It’s AumSum Time. How does a fan give us cool air? Because it has a refrigerator inside it. Oh. You are just unbelievable. First of all, a fan does not give cool air. Our body loses heat mainly in two ways. Firstly, our body heat gets transferred. To the surrounding air through a process of
convection. Secondly, the sweat produced on our skin absorbs
our body heat. And evaporates into air, thus allowing us
to lose heat. Now, without a fan, both of these above ways
create. A stagnant layer of hot humid air around our
skin. Thus making it difficult to continue the processes
of convection and evaporation. However, when we switch on the fan, it blows
away the stagnant layer of hot air. And replaces it with a relatively drier air. Allowing the processes to continue and thus,
we lose more heat and cool down faster. Why does hot air balloon float? Because it has invisible wings. No. It is because of density. Density is the measure of mass present per
unit volume. Lesser the density, lighter will be the object. Now, density varies with temperature. Oh dude. It is so complicated. Alright. I’ll explain. When a hot air balloon is on ground. The air inside and outside the balloon. Is of same temperature and density. However, when we turn on the burner of the
balloon. The air inside the balloon starts getting
hot. The molecules of air move faster and spread
apart, taking up more space. Hence, the air inside the balloon becomes
less dense than the air outside. As less dense air is lighter. The hot air balloon rises and thus, begins
to float. Topic: Electric Charge. How does a plastic comb attract paper? What? You don’t believe me? Ok. Let us try. Take a plastic comb and bring it close to
some pieces of paper. Hey, Wait. Don’t laugh. We need to do something first. Rub the comb on your dry hair. And then bring the comb close to the pieces
of paper. See, I was correct. The pieces of paper got attracted to the plastic
comb. Do you think it is magic? No, the reason behind this is electric charge. Electric charge is the quantity of electricity
held in an object. There are 2 types of electric charges, positive
and negative. However, there are some objects. Where the positive and negative charges are
equal to one another. In such cases, we say that the object is electrically
neutral. So, was the plastic comb initially electrically
neutral or electrically charged? Initially, the plastic comb was electrically
neutral. That means it had equal number of positive
and negative charges. Hence, it did not have the ability. To exert a force and attract the pieces of
paper. So, after rubbing the plastic comb on our
dry hair. Why was it able to attract the pieces of paper? I will tell you why. When we rubbed the plastic comb on our dry
hair. It gained an electric charge. Once it got electrically charged. It got the ability to exert a force on the
pieces of paper and attract them. This charge is called as static electricity. However, do you think, like a plastic comb. A metallic comb will also attract the pieces
of paper? No, you are wrong. A metallic comb will not attract the pieces
of paper like the plastic comb. Wondering why is that so? It is because plastic is not a good conductor
of electricity. It does not allow the electric charges. To flow through it onto the earth. As a result, the charges build in the plastic
comb. Making it electrically charged and enabling
it to attract the pieces of paper. However, metal is a good conductor of electricity. It does not let the charges build in it. It allows the electric charges to flow through
it onto the earth. Thus, not allowing the metallic comb to get
electrically charged. As a result, the metallic comb does not attract
the pieces of paper.