Work is not that hard… it’s force that can be difficult. Imagine getting up a 10-step flight of stairs without a set of stairs. Your legs don’t have the strength or force for you to jump up… you’d have to climb up or find a ladder or a rope. The stairs allow you to, slowly but surely, lift yourself from the bottom to the top. Now imagine you are riding your bike and a friend of yours is running beside you.
Who’s got the tougher job? Your friend, right? You could go for many miles on your bike but your friend will tire out after only a few miles. The bike is easier (requires less force) to do as much work as the runner has to do. Now here’s an important point, you and your friend do about the same amount of work.
You also do the same amount of work when you go up the stairs versus climbing up the rope. The work is the same, but the force needed to make it happen is much different. Don’t worry if that doesn’t make sense now. As we move forward, it will become clearer. Before we start solving physics problems, we first have to accurately define a couple of terms we’re going to be using a lot that you might already have a different definition for.
Here are three concepts we’re going to be working with in this section:
- Work
- Energy
- Power
Energy is the ability to do work. Work is done on an object when a force acts on it so the object moves somewhere. It can be a large or small displacement, but as long as it’s not in its original position when it’s done, work is said to be done on the object. An example of work is when an apple falls off the tree and hits the ground. The apple falls because the gravitational force is acting on it, and it went from the tree to the ground. If you carry a heavy box up a flight of stairs, you are doing work on the box.
An example of what is not work is if you push really hard against a brick wall. The wall didn’t go anywhere, so you didn’t do any work at all (even though your muscles may not agree!). Mathematically, work is a vector, and is defined as the force multiplied by the distance like this: W = F d
If there’s an angle between the force and displacement vectors, then you’ll need to also multiply by the cosine of the angle between the two vectors. This is an important concept: Notice that the force has to cause the displacement. If you’re carrying a heavy box across the room (no stairs) at a constant speed, then you are not doing work on the box.
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