Hot and Cold Objects
Class 7 Science | Understanding Heat and Temperature
Introduction
Every day we come across objects that feel hot or cold. A cup of tea feels hot while a bottle of chilled water feels cold. But how do we decide whether an object is hot or cold? This is the basis of the chapter Heat in Class 7 Science.
How Do We Sense Hotness or Coldness?
Our skin can feel the difference in temperature, but it is not always reliable. For example, if you put one hand in cold water and the other in warm water, and then place both hands in lukewarm water, they will give you different sensations. That is why we use thermometers for accurate measurement.
“Temperature is the measure of the degree of hotness or coldness of an object.”
Measurement of Temperature
The device used to measure temperature is called a thermometer. The most commonly used one is the clinical thermometer, which is used to measure body temperature.
- Normal human body temperature is 37°C or 98.6°F.
- Temperature is measured in degree Celsius (°C) or Fahrenheit (°F).
Transfer of Heat
Heat always flows from a hot object to a cold object until they reach the same temperature. This transfer takes place in three ways:
- Conduction – Transfer of heat through solids (e.g., a metal spoon becoming hot in boiling water).
- Convection – Transfer of heat through liquids and gases (e.g., heating water in a pan).
- Radiation – Transfer of heat without any medium (e.g., heat from the Sun reaching Earth).
Daily Life Examples of Hot and Cold Objects
- Hot: Tea, fresh soup, heated iron rod.
- Cold: Ice cream, chilled juice, ice cubes.
Conclusion
Understanding hot and cold objects helps us learn the basics of heat and temperature. This knowledge is not only useful in science but also in our daily life—from cooking food to predicting weather and even in medical diagnosis.
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