NCERT Solutions for Class 5 EVS Chapter 15

We see drops of water on the bathroom mirror after taking a hot shower because the water vapour rising from this water touches the cold surface of the bathroom mirror and condenses to form water droplets.

When we breathe in air, our chest expands as the air enters our lungs and takes space inside them.

When we inhale or breathe in, the air enters our lungs and the oxygen present in the air moves from our lungs to our blood. At the same time, carbon dioxide, a waste gas, moves from our blood to the lungs and is exhaled or breathe out. This process is called gas exchange and is essential to life.

When we breathe out the air then are chest contracts as we let the air go out of our blood by exhaling it.

We spread out Khichdi on out plate before eating so as to increase the surface area thus allowing the vapour to escape quickly and it cools down our food.

Evaporation is the process of changing the liquid(water) into water vapour (gas form) on heating.

A doctor uses a stethoscope to listen to the sound of the heartbeat of the patient.

When we bang our head while playing and our forehead gets swollen and has redness then warm air is blown on a part of hanky to give relief from the pain or discomfort. Actually, on blowing, the scarf becomes a little warmer and gives some relief to the pain and swelling.

During any physical work like running, walking faster, exercise etc. the body muscles need more energy, for which more oxygen is required to burn up the glucose to produce energy. Hence, we breathe faster to take in more oxygen to fulfil the energy needs or requirement by the muscles.

We need to blow on our spectacles to wipe them clean because the air that we blow out of our mouth also has water vapour. When the vapours touch the cold surface(glass) of the spectacles, it condenses to form small droplets which we need to wipe from the surface to make it clean.

When we blow on lit damp wood or coal, the unburnt carbon particles in the smoke move away thus making space for fresh air which is rich in oxygen that helps in burning of fire.

Gita’s soup was hotter as compared to the air she blew from her mouth. This helped her to cool her soup. Whereas the temperature outside was colder than Vikas’s breath which helped him to warm his hands. This is how blowing air helps.

The process by which water vapour (gas form) changes into water(liquid) on cooling is called condensation.

When we breathe out, water vapour from our breath condenses as it comes in contact with the cold air of the atmosphere and mist is formed. So, the cold air causes the warm moisture in our breath to condense into tiny droplets of water that appear like a small, misty cloud.

In winter, our hands become very cold. When we open our mouth wide and blow on to our hands there is warm, moist air inside our mouth. The steam of our breath then makes our hands warm in winter.

Breathing is an activity that we do throughout our lives. We start breathing right from the moment, we are born and continue doing so till we die. It is a process that continues automatically. We breathe even when we are sleeping. Breathing is a natural process of inhaling oxygen and exhaling carbon dioxide. We breathe through our nose.

Air like most other substances, expands when heated. Warm air becomes lighter than cold air, and so when air is heated it rises. The air becomes less dense than the air surrounding it and also the distance between the molecules increases. So, the less dense air floats in the much denser air just like ice floats on water as ice is less dense than water.

Air becomes light on heating and there is more space between the molecules. As a result, the air becomes less dense than the surrounding matter and the hot air floats upward. That is why the hot air balloons fly in the sky.

When the air becomes cool, the temperature drops and the molecules move more slowly, taking up less room. The amount of space the air takes up reduces the air pressure. As a result, the air contracts when cooled. And it becomes heavier and comes down.

We blow on a burning fire so that we keep it burning so as to increase the supply of oxygen which is important for burning. A popcorn seller therefore fans the burning coal to increase the supply of oxygen. Thus to increase the supply of air for making the popcorn, the popcorn seller fans them.

The air blown from our mouth is always at our normal body temperature which is 98.7⁰C. Therefore, when we blow at some colder thing in winter its temperature rises and if we blow at some hotter thing its temperature falls.

Been, brass band and flute are the instruments which produce sound when we blow them.

We use the warmth of the breath to cure por reduce the redness of the eye or any injury, by blowing it onto the handkerchief and keeping it on the redness of the eye as it gives relief to us and reduces the pain.

All musical instruments are able to create sound by causing matter to vibrate. The vibrations start the sound waves that move through the air. Most musical instruments use resonance or tone to amplify the sound waves and make the sounds louder. Resonance or the tone occurs when an object vibrates in response to sound waves of a certain frequency.

A flute produces sound when a stream of air goes across a hole in the instrument and creates a vibration of air at the hole.

The movement of the snake in the clockwise direction means that the air is moving upwards. But when the snake is moving in anticlockwise direction, it means the air is moving downwards.

The air that is coming out of the mouth is colder as compared to that of the hot potatoes. So, the air from the mouth cools down the hot potatoes. We blow on some food to cool them or we leave them as it is uncovered to let them cool down in the surrounding atmosphere
We also put some hot food in refrigerator also to cool them.

When we run or jump the blood circulation increases in our body. Our heart has to do more work to pump the blood faster. Therefore, it beats faster.

We can cool down porridge by:
a. pouring it in an open bowl.
b. putting it under the fan.
c. blowing air from the mouth.

When we blow hard on the mirror, some water vapours also come out from our breath and fall on the mirror. This water vapours make the mirror hazy.

We should breathe with our nose than with our mouth because breathing through your nose can help to filter out dust and allergies, boost our oxygen uptake, and dampen the air we breathe in. Breathing through Mouth can dry our mouth and increase our risk of bad breath and gum inflammation.

Burning of coal takes place in presence of oxygen and when we are blowing on it, we are providing it more oxygen therefore it does not die out but burns further.

The air blown from our mouth has moisture in it in the form of water vapours. Thus when we blow air on the mirror surface which is cooler, it allows the vapours to cool down and hence cloudy surface is formed.

All the systems in our body are dependent on oxygen. So, effective breathing is very important as it not only provides us with a greater sense of mental clarity, but also helps us sleep better, digest food more efficiently, improve our body’s immune response, and reduce stress levels.

When we blow air on a burning candle, we are actually removing the hot air around the flame. By doing so, we reduce its temperature below the flash point and thus the candle goes out.

When we blow hard from my mouth onto my hands; the air from the mouth is hotter as compared to the air around.

The air we exhale or breathe out is hot because it is maintained to our body temperature. Exhaled air is warmer than inhaled air because it is the same room temperature air which we have taken in. The air which we breathe out is the air in the lungs which is warmed by core body heat.