RSS
Having an egg drop is like having your own egglympics. It will stretch your friends minds to think in new ways, bringing about a revolution in advanced thought... what I mean is that it's fun to break stuff.
It's best to use what you've got around... only have a weight limit if you have a scale. To make it harder, limit materials and time. Giving out 12 straws and 60 cm of tape is hard.
Paula Kieko helped out with the math and physics. The easiest thing to figure out is the speed of the egg at the time of impact.
In this example we are dropping the egg from the height of 10 meters.
Watch the video and make sure to download the pdf to get all the juicy details. Or subscribe in itunes and it will be downloaded automatically for you! - PDF Link
The top equation--the one with the v_0 term in it--is wrong, and I can't figure out where you got it. Fortunately, the initial velocity is zero and the incorrect term drops out, so your final answer is OK.
But what was the point of calculating the final velocity of the egg, anyway? The purpose of these devices is to dissipate the kinetic energy that the device attains during the fall by having the pieces stretch and bend and break. Calculating that energy is easy enough, but there's no point to it unless you're also going to calculate the energy absorbed by, for example, the breaking popsicle sticks and the stretching nylons.
Reply to this comment
DrDrang -- I've seen that first equation, except that that V_0 should be squared.
I think the reason for calculating the final velocity was just to spread knowledge :P So I could explain to the landlord why I'm dropping eggs off the top of his building -- or for younger kids to give a good explanation on why mom's flower garden now has peanut better and eggs :P
I don't think it would be very easy to calculate how much energy goes into a Popsicle stick. What is Young's Modulus for wood :P
Reply to this comment
I was about to comment on the equation, but you guys already got it covered. What would be cool is to see someone attach an accelerometer and post the data! Egg drops were by far my favorite physics project in middle school.
Reply to this comment
DrDrang, you're totally right!
We rewrote that paper so many times and I just didn't look closely enough. So, yes, V_o is supposed to be squared, but because we were dropping it (instead of throwing), it would still be zero. And I was debating whether to mention energy, but the introduction would be pretty lengthy... it's an exciting topic and I'd get carried away.
Oh goodness, having an accelerometer would be pretty fun! Though, with a few simple calcutations, we could easily find the acceleration at each point. We could even tape it, put it in a program and plot it! oh, the possiblities.
Reply to this comment
zmoney, instead of an accelerometer..... strain gauges :P Find out how much deflection it takes to crack an egg (well, a sample of eggs). Then drop with a strain gauge on and see how the egg shell moves :)
I suspect the shell can move more than one would think -- does anyone have high speed video of an egg falling unprotected?
Reply to this comment
trebuchet03,
If memory serves, Young's modulus for wood is in the neighborhood of 1-2 million psi (with the grain), depending on species and moisture content. But most of the energy dissipation will come with splintering, not elastic deformation.
I wasn't seriously suggesting that the calculations be made, but if you're going to be calculating anything, it should be energy.
As for strain gauges, good luck! If you want to figure out how much an egg shell deforms before cracking, I'd suggest a static test with a dial indicator.
Reply to this comment
I'm a physics teacher, and we just did our egg drops right before Christmas break while we were talking about momentum. We calculated how fast they would be traveling as a tie-in to previous units when we did kinematic equations. By the way, the first commenter was correct, the equation shown above is missing a square on the V_0 term. (Dimensional analysis people!)
We didn't talk about energy (because we hadn't done that unit yet) so we told our kids that the way to make your egg survive was to manipulate Impluse, which is the numerical value for change in momentum. All of their eggs had the same change in momentum (eggs roughly the same mass and the speed should be the same when reaching the ground), and since impulse is Force times Time, if you increase the TIME it takes the egg to stop moving when it hits the ground, you must decrease the FORCE, thereby safely landing your egg.
We did not let our kids use parachutes or any kind of air resistance to slow the egg's decent because then the impulse of hitting the ground would be less than the other students. Our successful entries included eggs inside of loaves of bread, eggs inside of PB jars (although you have to be careful of allergies) and marshmallow fluff jars, and one egg attached to two sides of a larg cardboard box by rubber bands and was able to oscillate without smashing into the sides.
Reply to this comment
how do you make an egg contraption with a way to be able to see the egg or take it out and see it after the drop... with these things:
80 popsicle sticks, 10 of which have notches in them
10 coffee straws
2 feet of string
1 paper bag
2 rubber bands
2 ties (i dont know the right term for it...)
2 paper clips
and lots of hot glue
cutting up the popsicle sticks and drilling them etc.. is aloud
Reply to this comment