Thermal Energy - PowerPoint Presentation

Slide1

Thermal EnergySlide2

Thermal Energy

Thermal energy results from the random movement of particles in a substanceSlide3

Factors Affecting the thermal Energy of A

SUbstance

Factor

Factor Variation

Result

Number of Particles

More particles

Increased thermal Energy

Less particles

Less

thermal energy

Temperature

Higher Temperature

Increased thermal energy

Lower Temperature

Reduced thermal energySlide4

Thermal Energy

THERMAL ENERGY is the energy contained in a substance, determined by the number of particles in the substance and their temperature

Thermal energy can be transferred from an environment where the temperature is high to an environment where the temperature is lower until the two environments have the same temperatureSlide5

Videos

http://www.youtube.com/watch?v=YWJHNG5y5F0&feature=related

http://www.youtube.com/watch?v=rU-sPzshVnM&feature=relatedSlide6

Temperature & HEAT

People often confuse temperature and heat

When the temperature is high people say “ it’s hot!”

Temperature takes into account only the speed of particles in a substance

Heat depends not only on the speed of particles ( degree of agitation) but also on their mass (number of particlesSlide7

Question

If a cup of coffee and a red

popsicle

were left on the table in this room what would happen to them? Why?Slide8

Heat

Heat is the transfer of thermal energy between 2 environments with different temperatures.

Heat always passes from the warmer to the cooler environmentSlide9

Heat

Energy

How much heat energy an object has depends on its temperature AND how much of it there is…

The sparkler is at a higher temperature than the bath, but the bath has a large volume of water, so it stores more heat energy.Slide10

Q. Which has the highest temperature – spark/kettle of water?

Q. Which has the most heat energy – spark/kettle of water?

Look at the picture of the kettle and the fire.

Think

about:

one of the sparks from the fire and

the kettle full of boiling water.Slide11

Heat Transfer

Heat can transfer 3 waysSlide12

Conduction

Conduction involves the transfer of heat through direct contact

Heat conductors conduct heat well, insulators do notSlide13

Convection

Takes place in liquids and gases as molecules move in currents

Heat rises and cold settles to the

bottom

As a gas or liquid is heated it warms, expands and rises because it is less dense

When the gas or liquid cools, it becomes denser and falls.

As the gas or liquid warms and rises, or cools and falls, it creates a convection current.Slide14

Radiation

Electromagnetic waves travel through empty space Slide15

Practice

Wrap a fur coat around a thermometer. Will its temperature rise? Explain why or why not.

If you hold one end of a metal nail against a piece of ice, the end in your hand soon becomes cold. Does cold flow from the ice to your hand? Explain.Slide16

Answer

No, the thermometer will not heat up because it is the same temperature as the coat. There has to be a difference in temperature in order for heat transfer to take place

No, cold does not flow. Heat flows from your hand to the nail to the ice. Since your hand is losing heat, it feels cold. HEAT is the only thing that flows.Slide17

Practice Question

Explain why “firewalkers” can walk safely across a bed of red-hot coals in bare feet. Slide18

Answer

Because the rate of heat transfer is slow, because coals are not very good conductors. If they walk fast enough, there is only a small amount of heat transferred to their feet, and they do not burn.Slide19

Practice Question

If heat transfers from hot to cold, and stops when the two objects reach the same temperature, explain why it is possible for the inside of your car to be hotter than the air outside on a hot summer day.Slide20

Answer

The greenhouse effect. Electromagnetic waves from the sun enter your car through the windows and are absorbed by the seats and other objects in the car. They then re-emit electromagnetic radiation of a different wavelength that cannot pass through glass. All of that energy is therefore trapped inside the car, causing the temperature to rise.Slide21

Practice Question

Since a hot cup of tea cools more rapidly than a lukewarm cup of tea, would it be correct to say that a hot cup of tea will cool to room temperature before a lukewarm cup of tea will?Slide22

Answer

No, because as it cools, the rate of heat transfer slows down until it is just as slow as the lukewarm cup of tea. The only way to make it cool faster is by introducing convection. Slide23

Practice Question

The Concorde supersonic airplane is 20 cm longer when in flight. Explain why.Slide24

Answer

As the jet flies, it experiences a huge amount of friction, which heats it up significantly. This causes thermal expansion, and the plane lengthens.Slide25

Practice Problem

If you drop a hot rock into a pail of water, the temperature of the rock and the water will change until both are equal. The rock will cool and the water will warm. Is this true if the rock is dropped into the Atlantic Ocean?Slide26

Answer

Yes, yes, yes!!! Even though the Atlantic ocean is huge, the heat that leaves the rock enters the water (law of conservation of energy). This means that the temperature will increase. Since the ocean is a huge body of water, it will be an incredibly small change, but a change nonetheless.Slide27

Practice Problem

When you step out of a swimming pool on a hot, dry day, you feel quite chilly. Why?Slide28

Practice problem

The water will start evaporating in the air. Evaporation requires energy (heat) and that heat will come from your body. Since you are losing heat, you will feel cold.Slide29

Practice Problem

Does a gas give off or absorb energy when it turns into a solid?Slide30

Answer:

It gives off energy, because it is going from high energy to low energy.