Blow Hot Blow Cold Class 5 EVS Chapter 15 CBSE Notes - 2025-26
FAQs on Blow Hot Blow Cold Class 5 EVS Chapter 15 CBSE Notes - 2025-26
1. What is the main concept to revise from the Class 5 EVS chapter ‘Blow Hot, Blow Cold’?
The key concept to revise is that the air we breathe out can be used to either warm things or cool things down. This depends on the temperature difference between our breath and the object. Our breath is warmer than cold hands, so it warms them. It is cooler than hot food, so it cools the food down.
2. What key scientific principle from the notes explains how the same breath can warm cold hands and cool hot potatoes?
The principle is heat transfer. Our breath has a relatively constant warm temperature. When blown on cold hands, heat moves from our warm breath to our colder hands, making them feel warmer. When blown on hot potatoes, the moving air from our breath helps carry heat away from the potatoes, making them cool down faster.
3. For a quick revision, why does a mirror get foggy when you blow on it?
A mirror gets foggy because the air we breathe out is warm and contains moisture (water vapour). When this warm, moist air hits the cooler surface of the mirror, the water vapour quickly cools down and turns into tiny liquid water droplets. This process is called condensation, and it makes the mirror look foggy.
4. In the chapter summary, why did the woodcutter blow on his hands?
The woodcutter blew on his hands to make them warm. It was a cold day, and his hands were frozen. The warm air from his breath transferred heat to his colder hands, providing relief and making it easier for him to work.
5. What is a 'chulha' as described in the chapter summary?
A 'chulha' is a traditional, simple stove, often made from stones or mud, used for cooking food with firewood or coal. In the story, the woodcutter blows air onto the burning wood in the chulha to provide more oxygen and make the fire burn brighter to cook his potatoes.
6. How does a doctor using a stethoscope relate to the concept of air in this chapter?
A doctor uses a stethoscope to listen to the sounds inside our body, particularly the sound of our heart and the air moving in our lungs. This relates to the chapter's theme of breath and air. While we use our breath to create sound in a flute, a stethoscope helps us hear the sounds created by our body's internal processes, like breathing, to check if we are healthy.
7. Why is understanding the 'blow hot, blow cold' concept useful in everyday life?
Understanding this concept helps us in many daily activities. For example, we use it when we:
- Blow on a hot cup of tea or soup to cool it down.
- Blow on our hands in winter to warm them up.
- Blow out a candle to extinguish the flame.
- Blow gently on a small wound to soothe the stinging sensation.
It's a basic principle of physics that we use instinctively to interact with our environment.
