This experiment is for Advanced Students.There are several different ways of throwing objects. This is the only potato cannon we’ve found that does NOT use explosives, so you can be assured your kid will still have their face attached at the end of the day. (We’ll do more when we get to chemistry, so don’t worry!)
These nifty devices give off a satisfying *POP!!* when they fire and your backyard will look like an invasion of aliens from the French Fry planet when you’re done. Have your kids use a set of goggles and do all your experimenting outside.
Here’s what you need:
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- potatoes
- an acrylic tube (clear is best so you can see what’s happening inside!)
- wooden dowel
- washer (this is your ‘hand-saver’)
Where is the potential energy the greatest? How much energy did your spud have at this point? Hmmm… let’s see if we can get a few actual numbers with this experiment. In order to calculate potential energy at the highest point of travel, you’ll need to figure out how high it went.
Here are instructions for making your own height-gauge:
Once you get your height gauge working right, you’ll need to track your data. Start a log sheet in your journal and jot down the height for each launch. Let’s practice a sample calculation:
If you measured an angle of 30 degrees, and your spud landed 20 feet away, we can assume that the spud when highest right in the middle of its flight, which is halfway (10 feet). Use basic trigonometry to find the height 45 degrees up at a horizontal distance ten feet away to get:
height = h = (10′) * (tan 30) = 5.8 feet
(Convert this to meters by: (5.8 feet) * (12 inches/foot) / (39.97 inches/meter) = 1.8 meters)
I measured the mass of my spud to be 25 grams (which is 0.025 kg).
Now, let’s calculate the potential energy:
PE = mgh = (0.025 kg) * (1.8 meters) * (10 m/s2) = 0.44 Joules
How fast was the spud going before it smacked into the ground? Set PE = KE to solve for velocity:
mgh = 0.5 mv2 gives v = (2gh)1/2
Plug in your numbers to get:
v = [(2) * (10) * (1.8)]2 = 6 m/s (or about 20 feet per second). Cool!
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