I recently took on a part time job teaching science to K-7th graders after school. Today I’m sharing with you one of the activities I did with the fourth through seventh graders: Giant Slingshots. Summer is coming and soon-to-be-school-free kids will be scrounging around looking for something to do. Lest they decide to jump off the roof with bed sheets as parachutes for lack of any other suitable activity (true story), build them a slingshot.
I built this one in under an hour. It’s not hi-tech, but it doesn’t need to be. The students were completely captivated by the idea of being The One who slung a ball the farthest down the field. As a result they listened intently to my (short) lectures on trajectory, velocity, force, mass, and aerodynamics. I set it up on the grassy field behind the school, and ended up with every kid on the playground standing in line, waiting for a turn, and offering advice on how to get the next ball to go just a little bit further.
Here’s what you’ll need:
- Two 10-foot long 2x4s
- One 6-foot long 2×4 (you’ll have a little bit left over at the end).
- Six feet of latex tubing.
- Some tennis balls—the kind that come in a little mesh bag—you’ll need the mesh bag.
- A little bit of twine—say two feet.
- Ten screws long enough to go through a 2×4—say 3 or 3 1/2 inches long.
- Some weights—logs, bricks, or whatever other heavy materials are lying around.
- A circular saw or handsaw.
- A drill and two bits: one of a slightly smaller diameter than the 3 inch screws, and one with a Phillips head.
All of these items can be found at your local giant hardware store. They’ll be confused when you ask for the tubing, but it is there with all the other types of tubing (in my store on the very top shelf).
And here’s what you do:
Step one: Cut one of the 10-feet long 2x4s in half so that you have two 5-foot long sections. Cut another ten foot long 2×4 into two 4-foot lengths (you’ll have 2 feet left over that you’ll need). An cut the third 2×4 into one 3-foot section and one 2-foot section). You’ll have one foot left over.
Step two: Connect the 2-foot sections to the ends of two of the 5-foot lengths, so that each forms a T. Place the 2-foot board so that it is flat against the end of the 5-foot board. These are the ‘feet’. Two screws in the base should hold them on.
Step three: Connect the two 4-foot lengths to the now T-shaped pieces… about 18 inches up from the T-junction. These should be connected at between a 45° and a 60° angle. Again, you’ll need two screws per side to keep the piece from swiveling. These are the braces that extend out the back, so you want them angled in such a way that when the post (the 5-foot piece) is standing straight up, one end of the 4-foot length touches the ground.
Step four: Connect the two legs that you’ve just created to each other, using the 3-foot section of 2×4. Two screws per side.
Step five: Cut the tubing in half, so you have two 3-foot lengths. Tie each to the top of a 2×4 leg. I used a couple of half-hitches. Tie the other end of each piece of tubing to a piece of twine, also using a square knot. Cut open the tennis ball mesh bag and fasten it between the two pieces of twine to create a ‘basket’.
Step six: Put weights on the T-pieces on the ground to hold them down. Alternatively and if you want something more permanent, bury those ‘feet’ in the ground. You’ll have to dig the angled supports in a bit too, to keep the posts upright.
Step seven: Insert a tennis ball in the basket, stretch, and release! You’ll have to practice where to hold the ball to get the best launch. We’ve launched tennis balls over 50 yards now…
To make it slightly inquiry based, I gave the kids a whole selection of different balls (tennis, nerf, softball, etc.). We weighed them and measured their diameter, and then compared the distance achieved with ball weight and diameter. I also attached a protractor to the side of one leg and asked them to determine which angle resulted in the maximum distance, holding all other variables constant (thus, they learned the word ‘variable’ and also one of the keys to a successful scientific experiment without even knowing they were *gasp!* learning.)
Cautionary note: I used light enough balls that having kids run around underneath to catch them was not a problem, and was half the fun for those waiting their turn (and for a ball). If you use softballs, beware the sting of catching one. Each kid was required to yell “heads up!” before firing (which they loved), and they couldn’t fire til everyone was paying attention (which was good for scientific observation too). One of your kids will eventually think to try water balloons… I can’t comment on this as we haven’t tried it yet (but it would be a great way to ‘mark’ where a ball landed if you’re measuring distance). We also thought of setting up cardboard boxes Angry Birds style to knock down, but didn’t have time. Also, helpful reader George points out that it is possible for these to backfire, and shoot the projectile at you instead of forward (not with as much force, but still unpleasant). I don’t have any personal experience with this so am not sure how it happens, but be aware that it can!