Why exactly (on the level of particles interacting with each other) do things heat up with friction? E.g. airplane from friction with air. Also what is the difference between conduction and convection, they sound like the same thing only that its friction between a liquid/gas and a solid instead of a solid and a solid. In your answer note that I am a high school student so preferably take into account I don't have a knowledge of high level physics (as you can probs tell haha).
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$\begingroup$ Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. $\endgroup$– Community BotCommented Apr 22 at 2:06
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2 Answers
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Suppose we have an ideal gas at absolute zero. We know that at absolute zero the gas particles are motionless, so in the ground frame we observe a collection of stationary particles and the combined kinetic energy of the particles is zero.
Now imagine we have a plane flying through this gas with some velocity $v$. In the rest frame of the plane the gas particles are all approaching the plane with the same velocity $-v$:
Let's start by assuming there is no interaction between the plane and the gas, so the plane will pass through gas leaving it unchanged. Then after the plane has passed through the gas the particles still all have the same velocity $-v$, and that means in the ground frame their velocity is still zero i.e. their KE is still zero.
But this is clearly unrealistic as some gas particles will hit the plane and bounce off at random angles. We would get something like this:
After the plane has passed through the gas we expect the velocities of the gas particles would be changed so they are no longer all in the same direction and they no longer all have the same magnitude.
But this means that if you are observing from the ground then after the plane has passed through the gas the gas particles would no longer be stationary. They would be moving around with random velocities, and if you added up their kinetic energy you would find it is not zero.
Since energy is conserved the KE of the gas particles must have come from somewhere, and obviously it has come from the KE of the airplane. That means the plane has slowed down, and that means there is a frictional force (aerodynamic drag) acting on the plane, and the plane's engines have to do work to compensate for the energy lost to the gas particles. This the microscopic origin of the frictional force on the plane.
From the ground the temperature of the gas was originally zero and the gas particles were all motionless. But after the plane has passed through the gas particles are moving randomly, and the random motion of the gas particles is exactly what we mean by heat. So the temperature of the gas is now greater than zero. The end result is that the kinetic energy of the plane has been converted to heat in the gas.
answered Apr 22 at 7:51
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All materials are made up of atoms which have a positively charged nucleus and negatively charged electrons revolving around in orbits.
So the atom overall being a neutral entity does contain charged entities.
So when 2 substances come in contact these charged centres interact with each other applying attractive or repulsive or both forces and so there is a loss of energy in the form of heat.
These interaction forces are electromagnetic in nature. And frictional force also comes under this category. Frictional force is also a result of these interactions.
Friction in between the layers of a liquid or gas is termed as viscous force
