This is a simple one, but I think well worth it, and very cheap to make. For any of you taking Trigonometry or Physics this semester this actually might come in handy. You can use this to measure (with accurate results) the angles of elevation and depression. With these numbers you can then do lots of great things such as calculating the height of a building or a mountain (not as accurate, but close enough). I actually just used this little device to measure the height of the climbing wall at the gym in my workplace (that's right, my workplace has a climbing wall)!
Let's get started!
Step 1: What You'll Need
Step 2: Create the Plumb Bob
The sinker will act as a plumb bob. For those of you who don't know what a plumb bob is, here's a brief description: a piece of lead or some other weight attached to a line, used for determining perpendicularity. Basically it keeps the line always pointing straight down.
The first thing we want to do is tie a secure knot around the sinker. Take a gander at this wonderful ible created by adaviel on how to tie various knots if you're unsure on how to do this.
Step 3: Protractor Time
Now that we have our plumb bob we can attach the it to our protractor. You can do this by inserting the other end of your string or fishing line through the hole found where the x and y axis meet. Then tie a knot to secure it. Once you have tied your knots snip off the excess string with scissors.
For added strength feel free to add a drop of Gorilla Glue into that hole.
Step 4: Lasers Make Everything Better!
We have our protractor with the plumb bob. Now we need to add a sighting device. This can be done with a straw; however lasers are so much cooler, so I went ahead and added a laser to mine. The advantages of using a straw is the fact that lasers can't exactly sight in a mountain, range is the key player here. The disadvantage of a straw, it's not as accurate as the laser when it comes to shorter distances. For me, a laser was perfect for measuring the height of the climbing wall (70 ft.).
You can attach the laser or straw to the protractor with super glue if you wish to make it permanent. If not, tape should work just fine.
In the next step I'll go over using your new tool!
Step 5: How It's Done
So now you have your handy dandy Laser Mounted Plumb Protractor and you want to start calculating heights. Let's start with the height of your house.
1) From the wall measure the distance that you will be sighting from. Write this down as your base length.
2) Point the laser at the top of your roof taking note at which degree the line falls on.
3) You'll find the angle of elevation by taking the largest number on your protractor and subtracting 90 from that number. Write this down as your angle.
4) Now a little trig. If you have a calculator input the following calculation to find the height:
height = base length / cos(angle). So if your angle was 70, and your base length was 13 feet you're calculation will look like this: height = 13 / cos(70), which will give you a height of 36 feet, not including the height of your measurement.
5) You must take into consideration the height of the ground to the sight. You can keep it simple by first knowing the distance from the ground to your eyes and always keep your tool at eye length. So when you have this value you simply add that to your trig calculation.
Check out the picture if you need help understanding the concept.