Cond/Conv/Rad
You feel the sun warming your face. What type of heat transfer is occuring?
Radiation
How does thermal energy move in heat transfer?
From warmer objects to colder objects
What is thermal equilibrium?
When two objects stop transferring heat together because they have reached a balanced temperature.
What unit do we use to measure heat, work, and energy?
What's Ms. Knight's favorite color?
PINK!!
A room is heated by a radiator. The air closest to the radiator warms, rises, and is replaced by cooler air. Identify the transfer method and explain why the air moves.
Convection. Warm air expands and becomes less dense than the surrounding cooler air, so it rises while cooler, denser air moves in to replace it.
Which type of heat transfer occurs through direct contact?
Conduction
A person wears a black shirt and a white shirt outside on a sunny day. Under otherwise similar conditions, the black shirt may become warmer. Which method of heat transfer initially brings energy from the Sun to the shirts, and why can their temperatures differ?
Radiation. Different colors and surfaces absorb and reflect different amounts of incoming radiation; a black shirt often absorbs more sunlight than a white shirt.
A warm object has 34 J and a cool object has 12 J. How much energy must transfer to make their amounts equal?
11 J
What did Ms. Knight teach before she came to Wyoming?
Math
An astronaut standing outside a spacecraft can receive energy from the Sun even though space is mostly empty. Explain why convection cannot carry that energy through the vacuum of space.
Solar radiation travels as electromagnetic waves and does not require matter. Convection requires moving particles in a fluid, such as a liquid or gas, which a vacuum does not provide.
What is convection?
A metal pan is heated on a stove. Describe how thermal energy can travel from the bottom of the pan to the water near the top.
Conduction transfers energy through the metal pan and into the water touching it. Convection currents then circulate the water, carrying thermal energy upward.
A warm object has 46 J, and a cool object has 18 J. How much energy must transfer for their amounts to become equal?
14 J
What's Ms. Knight's favorite kind of Jolly Rancher?
Cherry!
A student wraps one cup of hot water in a thick towel and leaves another identical cup uncovered. Predict which cup will cool more slowly and explain how the towel changes energy transfer.
The wrapped cup should cool more slowly because the towel acts as an insulator, reducing heat transfer (conduction) between the water and its surroundings.
A student places a metal spoon and a wooden spoon into equally hot bowls of soup. After two minutes, the metal spoon feels hotter. Explain why, even though both spoons have been in the same soup.
Metal generally conducts thermal energy much more efficiently than wood, so energy transfers to the student's hand faster from the metal spoon.
Two identical metal blocks have different temperatures. One is at 80°C and the other is at 20°C. They are placed in contact inside an insulated container. Explain what happens at the particle level and why the blocks eventually stop changing temperature.
Faster-moving particles in the warmer block transfer energy through interactions with particles in the cooler block. Energy moves from warm to cool until both reach the same temperature, establishing thermal equilibrium.
A warm object has 125 J and a cool object has 47 J. Calculate the energy transferred to equalize their energy amounts. Then calculate the final amount of energy in each object.
The energy transferred: 39 J
The final amount of energy: 86 J
What's Ms. Knight's favorite holliday?
Halloween!!
A student holds their hand above a candle and then holds it beside the candle without touching the flame. Explain which heat transfer methods may be important in each position and why the results can differ.
Above the flame, convection carries hot gases upward toward the hand. Beside the flame, radiation is especially important because the rising hot gases move mainly upward. The hand may also receive energy from hot gases depending on air movement.
What specific type of electromagnetic waves do we use to see thermal energy?
Infrared
Two objects have reached thermal equilibrium. A student says, "The particles have stopped moving, so no energy transfers." Identify both errors in this explanation.
Particles still move and interact. Thermal equilibrium means there is no net transfer of thermal energy between the objects, not that all particle motion or microscopic energy exchange has stopped.
Two objects begin with 96 J and 28 J. After energy transfer, the warmer object has 61 J. How much energy did it lose, and how much energy did the cooler object gain? Do the final amounts represent equal energy?
The warmer object transferred 35 J, causing the colder object to reach 63 J. The final amounts are not equal, so the objects have not reached equal energy amounts.
What are Ms. Knight's green figures called? (you have to pronounce them correctly to get the point)
Smiskis