How to Build a Catapult

by thalia7

40K4010

Intro: How to Build a Catapult

Okay so in my 4th hour class, Conceptual Physics, our teacher instructed us to get into groups of three and build a catapult that would be able to launch a golf ball. After watching a catapult /trebuchet, it sort of inspired us and gave us an idea of what our teacher was looking for in our catapults. He had us to choose if we wanted to do a catapult or trebuchet, but we chose catapult, because a trebuchet seemed too complicated.

STEP 1: Getting Started...

Well of course you can't start building a catapult without equipment involved. You must grab enough wood for your catapult and tools; such as screws, hammers, handsaws, rulers, springs, etc. (you get the idea).
You need to know how big you want your catapult and how much wood you might need. You also might want to see how much weight your catapult might carry, if it's too big, you might want to get some assistance. This is where you use a ruler and begin to measure it. You must need a flat base that at least touches the ground. The measurements must be exact so no mistakes will interfer when you're putting it together.

STEP 2: Building, Screwing, & Hammering

Once you've got all the measurements correct and no mistakes are in the way, then you're ready to start screwing nails and building your catapult. Please do not do this alone, you might injure yourself (which is percisely why our Physics teacher wanted us to work in groups). Anyways, you must put the base together before getting a head start with the arm. Don't worry if your base isn't quite exactly touching the ground at an even position (trust me, ours wasn't either). If this happens, you must add some sort of support on the side that makes your catapult tilt. When your base is finally ready and supported, you may start with the arm. The arm however must have a good displacement so it could have some good and approving direction.

STEP 3: Putting It Together

This is where it gets tricky. Putting the two boards that will hold the arm in place (forgot what they're called) wasn't so easy. What I mean is, when screwing them in, it kind of tilts them out instead of straighten them out. The reason why you want the board supporters for the arm straight is because you want your arm to be right in the middle and have a good angled launch.
When we screwed in the screws to the boards, it caused our boards to tilt out and not be even. But we made some adjustments so it's all good. To make the hole in each of the board, you have to make the exact measurements. You could use a metal bar to hold the arm in place. If the bar is top small or the hole in the arm is too big, you could use duck tape so the arm won't move from side to side. Once you've finally adjusted the arm in a good angling postion, you must know where you'll include the springs that will help you pull the arm back and launch. Also you must be aware of  the velocity on the arm, you'd want your golf ball to go far off with super speed. 

STEP 4: Finishing: Time for Launching!!!

Once you've got your arm in place and the springs on properly, you could practice trying to swing the arm back. Oh wait! What's this? Seems that you don't have a stopper to stop the arm from messing up your launch. Please be sure to have a stopper to stop the arm when you launch.
You might also want to now the accerleration of the arm right? Well with our catapult, our acceleration was 308mph. It launched pretty far, but not so far. Our average speed wasn't high enough and the golf ball only went to 25 yards. The balanced force in the arm and having it to stop with the stopper, sort of got the golf ball to go pretty faraway distance, but not as far as we expected. But what amazed me was how the arm had a very instantaneous speed when it hit the stopper, it had such power and force; I was quite amazed with our catapult.
In the end, it turned out to having a great acceleration of the arm and we all had fun launching the golf balls in our school's field. 

9 Comments

theden1 9 years ago

I believe the reason you didn't achieve the distance you wanted is because the throw-arm was much too short. If you've got it accelerating to such a high velocity, it sounds like you had plenty of power, but didn't utilize the natural leveraging of that power that extending the arm would have brought. Your Catapault probably had the strength to throw bricks... But with an object as light as a golf ball, extending the arm and getting much more distance would have been easy. :)

goatdriver1957 12 years ago

As I view this pic, runs chills down my spin. DO NOT EVER PLACE ONE"S HAND in front of a power drill controlled by another operator. What ever that is being achieved can be done with out getting the hands in the middle of the action. Take a few more moments and figure it out to not jeopardize one safety.
Be safe and go home to mama as well as you were when she saw you last.

In high school my wood shop teacher had only one arm and when he spoke of safety about/around high speed cutting tools, everyone listen and it stuck. No, he didn't lose the arm in a shop event, lost during the war but some reason it meant more due to he had to function missing a limb.

overblast 13 years ago

If I used this to launch a pile of snowballs at my neighbor's snowfort, would it hurt if it hit them, or cause damage to their car or house?

ikeike40 13 years ago

how far does it throw?

nutsandbolts_64 14 years ago

 I'm gonna have to say your catapult has better size to range ratio than mine. Try prefabricating the catapult.

ungaru 14 years ago

 the reason why your golf ball didnt go so far is that your arm was pretty short;
using a longer arm (of course not a huge one) would provide the catapult with a massive amount of force(you could even double that 25 yard distance)

thalia7 14 years ago

yea...we were alittle short on wood so we were stuck with a small arm
but thanks for telling me. I somehow had a feeling it wasn't going to go far...but it's all good I guess.