In physics, work is energy that is transferred from or to an object through the application of pressure or a change in momentum. In its most basic form, it can be represent as the product of momentum and force. Put simply, the more work you exert on an object, the greater the amount of energy you need to move the object in the first place. The amount of energy needed to move the object depends upon many factors, including how heavy the object is and what kind of motion it exhibits.
One way to understand how much energy is needed to move an object is to consider how much work has to be done in order for you to get to a particular location. For instance, if you are at the International Airport in Chicago, you have to get off the plane and walk to the baggage claim area before getting your luggage weighed. Once you have weighed your luggage, you must climb some stairs, use a ramp, and get to the baggage belts where you have to manually carry your belongings onto the conveyor belt. Without this work done, you would not get to the baggage claim area and your luggage would not reach the scale where you will pay the weighed amount and be given your ticket.
Work done in this example is not necessarily hard labor. The amount of energy needed to do it all is only a tiny fraction of the total energy required to push or pull an object. This phenomenon is called mechanical energy. Simply put, mechanical energy is the work done over a period of time. It is measured in Watts (Watts is the amount of power measured in British thermal units).
Put another way, mechanical energy is the amount of energy needed to make an event happen. For instance, the oil pump in your car pumps up and compresses air to move the engine to work. The amount of work done by the oil pump depends on a number of factors like the displacement of the air in the tank, the distance between the piston and the cylinder, and the speed of the moving air. The net effect is that the oil pump works over time to produce a net force on the object.
Now let’s say that you are standing on a level ground, with nothing on your feet but your hands (with which you have to keep yourself steady), and you have a stick in your hand with a weight resting on top of it. You can easily manipulate the stick and increase or decrease the amount of energy it requires to do its job. To do this, you must have a working knowledge of how the law of conservation of energy describes motion. The law of conservation of energy tells us that the total amount of motion (the sum of the total energy required to change one point in an object from a higher to a lower temperature, for instance, and the change in temperature from touching a level ground to touching a different level ground) is conserved or will never change.
We know from the previous example that there is a net force on the object because there is a change in temperature as a result of the movement of the object. Therefore, we know that the total energy required to do the work is equal to the total energy required to make the same change in temperature. This is known as the dynamic force. On the other hand, there is also a static force. This is called the kinetic force, since it changes only due to the action of the body attached to the object. The final form of the law of conservation of energy is referred to as the equilibrium law, because it states that the total amount of energy that is present at a given time will always be the same, no matter what changes take place.