Thermal Energy Thermal energy results from the random movement of particles in a substance Factors Affecting the thermal Energy of A SUbstance Factor Factor Variation Result Number of Particles ID: 326122
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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.