The poor performance of steam engines prompted Joule to carry out his research. page 2 of 10

Why was James Joule's work important to industry in Manchester?

Factory owners in the 19th century were very concerned with efficiency - how to produce more products for less work. Joule's experiments helped the manufacturers of steam engines and electric motors improve the performance of both by getting them to understand what was happening inside the machines. He established that electric motors were even less efficient than steam engines - 'the comparison is so very unfavourable that I confess I almost despair'.

He determined this through a series of experiments that looked at the relationship between wasted mechanical work and the energy of molecular motion or friction.