The difference between Internal Resistance and ohm's law is that ohm's law is a mathematical equation that can be used to calculate the voltage across an object and the current flowing through it, while Internal Resistance is a mathematical equation that can be used to calculate the resistance of an object in motion. Internal Resistance is caused by heat loss, friction, and other processes which act to slow down or stop the movement. Internal Resistance Formula is often used in engineering applications when designing engines and powertrains for cars or trucks, but it can also be applied in many other situations!