why heating of substances is done from bottom?

Answer 1

Because heat rises.

Answer 2

Generally when a substance is heated, it expands; thus the same weight of substance takes up a greater space, it becomes less dense and rises above the denser, cooler material above it. (as in a hot air balloon where the hot air inside the balloon is less dense and therefore lighter than the surrounding air outside the balloon). So, in order to heat a substance evenly it is more efficient to heat it from the bottom. The warmer part at the bottom will rise allowing the cooler part to sink to the bottom and this will continue to cycle until all the substance reaches the desired temperature.

Answer 3

1.) Most substances are lighter when heated, because the molecules expand. Therefore, heating from the bottom is most efficient, because it encourages the heated molecules on the bottom to rise - this helps transfer the heat more quickly.
2.) Generally, it's simpler and safer to heat from the bottom.
3.) That said, heating does not have to be done from the bottom. Many ovens have a heating coil on the top and the bottom, and a lot of cooking done in a fire is done by putting hot coils on top of the pot's lid.

Answer 4

This is not entirely true....for instance, in chemical industry, there are reactors (the pots that hold the substances and in which the reactions take place) that are heated from the outside, almost all around, with some warm agent (like water vapors or ....)
However, in your home, the most simple way to heat something is to put it on the fire....and the fire it's easier to keep it burning if it comes from downside....(have you ever tried to hold a candle upside down?)
Apart from that, the heat tends to go up, so if you placed the heating source upside the pot containing the substance that you want to heat, it would probably take a longer time to warm it....

Answer 5

Heating a substance from bottom requires minimum energy. Heat waves are lighter than air and so tend to go up ,naturally heating the things in their way. If one has to heat up the substance from top (as in the case of baking bread) it will need lot of energy and arrangement for directing the heat downward.

Answer 6

As there is gravity feild exist, all atoms and particles acts towards the bottom of the vessel and as fire is made at down it will spread and it has more contact area, so rate of heating will be more and it will assist reduction in time and energy. In any other position we perform heating it would a great loss in energy and heat.

Answer 7

Because of the fact the heat RISES.

Answer 8

First of all, heat rises. Second of all, if you blow the fire from upwards it would mean you need to have the container upside down (which is an inconvenience). It's just stupid to do otherwise.

Answer 9

cos' heat need to rise and escape. if it is trapped (say by heating from top) it might expand and explode

Answer 10

during the stone age the cave man would make fire to cook and would burn their hands since they make fire from the top. that gave them a lesson and taught the following generations up to our time. and now learn it from us, fire rises so you light from the bottom.