Science? heat quiz?

i have a science quiz on heat tomorrow. and she gave us some questions that may be on the quiz. so im going to post it hear and if you know the answer.. please let me know.

1) explain what a calorie really is?

2) Give examples of conduction?

3) Give examples of convection?

4)Give examples of radiation?

5)why do they put metal gaps on bridges?

6) why are the electrical wires on telephone poles loose?

7) why do you put a metal top of a jar under hot water to open it easier?

i need scientific answers , so if you know anything, please let me know. I will gladly appreaciate it. Thanks, =]

Science? heat quiz?

1. A calorie is the amount of heat (energy) needed to raise the temperature of one gram of water by 1 degree Celcius. It is interesting that the "Calories" spoken of in nutrition circles are really kilocalories. 2. If you put your hand on a hot iron and it gets burnt you can blame conduction. The heat has been transferred from the metal to your skin because you touched it. 3. When you warm you tootsies on the floor register on a winter day, heat is delivered to your feet thru forced convection from the heating system. On a hot summer day, you can see the effects of free convection on a distant patch of pavement because the air gets lumpy and wavy as it rises from the hot pavement. 4. If you stand near a hot campfire or near a hot stove, you can "feel" the heat coming off it. Same thing when you stand in the warm sunlight. Heat is delivered to you body thru radiation. 5. Gaps in metal bridges or railroad tracks are there to allow the metal to expand on hot summer days without causing things to buckle and warp. 6. If you strung overhead wires tightly on a summer day, they would shrink and possibly snap on a cold winter day. 7. Hot water on a metal lid will cause the lid to grow a bit and more easily loosen its grip on the glass jar. Not everything expands at the same rate as it is heated. Aluminum grows at a rate about twice that of steel. Glass does not grow as much as either of them. Pyrex glass is special glass that does not want to grow much at all in response to thermal change, so it will not crack when you pour hot water into it (within reason!).

Science? heat quiz?

Calorie: It is a unit of heat defined as the quantity of heat required to raise the temperature of 1 gram of water by 1 degree Celsius at atmospheric pressure

Conduction: Heat conduction is the spontaneous transfer of thermal energy from hot region to cold region. When you touch something hot and feel the heat is because of conduction. When you heat a metal rod at one end but the rod gets heated at the other end too is due to conduction.

Convection: The transfer of heat through a fluid caused by molecular motion. Convection is applicable only for liquids and gases unlike conduction which is for solids. When you heat water in a vessel from below but find the water at the top hotter is due to convective currents. Sweat on your skin dries when you are exposed to air is convection. A refrigerator cooling food is by convection. If you stick your hand outside your car and your hands cool it is due to convection.

Radiation: It is thermal energy (heat) that is radiated or transmitted in the form of rays or waves or particles. When you stand next to a fire and feel the heat is due to radiation. A light bulb when glowing gives heat by radiation. If you go near a hot object you feel the heat which is due to radiation.

why do they put metal gaps on bridges?: Because the metals expand during the day (due to heat from sun) %26amp; summer and contract during the night %26amp; winter. It is allowance for the metal to freely expand and contract.

why are the electrical wires on telephone poles loose?: It is also to allow for free expansion and contraction.

why do you put a metal top of a jar under hot water to open it easier?: Because metals expand on heating and the clearance between the threads will increase thus reducing friction and making it easier to open with less force.