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Ahmed saied Sat 06 Nov 2010, 4:37 amHeat Energy:
- Heat is a form of energy.
- Heat transfers from an object of higher temperature to another of lower temperature.
- Heat transfer stops when the temperature of them becomes equal.
Heat Energy:
- It is a form of energy which transfers from the object of higher temperature to that of lower one.
- The sun is the main source of heat on the Earth's surface.
- If you rub your hands together for one minute you feel that your hands get warmer.
- Friction turns the mechanical energy into heat energy.
- The movement of particles and friction between them produce heat energy, by increasing the movement (increasing the kinetic energy), the temperature of particles increases.
The Temperature :
- It is the condition which states the direction of heat energy whether from or to the object when it comes in contact with another. It is directly proportional to the kinetic energy of the particles.
- The temperature can be measured by using thermometers.
Methods of transferring heat through different media:
1. Conduction.
2. Convection.
3. Radiation
. 1) The transfer of heat by conduction:
- It is a method by which heat is transferred through solids from the part of higher temperature to that of lower temperature (without the transfer of the molecules of the substance).
- Cooking pans are made of copper and aluminum because they are good conductors for heat.
2) The transfer of heat by convection:
- It is a method by which heat is transferred through liquid and gases (by the movement of molecules).
- The heat is transferred by rising up the hot molecules (with less density) and falling down of the cold molecules (have more density).
On heating a liquid:
The molecules of the liquid move away from each other, so the liquid expands and its density decreases and become lighter, so it rises up to be replaced by cold liquid.
On heating air (gases):
Hot air (of low density) rises up and replace by cold air (of high density) which falls down.
Applications:
- Air conditioners are fixed at the upper part of the room.
- The freezer of the fridge is found at the top of the fridge.
- The eclectic heater is placed at the bottom of the room.
3) The transfer heat by radiation:
- It is a way by which heat is transferred through gases and space (it doesn't need any material medium to transfer through).
- The heat of the sun is not transferred by convection because the space between the sun and the atmosphere of Earth does not contain any matter through which heat could be transferred.
Heat in our life:
From the sources of heat energy:
- The solar energy (permanent source of energy).
- The petroleum fuel (non - renewable source of energy).
- The electricity (renewable source of energy).
Some examples of technological application which depend on heat energy:
- Electric heater: converts electricity into heat energy.
- Solar heater: converts solar energy into heat energy.
- Electric stove: converts electricity into heat energy.
- Gas stove (gas oven): converts chemical energy into heat energy.
Examples illustrate that the solar energy is essential for other forms of energy:
1- In plants, the solar energy is stored as chemical energy by the photosynthesis process.
2- In fuels as petroleum oil, the soar energy is stored as a chemical energy.
3- Solar energy is responsible for evaporation of water from seas, oceans and rivers to form clouds.
4- Solar energy is the reason for the movement of the wind which is used to generate electric energy.
Technological application on changing the solar energy into other forms of energy:
1- Producing electricity by using solar cells.
2- Providing satellites and space ships.
3- Operating solar heaters.
4- Desalination of sea water (to get fresh water
- Heat is a form of energy.
- Heat transfers from an object of higher temperature to another of lower temperature.
- Heat transfer stops when the temperature of them becomes equal.
Heat Energy:
- It is a form of energy which transfers from the object of higher temperature to that of lower one.
- The sun is the main source of heat on the Earth's surface.
- If you rub your hands together for one minute you feel that your hands get warmer.
- Friction turns the mechanical energy into heat energy.
- The movement of particles and friction between them produce heat energy, by increasing the movement (increasing the kinetic energy), the temperature of particles increases.
The Temperature :
- It is the condition which states the direction of heat energy whether from or to the object when it comes in contact with another. It is directly proportional to the kinetic energy of the particles.
- The temperature can be measured by using thermometers.
Methods of transferring heat through different media:
1. Conduction.
2. Convection.
3. Radiation
. 1) The transfer of heat by conduction:
- It is a method by which heat is transferred through solids from the part of higher temperature to that of lower temperature (without the transfer of the molecules of the substance).
- Cooking pans are made of copper and aluminum because they are good conductors for heat.
2) The transfer of heat by convection:
- It is a method by which heat is transferred through liquid and gases (by the movement of molecules).
- The heat is transferred by rising up the hot molecules (with less density) and falling down of the cold molecules (have more density).
On heating a liquid:
The molecules of the liquid move away from each other, so the liquid expands and its density decreases and become lighter, so it rises up to be replaced by cold liquid.
On heating air (gases):
Hot air (of low density) rises up and replace by cold air (of high density) which falls down.
Applications:
- Air conditioners are fixed at the upper part of the room.
- The freezer of the fridge is found at the top of the fridge.
- The eclectic heater is placed at the bottom of the room.
3) The transfer heat by radiation:
- It is a way by which heat is transferred through gases and space (it doesn't need any material medium to transfer through).
- The heat of the sun is not transferred by convection because the space between the sun and the atmosphere of Earth does not contain any matter through which heat could be transferred.
Heat in our life:
From the sources of heat energy:
- The solar energy (permanent source of energy).
- The petroleum fuel (non - renewable source of energy).
- The electricity (renewable source of energy).
Some examples of technological application which depend on heat energy:
- Electric heater: converts electricity into heat energy.
- Solar heater: converts solar energy into heat energy.
- Electric stove: converts electricity into heat energy.
- Gas stove (gas oven): converts chemical energy into heat energy.
Examples illustrate that the solar energy is essential for other forms of energy:
1- In plants, the solar energy is stored as chemical energy by the photosynthesis process.
2- In fuels as petroleum oil, the soar energy is stored as a chemical energy.
3- Solar energy is responsible for evaporation of water from seas, oceans and rivers to form clouds.
4- Solar energy is the reason for the movement of the wind which is used to generate electric energy.
Technological application on changing the solar energy into other forms of energy:
1- Producing electricity by using solar cells.
2- Providing satellites and space ships.
3- Operating solar heaters.
4- Desalination of sea water (to get fresh water
