Pressure causes item to get hot (to the extreme being enough pressure creating a star).
But if heat is essentially the movement of atoms, why does more pressure cause more heat?
Ie. The focused pressure of an ice skate blade makes the ice under it to melt.
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When you hit a tennis ball with a racquet, you increase its speed. Similarly with a gas, if you compress it in a cylinder with a piston, say, the moving piston hits the molecules and increases their speeds. But it’s the speed of these molecules which defines their temperature: higher speeds = higher temperature. In the process the pressure is also increased, as there is less space for the same quantity of gas.
A less microscopic view is that by moving the piston against the gas pressure you expend some work = add energy to the gas = make it hotter. That’s conservation of energy.
When a gas cloud becomes a star, the incoming gas falls towards the center of gravity of the star. That is gravitational energy is converted to heat when the gas is compressed under its own weight, until fusion reactions set in and stop the condensation by generating heat, so also pressure which tends to fling the gas away. And you get an equilibrium between gravitational attraction and fusion generated pressure.
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