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1) They can bend sideways in summer due to linear expansion of the steel. Hence, a small gap is left between the rails at the time of laying them. This is because rails expand in summer due to increase in temperature. The gap is provided to allow this expansion.
2) hot air balloons achieve flight because of hot air. As the air inside the balloon (or the envelope) heats up, it becomes less dense than the air outside the envelope. This causes the balloon to rise.
3) A hotter substance cools faster because there are many substances are cooler than it and it transfers heat to all those substances. Therefore, a hotter substance cools faster.
4) Stainless steel is generally provided with a copper bottom because copper is a very good conductor of heat and electricity. Thus, it helps in directing the heat evenly throughout the utensil, and heats the steel pans faster. So cooking process will take less time with these copper coated steel pans.
5) In places of hot climate, it is advised that the outer walls of house be painted white because white colour does not absorb any heat radiation from the sun which keep inside cool even if there is hot climate outside the house.