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Answers to Readers' Questions on Physical Science:

Heat Transfer

The following 60 comments and questions have been sent in. They are listed according to date.

List of first 10 items

• Quiz boring for me
• Difference between conduction and convection
• Temperature diminishes when the light comes on
• Does a hot object cool faster in freezer or refrigerator?
• Best conductors of heat
• Describe that energy is transferred
• Heat conductivity of copper versus glass
• What happens if a balloon is placed in a refrigerator?
• Why do bare feet feel colder on a stone floor?
• Rate of melting and surface area

Next 10

Quiz boring for me

Question

November 10, 2009

your quiz is really stupid and boring it needs more questions and abit harder the quiz is too easy to do because you just click each button and see which one is right .you should just be able to click the answer that you think is right and then move on to the next one then you should show the correct and incorrect answers when you have finished the qiuz.

Jesse - New Zealand

18647

Answer

I'm sorry you found the quiz boring. It probably is too easy for you. We do have harder graded tests available for most science subjects.

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Difference between conduction and convection

Question

March 3, 2009

what is the difference between conduction and convection

- USA

17371

Answer

The lesson should explain that.

Conduction is exchange in solids. Convection is exchange in a gas or liquid from its motion.

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Temperature diminishes when the light comes on

Question

December 30, 2008

When you are in a hot room where is no light,as the light comes, the hotness of the room diminishes.so what cause this?

Mujib Rabiu - Nigeria

17021

Answer

Much of this depends on where the heat is coming from. Infrared radiation cannot be seen by the eyes but is the source of heat that is radiated off of walls in the ground. If the walls are still hot, it should not matter if there is visible light on them also. In fact, you would expect the temperature to rise.

There is information missing in your question. Is the heat because the air is hot? Or is the heat due to the walls of a room being warm? It is hard to see it that if a room is let's that the temperature will decrease.

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Does a hot object cool faster in freezer or refrigerator?

Question

December 2, 2008

Generally speaking, will objects placed in a freezer get colder faster than objects placed in a refrigerator, understanding that eventually, the object will get colder in time? I was under the impression that objects lose or gain heat at a rate specific to its make-up, regardless of the temperature differences.

Don - USA

16886

Answer

An object will be cooled both by conduction or contact with a cold surface and by convection and movement of the cold air.

The rate of conduction heat flow is H = k*A*dt/x, where k is the thermal conductivity of the material, A is the cross sectional area, dt is the difference in temperatures and x is the thickness.

In other words, the material and temperature difference are factors in the rate the object cools.

You also would have to take into consideration air movement in both the freezer and refrigerator section. Some units have fans that would increase the convection currents.

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Best conductors of heat

Question

August 31, 2008

pleas inform me the ten best conductors of heat.
thanks in advance

paraskevas - Greece

16430

Answer

Metals are the best conductors of heat. The best conductors of electricity are the best conductors of heat. Gold, silver, copper and aluminum are good conductors.

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Describe that energy is transferred

Question

June 23, 2008

how to describe that energy is transferred in the process of conduction, convection and radiation.

nuha - Maldives

16128

Answer

You can measure the amount of energy transferred. The process of conduction, convection or radiation describes how the energy is transferred.

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Heat conductivity of copper versus glass

Question

June 14, 2008

Hi Iam Raj,
I have somequestions,please answer them.
1]Pieces of copper and glass are heated to the same temprature. Why dose piece of copper feel hotter on touching?
2]At what temprature the block of wood and block of metal feel equally cold or equally hot on touching?
3]why are woolen cloth warmer than cotton cloth?
4]A blanket which keeps us warmer inwinter is able to protect ice from melting. Please Explain.
5]can water be boiled inside earth's satelite by convection?
6]On a winter night you feel warmer when clouds cover the sky than when sky is clear? Why?

Raj - India

16089

Answer

Copper conducts heat much better than glass. Thus, it will transfer that heat to other objects such as your hand more readily, making it feel hotter. The thermal conductivity of wood is only 0.4 while copper is 400. I do not have the equations for to tell what temperature they would feel the same.

Wool is a better insulator than cotton.

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What happens if a balloon is placed in a refrigerator?

Question

April 9, 2008

1.if the balloon is placed in refrigerator what will occur?
2.thermal diffusivity of liquids compared with gases?

muthukannan - USA

15693

Answer

The balloon will get smaller as the gas inside gets colder. Also, since gas molecules are usually further apart than liquid molecule, the diffusion of energy (thermal diffusivity) is greater in a liquid.

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Why do bare feet feel colder on a stone floor?

Question

March 29, 2008

1-how is the hot water supplied to the house.
2-explaine why our bare feet feel cold on stone floor but not on a carpet.
3-people often say worm clothing keep out the cold and why is this expression unsuitable for scientific purposes and what do they realy mean.

messaoud - Morocco

15629

Answer

A water heater makes the water hot by convection. Hot water is flows to the faucet from a separate water pipe than is cold water.

Carpeting is an insulator from the cold. Also, the transfer of heat (or cold) is not effective from a carpet, while there is much heat or cold transfer between the stone floor and the feet.

Warm clothing is an insulator and prevents much of the body heat from escaping. But it also prevents the cold air from cooling the body.

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Rate of melting and surface area

Question

February 13, 2008

MY SON IS DOING A SCIENCE FAIR PROJECT ON "WHICH SHAPE OF ICE CUBE MELTS THE FASTEST? ALL THE SHAPES HAVE THE SAME AMOUNT OF WATER HOWEVER, THE SHAPE THE WATER WAS PUT IN DIFFER. WE FOUND OUT THAT THE SMALLER THE SURFACE AREA THE SLOWER THE MELTING RATE. WE NEED TO KNOW WHY? WE WOULD APPRECIATE YOUR HELP.
THANK YOU.

BERNEITTA - Canada

15344

Answer

The molecules on the surface of the ice cube are hit by air molecules or whatever else touched them. The air molecules transfers energy (heat) to the ice molecules until their temperature gets above freezing. The more ice molecules that are exposed to the warm air, the faster the melting process.

A sphere has the smallest surface area per volume. The largest area per unit volume would be a thin sheet of ice.

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