Heat & Temperature

Contents

The kitchen story

One day, Sunil’s mother was ill and he had to the kitchen work of that day. Sunil’s sister was having exams and she was studying. His father was out of town for work. That day Sunil had to take care of everything, but he never cooked food and nor did he ever enter the kitchen. He did not know what to do because he thought it isn’t his duty but IT IS.

Sunil knew how to turn on the stove and put milk to boil and he did it. After some time he took a small spoon and took some milk in it, put that on his tongue and the milk was so hot that it burnt his tongue. He saw the milk on the stove again but it was still looking normal, he was confused how it looked the same but was very hot, he thought that stove fire was below and how the milk above get hot? Sunil suddenly had so many questions in his mind. It was very hot outside and Sunil went near the water tank and put his hand inside. The water above was hot due to the sun, but as his hand went deeper, he felt the water was cooler.

That day was very confusing for him, Sunil also went to the refrigerator and took some ice. The ice was very cold. He put an ice cube on a pan that was on the stove it got melted into water. He accidentally threw some ice on the table but those were still ice cubes.

That day Sunil tried very hard and learned how to cook, everyone was proud of him. But he had so many questions about hot and cold and temperature.

Think:

What do you think made Sunil’s tongue burn?
Why was the water cool deep inside the water tank?
Why did the ice cube on the hot pan melt and that on the table did not?
When do you say something is HOT?

HEAT

Heat is a form of Energy. When an object has more heat energy, it is hot. If it has less heat energy, it is cool.

How does a body get heat energy?

Heat energy is a form of energy that travels from one object to another. And if one object has to get more heat energy then some other object should give its heat energy to this object. Heat energy always travels from a hot object to a cooler object for example, for the milk to get more heat energy and boil, the hot container in which the milk is put gives its heat energy to the milk and the milk gets hot.

How do you think the container got its heat energy?

In the season of summer, we all know that everything gets hot. The varenda outside our house and the roads and the rooms we live in, everything gets hot. This is because during the summer season, the sun is closer to us and more of the sun’s heat energy travels to earth and everything is hot in summers.

But the road which is under the direct sun gets hotter than the floor under a tree, where there is less sunlight and more shade. When it is very hot and we are tired we go and stand or sit under a tree because under a tree there is shade, and it is cooler. Which is why we need to have more trees so that we can have more shade.

But the road/floor under the tree and the floor/road in direct sunlight are the same! How can we know if it is really cooler under the tree? We know that the sun’s heat energy travels to earth by light and under a tree, there is less light so it is cooler under a tree.

But, how can we know how hot an object is? How can we know if it has more or less heat energy?

If I give you two bowls with water, how do you know which one is HOT and which one is COLD?

TEMPERATURE

Temperature is the measure of how hot or cold an object is. When we measure an object’s temperature, it tells us if the object is hot or cold. In the above example where I give you two bowls of water and you should know which one is hot and which is cold. You just have to measure the object’s temperature.

Temperature measures the heat energy of an object and shows us a number, with which we can understand how hot/cold the object is. If the number is big then the body is hot, and if the number is small then the object is cold.