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Why does cold air make hot air move in physics?

Brandon Scott

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Mindee Nelson on May 15, 2019

In reality, the cold air & hot air to circulate. Imagine 3 laser beams are focused to converge at a single point in a typical room with normal air temperature. When the laser is switched on, the rays converge and energy to the air molecules that are in the area of convergence. As the photons of light collide with the air molecules, the air molecules absorb energy, vibrate/oscillate, & collide with other nearby molecules of air very quickly. This high kinetic energy state is what we call heat (i.e., energy in the form of heat). Because the heated molecules collide with other molecules, the distance between the heats the molecules increases. This results in a lower density of the region (where heated air molecules) within a higher density zone (where the cold air molecules are). The gravitational pull of each of the molecules equally, however, the more dense that fresh air is pulled down to displace the warmer less dense air. To visualize this more easily, imagine a drop of oil is injected into the center of a cup of water and the oil is less dense than water. Finally, the force of gravity pull the more dense the molecules of water below the oil molecules. As the more dense water displaces the less dense oil, the displaced oil moves up to the surface. Original poster of the Answer: -------------------------- Technically it is the hot air that makes the cold air moves in, however, that is the wrong terminology. The hot air rises in fluids due to convection currents. When the air is heated it expands (as the particles get more kinetic energy) and, therefore, becomes less dense. It will be, then, instead of forcing the more dense the air. The more dense the air, it warms and becomes less dense and the cycle continues. A real-life scenario of this is the reason why it is hotter in the sauna, the most high sit.

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