The close relation of work and heat

Work and heat are both measured in joules, and are considered different ways of transferring energy. They are found experimentally to be easily intercovertable. Consider the pistons and cylinders below:

We can perform work on the left piston to compress it. Or heat the gas on the right to increase the pressure, pushing the piston, hence performing work. You could even use some of the work gained from the expanding gas to push current through a resistor, producing heat, and that heat can be used to expand a gas... and so on.

Work is the transfer of energy which makes use of ordered motion. The ordered direction of a falling piston introduces random kinetic motion into the gas molecules. So the piston is doing work which is converted to heating the gas.

Heat is the transfer of energy which makes use of random motion. The expansion of a gas in the cylinder will convert the random motion of gas particles into the ordered upwards motion of the piston. So heat from the gas is transformed into work.

The ordered and random motion does not have to be kinetic. An electric current is considered to move in an ordered motion, so using energy to drive a current would be considered doing work.