Work is a fundamental part of every person’s life. It’s how we earn a living, support our families, pay the bills and make a contribution to society. It’s also how we gain skills, knowledge and experiences that help us through the ups and downs of life.
It’s easy to see work changing other people – but it changes us, too. Think about the time, energy and relationships you put into your job and consider the ways it’s changed who you are: the wisdom you’ve gained, the mentors you’ve encountered, the positions that forced you to stretch and grow. Work can even give you a sense of purpose and meaning in your life.
Despite its importance, our concept of work is not always well understood. In particular, some things we might think of as hard work do not count as such in the scientific definition: for something to be considered “work” in physics, there must be a force exerted on an object and the object must have displacement (or motion). This means that things like a person carrying a heavy briefcase or swinging a weight around a circle are not actually “work” in the sense of transferring energy from one place to another, even though you may have been exhausted after doing them!
The SI unit for work is the joule, named after 19th-century English physicist James Prescott Joule. Other units include newton-metre, erg, watt hour and kilocalorie hour. Since work is a form of energy, it has the same physical dimensions as heat: it can be measured in joules per second or kilograms per square metre.
While there are many examples of work in everyday life, there are three situations when it is said that no work has been done:
When the magnitude of a force and its displacement have identical directions, then work is zero. When the direction of a force is aligned with the direction of displacement, then work is positive. Otherwise, it is negative.
An example of work is a batsman hitting a ball. This transfers a large amount of energy from the batter’s body to the ball, which moves away from the batsman.
Other examples include a car engine working to push a vehicle, a coolie carrying baggage up or down the steps of a railway station, and a cyclist riding a bicycle. These activities transfer energy to the objects that are displaced, which is what makes work happen. This also explains why you get tired after carrying a heavy briefcase or lifting luggage up and down stairs – your muscles are doing work. However, when a force is applied to an object and there is no displacement, it does no work. For instance, when a person holds a briefcase against the wall, or when a book falls off a shelf and lands on the ground. In these cases, there is a force and there is motion, but no work is done.