How Can I Create a Portable Egg Catcher That Meets Strict Requirements?

[phoenix3997]

I must drop an egg from 2m, 6m, and 8m without cracking it.
The egg cannot be attached to anything or encase in anything. I must drop just a plain egg into something to catch it.
The "catcher" must not be taller than 5 cm. , and the catching area must be less than 2000 cm^2.
The device must be portable and moving it shouldn't require any rebuilding.
The project cannot be messy.
The lighter the project the higher the score.
So far I have tried a bag of rice krispies and memory foam from 10 ft. but both have failed. The hardest part is extending the time of collision because I only have 5 cm. to work with.

 

[jtbell]

Try a Google search for "egg drop project."

 

[jim mcnamara]

Moved from General Physics... no homework template.

 

[phoenix3997]

Try a Google search for "egg drop project."

I tried but most are encasing the egg. I need to catch an egg with nothing attached to it.

 

[anorlunda]

https://www.youtube.com/results?search_query=egg+catcher+project+ideas

 

[phoenix3997]

https://www.youtube.com/results?search_query=egg+catcher+project+ideas

The first video was okay but the devices were above 5 cm. The rest of the videos were eggs dropped while inside something not onto something.

 

[Swamp Thing]

The permitted area of 2000 sq cm could be a possible clue. That allows you to make something like a life net, also known as a Browder Life Safety Net or jumping sheet about 25 cm in radius. You can stretch a rubber sheet on a ring (tennis racqet?), and my intuition (not worth much) says it should work.

Edit: are you allowed to deploy your skills to catch it again and again if it bounces a couple of times?

 

[Swamp Thing]

In prev. post, replace the ring with a 5 cm deep circular pan. Fill the bottom 1 cm with cotton or whatever you think is the best damping material. Stretch rubber sheet across top. Optimize tension of the sheet and thickness of cotton layer so the egg is pretty slow by the time it reaches the damper. No smash, no bounce.

Consider punching a lot of very small holes in the bottom of the pan - they will add some viscous damping when the air tries to rush out through them.

I'm sure you have already decided to do all your trials with a "pilot egg" of the right shape and weight, that won't actually break.

 

[phoenix3997]

In prev. post, replace the ring with a 5 cm deep circular pan. Fill the bottom 1 cm with cotton or whatever you think is the best damping material. Stretch rubber sheet across top. Optimize tension of the sheet and thickness of cotton layer so the egg is pretty slow by the time it reaches the damper. No smash, no bounce.

Consider punching a lot of very small holes in the bottom of the pan - they will add some viscous damping when the air tries to rush out through them.

I'm sure you have already decided to do all your trials with a "pilot egg" of the right shape and weight, that won't actually break.

Thank you. I will start working on that.

 

[phoenix3997]

The permitted area of 2000 sq cm could be a possible clue. That allows you to make something like a life net, also known as a Browder Life Safety Net or jumping sheet about 25 cm in radius. You can stretch a rubber sheet on a ring (tennis racqet?), and my intuition (not worth much) says it should work.

Edit: are you allowed to deploy your skills to catch it again and again if it bounces a couple of times?

The permitted area of 2000 sq cm could be a possible clue. That allows you to make something like a life net, also known as a Browder Life Safety Net or jumping sheet about 25 cm in radius. You can stretch a rubber sheet on a ring (tennis racqet?), and my intuition (not worth much) says it should work.

Edit: are you allowed to deploy your skills to catch it again and again if it bounces a couple of times?

The egg shouldn't bounce out of the device but a little bounce is fine

 

[CWatters]

If the max height is 5cm then that determines the max stopping distance and the minimum deceleration.

Ideally you want a way to increase the stoping distance and reduce the deceleration. How about jets of air? Could you arrange for something like a leaf blower to make 50cm tall jets of air to catch and suspend the egg off the ground?

Edit: obviously a leaf blower would be too tall but perhaps some sort of compressed air or CO2 cylinder would fit?

 

[Swamp Thing]

50cm tall jets of air

You might need to hire a lawyer to justify this loophole. Is the jet of air a part of your apparatus? Physically, it is part of the stationary system and begins interacting with the falling system well above the 5 cm permitted height.

But me, I would give you lots of plus points for lateral thinking. And visually, it would be fabulous if you could end up with the egg hovering in the jet as in some of those Bernoulli devices. It would go viral on YouTube, for sure.

 

[Swamp Thing]

The egg shouldn't bounce out of the device but a little bounce is fine

I found this problem so interesting that my thoughts kept returning to it.

If we follow a system engineering approach, there are three elements to think about, and each can be addressed by a different component.

1. The rubber membrane uses elastic forces to decelerate the egg nearly to zero, and converts nearly all the KE into PE. It achieves this without concentrating the force too much at any point on the egg's surface.

2. The thin cotton layer just gives us a margin for error, cushioning out the residual velocity that might remain after the rubber membrane has removed most of the KE (This would be like dropping the egg onto the cotton from a few cm height). "Cushion" for error, ha ha.

3. Now to prevent rebound we add a third component -- a flap valve in the container's wall that will allow the air to exit fairly quickly. But as soon as the rebound begins, (i.e. the membrane starts converting PE into KE) the air tries to rush back into the container, but the valve closes. This slows down the rebound and the membrane slowly pulls upwards as the air oozes in. The membrane's PE is converted into heat through viscous friction.

 

[Swamp Thing]

A totally different approach would be:

To satisfy the no-splash, no-mess rule, we seal the top of the pan with a thin polythene sheet that is taped LOOSELY over it. The sheet is only meant to satisfy the no-mess rule. It should be loose enough that the egg can descend say 4 cm into the pan, which is 5 cm deep.

Inside the pan we have butter, jam, honey, oil or maybe just water.

But this device would lose a lot of points on account of weight.

Question: would an egg crack if it was dropped into water from 8 m?

Edit : It could crack, unfortunately.

 

[kuruman]

Have you considered a spandex safety net?

 

[CWatters]

With a maximum stopping distance of just 5cm the deceleration forces will be quite high.

a = - g h/s

where

a is the deceleration
h is the drop height
s is the stopping distance

so with h = 8000 cm and s = 5cm

a = -1600g

and realistically I think it could easily be double that.

even at 2m you get a = -400g

Google suggests 63 grams for the mass of an egg. If we assume a constant force Newton puts it at 1600*0.063 = 100N. That's like a 10kg object compressing the catcher.

Perhaps double check the rules say 5cm?

 

[Swamp Thing]

That's like a 10kg object compressing the catcher.

It does seem like a hopeless quest when we neglect the air resistance / terminal velocity thing. But wait...!

Let's look at it this way:
[1] If we pressed the egg into a really tightly stretched membrane with a force of 10 kg, it is likely to crack, even if we distribute the force uniformly over the top surface of the egg. But if the force on top is fairly uniformly distributed, the cracking threshold is likely to be still pretty high -- I'd say a couple of kilograms, because the lower surface is cradled nicely to distribute the balancing upward force.

[2] However, the deceleration force(s) don't act on the top surface -- what is decelerating is mostly the white and the yolk, and by Pascal's principle they would produce a pressure spike all over the inside surface of the lower part of the shell. Once we take this into account, what can crack the shell is only the small non-uniformities in net force caused by the behavior of the membrane when it tries to stretch and match the shape of the egg. That is, if the membrane allows some parts of the yolk to decelerate more slowly than others. I think this gives us a significant margin in our favor.

 

[Swamp Thing]

Bump to flag a new image added in old post.