Why doesn't the tawa handle burn your hand?
The tawa is hot enough to puff a roti. Your mother picks it up by the handle with a bare hand. Same tawa, same flame — and the handle is cool enough to hold.
Heat moves through a solid by being handed along. The tiny particles nearest the flame start jiggling hard, they bump the ones beside them, and the jiggling travels — like a bucket of water passed down a line of people.
Metal is very good at this. Wood is very bad at it —about a hundred times worse. So the jiggling races across the iron disc and then arrives at the wooden handle and almost stops.
Try it today
Stand a steel spoon and a wooden spoon in the same bowl of hot dal. Count slowly to twenty, then touch the top of each one.
Be honest about what happens: the wooden spoon does get warm, just far more slowly. Wood is a poor conductor, not a magic shield. If your child notices the wooden handle warming after a long time on the stove, they have noticed something true.
The word for it: conduction — heat travelling through a material by being passed from particle to particle.
Why does blowing on hot dal cool it down?
Everyone does it. Almost everyone explains it wrongly — including most adults, who will tell you that you are blowing cold air onto the food.
Your breath comes out at about 35°C. That is warmer than the room. So you are not cooling the dal by blowing cold air at it — there is no cold air involved.
What actually happens: hot dal is always losing a little water into the air, and that escaping water carries heat away with it. But the air sitting directly on the surface gets damp and warm, and once it is full, no more water can leave. Blowing sweeps that spent layer away and lets the process start again.
Try it today
Blow on a spoonful of hot dal. Then blow just as hard on a hot dry roti. The dal cools noticeably faster — because there is water leaving it, and hardly any leaving the roti.
Then ask why a wet cloth on the forehead cools a feverish child, and why a matka keeps water cold. Same answer, three places.
The word for it: evaporation — water leaving as vapour, and taking heat with it.
Why does the cooker whistle, and why is it faster?
Rajma in an open pot takes hours. In the cooker it is done in twenty minutes. The flame is the same size. Something else is going on.
Water has a stubborn rule: at normal pressure it boils at 100°C and then refuses to get any hotter. Turn the flame up and you do not get hotter water — you just get more steam. So an open pot of rajma is cooking at 100°C no matter how impatient you are.
Seal the pot and the steam cannot leave. The pressure inside climbs, and under that pressure water can reach around 120°C before it boils. Twenty degrees hotter cooks dramatically faster.
The whistle is the safety valve doing its job: when the pressure gets high enough, the weight lifts, a little steam escapes, and the weight drops back. It is not a timer, and it is not the food announcing that it is ready.
Watch, do not touch
This is the one question on this page with no experiment attached. Escaping steam is at 100°C or above and burns badly — worse than boiling water, because it dumps a great deal of heat as it turns back to liquid on the skin.
Watch the weight lift from across the kitchen. That is the whole demonstration, and it is enough.
The word for it: pressure — and the fact that it changes the temperature at which water boils.
Common questions
›Why does the tawa handle stay cool when the tawa is hot?
Because the handle is made of wood or plastic, and those materials pass heat along very badly. Metal passes heat from one tiny particle to the next quickly, so the whole metal disc gets hot. Wood does it about a hundred times more slowly, so almost nothing reaches your hand in the minutes the tawa is on the flame. The wooden handle does warm up eventually — it is a poor conductor, not a magic barrier.
›Does blowing on hot food actually cool it, or is that just a habit?
It genuinely works, but not for the reason most people assume. Your breath is around 35°C, so you are not blowing cold air onto the food. What you are doing is pushing away the layer of warm, damp air sitting on the surface. Once that layer is gone, more water can evaporate from the food, and evaporation takes heat away with it. That is why blowing works much better on wet dal than on a dry roti.
›Why does a pressure cooker cook food faster?
Because it lets water get hotter than it normally can. In an open pot, water boils at 100°C and refuses to get any hotter — extra heat just makes steam. A sealed cooker traps that steam, the pressure rises, and under pressure water can reach around 120°C before boiling. Food cooks faster at 120°C than at 100°C. The whistle is the weight lifting to let a little steam escape so the pressure does not keep climbing, not a signal that the food is done.
›What should I say if my child asks something I cannot answer?
Say you do not know, and find out together. A confident wrong answer is worse than an honest one, and children work out surprisingly early which adults are guessing. "Let us try it and see" also teaches the more valuable habit — that questions are things you investigate rather than things you look up in an adult.
More heat, in the kitchen
Once your child starts noticing, the questions keep coming. Why the steel glass feels colder than the wooden table when both are the same temperature. Why milk boils over but water does not. Those are coming to this page.
Meanwhile: the float-or-sink kitchen lab →