than solids Thermal expansion is used in thermometers to show temperature

8 Measuring Heat Changes
Calorimeter is used to measure changes in thermal energy Uses the principle that heat flows from hotter to cooler objects until they reach the same temperature

9 Specific Heat Specific Heat: Amount of heat needed to raise the temperature of 1 gram of material by 1 degrees Celsius The lower the specific heat the more its temperature rises Unit is joules per gram per degree Celsius J/g°C

10 Specific Heat Q = m x c x T Q = heat absorbed by material (Joules)
m = mass of material (grams) c = specific heat (J/g °C) T = change in temperature

11 Specific Heat An iron skillet has a mass of grams. The specific heat of iron is J/g °C. How much heat must be absorbed to raise the skillet’s temperature by 95 degrees Celsius? Q = m x c x T Q = (500) (0.449) (95) Q = 21, J

12 Specific Heat In setting up an aquarium, the heater transfers 1,200,000 joules of heat to 75,000 grams of water which has a specific heat of 4.18 J/g °C. What is the increase in the water’s temperature? 1,200,000 = (75,000) (4.18) (T) Change in temp = 3.8 °C

13 Specific Heat 34,000 J of heat is absorbed by a 750 g iron skillet when it’s temperature rises from 25°C to 125°C. What is the specific heat of the iron skillet? 34,000 = (750) (c) (100) 34,000 = 75,000 (c) 0.45 J/g°C = c

14 Heat Transfers Conduction Convection Radiation

15 Conduction Conduction: Occurs within a material or between materials that are touching Collisions between particles transfer thermal energy without any overall transfer of matter Conduction is slower in gases than in liquids or solids because the particles are farther apart Conduction is faster in metals because the electrons are free to move around

16 Conduction Thermal conductors: material that conducts thermal energy well Wire rack in oven Pots and pans Aluminum and copper Not all thermal conductors are hot Tile floors Feel cold because they are transferring thermal energy rapidly away from your skin

17 Conduction Thermal insulators: material that conducts thermal energy poorly Air Wooden spoon Wool Plastic foam cups Use trapped air to slow down conduction

18 Convection Convection: transfer of thermal energy when particles of a fluid move from one place to another Fluids = liquids or gases Convection currents: fluid circulates in a loop as it heats up and cools down

19 Radiation Radiation: transfer of energy by waves moving through space
All objects radiate energy. As the temperature increases, the rate at which it radiates energy increases

20 Thermodynamics Study of conversions between thermal energy and other forms of energy Zeroth law: two systems in thermal equilibrium with a third system are in thermal equilibrium with each other

21 Thermodynamics 1st law: Energy is conserved
2nd law: Thermal energy can flow from colder objects to hotter objects only if work is done on the system 3rd law: Absolute zero cannot be reached

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