NCERT Solutions for Class 5 EVS Chapter 15 Blow Hot, Blow Cold

QUESTIONS FROM TEXTBOOK SOLVED

Do This
1.Have you warmed your hands in winter by blowing on them when they are cold? How does it feel?
Ans. Yes, I have warmed my hands in winter by blowing on them when they are cold. It feels quite comfortable.

2.Blow hard from your mouth onto your hands. How did you find the air from your mouth as compared to the air around? Was it hotter or cooler?
Ans. When I blow hard from my mouth onto my hands; the air from my mouth feels hotter as compared to the air around.

3.Now put your hands at some distance from your mouth and blow again. Does the air from your mouth feel warm? Why?
Ans. When hands are put at some distance from the mouth; the air blown from the mouth does not feel much warm. This happens because the air travels some distance and gets mixdd up with the air around.

Think and Tell
1.Can you think of any other way in which you use the warmth from your breath?
Ans. Yes, I can think of another way in which the warmth from breath is used. When someone gets redness in eyes or some minor injury, then a part of handkerchief is warmed by blowing air over it. The warm handkerchief is used to provide warmth to eyes or the injured part. This gives Some relief.

2.Fold a piece of cloth 3-4 times. Now bring it close to your mouth and blow hard on it. Did the cloth become warm?
Ans. Yes, the cloth became warm.

3.Balishtiye saw that the woodcutter was trying to cool the hot potatoes by blowing on them. What would have happened if he had eaten the potatoes without cooling them?
Ans. Eating the potatoes without cooling them could cause burns in the mouth.

4.Have you ever burnt your tongue when you ate or drank something that was too hot? How do you cool some food when it is too hot?
Ans. Yes, sometimes I have burnt my tongue while eating hot pakodis or sipping hot tea. I usually cool the hot food by blowing over it. Sometimes, we also use a fan to cool the food.

5.If you were to cool these three hot things—dal, roti, rice—in which ways would you do so?
Ans. These food can be cooled either by blowing over them or by using a fan. They should be preferably kept in a broad container.

6.For what other things do you blow air from your mouth?
Ans. Some of the other activities which can be done by blowing air from mouth are as follows:
(a) Whistling
(b) Playing with a firkin
(c) For removing dust from something
(d) For cleaning the spectacles.

Picture 1:

7.Mini tried to cool her tea by blowing on it. Which do you think will be hotter—Mini’s tea or the air she blew from her mouth?
Ans. Mini’s tea would be hotter than the air she blew from her mouth.
Picture 2:

8.Sonu was feeling very cold. He kept blowing on to his hands. Now think and write, which will be cooler—Sonu’s hands or his breath?
Ans. Sonu’s hand will be cooler than his breath.

Blow in Different Ways
1.Make whistles of the things given below. Write in a sequence—from the loudest to softest whistle.
— Wrapper of a toffee
— A leaf — A balloon
— The cap of a pen
— Any other thing
Ans. Do it yourself.You can also try many other items like paper, banana leaf, etc.

2.Have you seen people playing different musical instruments like flute, dholak, been…guitar, mridang, etc. Can you recognise their sounds with your eyes closed? Find out more about these musical instruments. Collect their pictures too.
Ans. Yes, I can recognise the sounds of flute, dholak, been, guitar, mridang, etc.
Some of the instruments are discussed below:
Flute: It is made of bamboo and is played by blowing air in it. It is a type of wind instrument.

Dholak: It is made of wood and a membrane of leather. It is played by beating on the leather membrane. It is a type of percussion instrument.

Been: It is made of dry pumpkin which is hollowed out. It is a type of wind instrument.

Guitar: It is made of wood and metal strings. It is a type of string instrument.

Write
1.Can you name some things which produce melodious or pleasing sounds when we blow into them?
Ans. Musical instruments which come under the category of wind instrument produce melodious sound when we blow air into them, e.g. flute, shehnai, saxophone, mouth organ, clarinet, etc.

Do This and Discuss
1.Have you seen someone blowing on their spectacles to wipe them clean? How does the air from the mouth help in cleaning the spectacles?
Ans. Yes, I have seen my grandfather blowing on his spectacles, to wipe them clean. The air blown from the mouth is hotter than the glass of the spectacles. The air blown from the mouth also contains moisture. When the moisture touches the colder glass surface it turns into fine water droplets. These water droplets help in cleaning the glass.

2.Take a glass. Bring it near your mouth and blow hard on it. Do this, two or three times. Does the glass look hazy?
Ans. Yes, the glass looks hazy after blowing on it two to three times.

3.Can you make a mirror hazy in the same way? Can you tell by touching the mirror what made it hazy? Is the air you blew from your mouth dry or wet?
Ans. Yes, I can make a mirror hazy in the same way. On touching the mirror some moisture sticks to fingers also which shows that the moisture turned the mirror hazy. It also shows that the air blow from my mouth is wet.

4.Put your hand on your chest. When you breathe in, does your chest come out or go in?
Ans. When I breathe in, my chest comes out.

5. Measure Your Chest:
(а)Take a deep breath in.
(b)Ask your friend to measure your chest with a thread. Measurement:…….
(c)Now breathe out. Again ask your friend to measure your chest. Measurement:………
(d)Was there any difference in the two measurements of your chest?
Ans. Do it yourself.You will find that the chest measures more when you breathe in than when you breathe out.

How Many Breaths in One Minute?
1.Put your finger under your nose. Can you feel any air when you breathe out from your nose?
Ans. Yes, I can feel the air when I breathe out from my nose.

2.Count how many times in one minute do you breathe in and breathe out?
Ans. I breathe in and out about 20 times in a minute.

3.Jump 30 times. Did you feel breathless?
Ans. On jumping 30 times, I feel breathless.

4.Now again count how many times in one minute you breathed in and out?
Ans.After jumping 30 times, I breathed about 30 times in a minute.

5.What was the difference in your count before and after jumping?
Ans.  I breathed in and out about 10 times more than what I did normally. It shows that jumping increased my rate of breathing.

The Clock Inside You
1.You have all heard the ‘tick tick’ of the clock. Have you seen a doctor using a stethoscope to listen to your chest? What do you think she hears? Where is the – sound coming from? Is there a clock inside your chest that keeps ticking away?
Ans. Yes, I have seen doctors using a stethoscope to listen to a person’s chest. The doctor hears the heartbeat. The sound of the heartbeat comes from the heart. Heart is not a clock, but an organ which is on the left side of the chest.

2.Do you want to listen to your heartbeat? Take a rubber tube as long as the distance from your shoulder to your elbow. At one end of the tube fix a funnel. Place the funnel on thd left side of your chest. Put the other end of the tube to yoUr ear. Listen carefully. Did you hear a dhak dhak sound?
Ans. Yes, I can hear the dhak dhak sound.

Snake Tells the Flow of Air
1.Stand with this snake below a fan. Look in which direction it moves. Take this paper snake to different places and observe its movement.
Ans. When the snake is kept below a fan, it moves in anticlockwise direction. This happens because the air is moving in the downward direction.

2.Can you understand from the movement of the snake—if the air is moving upwards or downwards?
Ans. When the snake is moving in clockwise direction, it means the air is moving upwards. When the snake is moving in anticlockwise direction, it means the air moving downwards.

What We Have Learnt
While playing, Amit hit a wall. His forehead was swollen. Didi immediately folded a scarf (4—5 times), blew on it and kept it on Amit’s forehead. Why do you think Didi did this?
Ans. After blowing air on the scarf, the scarf becomes warm. Pressing with a warm scarf would have given some relief to Amit’s forehead. That is why Didi did this.

2.We blow to cool hot things as well as to warm them. Give examples of each.
Ans. Examples, when we blow to cool hot things: A cup of tea and hot food.
Examples; when we blow to warm cool things: Our hands in winter, a piece of cloth.