Think about the perfect tree house.  It sits high up in the branches of a redwood tree, the tallest tree in the world.  Don't worry - you don't have to climb all the way up there.  There is an elevator system with a pulley that makes it very easy for you to hoist yourself to the top.  Up in the tree house, you have all the nice things that people have in their homes: a refrigerator, a television, and a secret trap door for tossing out bad guys and banana peels.  When you're all done enjoying your home in a tree, you get to ride a twisty slide all the way to the bottom!  Wheeeeeeee.  Doesn't that sound fun?  First, let's see if we can really build it.  To do this, we'll have to try thinking like an engineer. Being an engineer is all about bringing the ideas in your head out into the real world.  

In the make-believe world of ideas, there are no rules. You can do anything you want! (See our tree house example above.) To be an engineer, however, you have to follow a set of rules. This is why it's always good to lay things out with a clear head before you start building. A design is a plan for how to build something.  If we think with our real-world brains, we might have to abandon some of our ideas for the ideal tree house, like the elevator, the slide, and the redwood tree, which itself would be too tall to really be able to use as a place for our project. Sigh.

Before we build, we need to design!

cardoso/Flickr.com

Let's go back to the beginning, shall we?  Before any engineer moves farther than the brainstorm and idea stages, she needs to ask some important questions.  What is she going to build, why is she going to build it, and for whom is she building it? Having a clear answer to these three questions will help her figure out what to do as she moves through this from start to finish. In engineering, a need is a reason why you are building something. Engineers work hard to make sure they understand the problem so that they can build something that works best for what people need. This is true with people who build websites as much as it's true for people who build bridges, even though it takes two extremely different kinds of engineers to do those jobs. Does anyone really need a tree house?  Likely not.  But let's say that there is a need, for the sake of this example. Perhaps you have been called on by the government of a place where a tree house would give a safe place for people to go because there are dangerous wild animals around that can't climb trees or fly! Now we have a beginning and a place to start.

Let's gather more information. We want people to be safe while up in this tree house; falling from high places can be very dangerous! Criteria are principles to follow as you build something to make sure it is going to work the way you want it to. In other words, what will it look like and how will it work? You have to think about things like shape, size, weight, speed, and how easy it might be to make. 

Does anyone really NEED a tree house? Probably not. Are they pretty cool? Definitely.

Jennifer C./Flickr.com

Before you get carried away with your design, remember that you are building this tree house for someone with a need. We want the people who depend on this tree house to be a safe place to get away from harm, so we have some things we need to think of as we design and build the house. Constraints are limits to what you can do as you build something. Some common ones are cost, time, place, and how much you know.

All right, now you can start designing.  It's fun to think about wacky ideas, like a tree house in a redwood, but when it comes to real engineering, you have to take some steps.  First, you have to make sure there is a need for your plan. Then you must make yourself aware of your criteria, or what specific needs have to be met once it's built. Finally, you need to know your constraints!  What are you up against?  What materials will you need?  How much will it cost? Where is this tree? If you do these things, you just might bring a tree house--a real tree house--into the real world.

Think this would be strong enough to hold out house?

Rhian/Flickr.com