I'm not getting the definition of a joule. From the definitions I've read if I apply one newton of force to any object, now matter how heavy/ how much mass it has, over one metre in a single direction then I've done 1 joule of work.
a unit of work or energy equal to the work done by a force of one
newton acting through a distance of one meterA unit of energy equal to the work done when a force of one newton
acts through a distance of one meter.equal to the work done by a force of one newton when its point of
application moves through a distance of one meter in the direction of
the force:
So a force of one newton pushing on an object 1 kg heavy over one metre is 1 joule of work done, and a force of one newton pushing on an object 1000 kg heavy over one metre is 1 joule of work done? How is it the same amount of work done if I have to be pushing on that 1000 kg object a lot longer than the 1 kg object to move it over a metre?
Best Answer
Just because it takes more time doesn't mean more energy is spent. Think of gravity. It is constantly pulling in the book on the shelf - but no energy is spent, no work is done.
Only when the book falls is work done by pulling it further down. But it doesn't matter if the book started from rest and now falls while slowly speeding up, or if the book was thrown down with high initial speed so that it reaches the ground much faster - in both cases gravity did the same amount of work, spent the same amount of energy.
The duration that the force acts over has no influence on the energy being spent on the object, the work that is being done.
But you might still object to this answer. It does feel tougher to push on something over a longer time. You can clearly feel more energy being spent. And you are absolutely right. But this is of another reason: this is due to our inefficient human bodies and not due to more energy being given to the pushed object.
Our human bodies spend energy just to produce a force. So pushing for a longer time does correspond to more energy being spent. But all that extra energy is not spent as work on the object, it is just spent on compressing and elongating muscle fibres, on increasing heart rate and respiration, on adrenalin flows and circulation etc. Also a lot is wasted as heat. Of this reason it is unwise to rely on the human feeling when we are talking about energy usage in science. We are too darn inefficient and so much is going on beneath our surfaces for us to be relied upon.