What is horsepower?

Most of us have heard the term ‘horsepower’, but what exactly does it mean?

Way back in the Industrial Revolution, before combustion engines were invented, heavy-duty work was completed by work horses, so what a better way to measure the amount of work you needed to do than by the number of horses it would take to complete it?

BBC Earth Lab’s Greg Foot takes you through the historical significance and modern uses of the well-known expression.