How do I find the dampening effect of a spring?Is there 1?

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Assasinof6
Posts: 22
Joined: Sun May 09, 2010 1:37 pm UTC

How do I find the dampening effect of a spring?Is there 1?

Postby Assasinof6 » Fri Jul 16, 2010 10:47 pm UTC

I am doing an egg dropper assignment as part of a project, and I was going to incorporate springs into the design to lessen the effects of the impact.
I am required to write a report, and as such, I need to discover how much force the egg will experience.
I need, however, to learn how to FIND the dampening effect of springs. Is there a simple formula I could use to discover the energy output of the spring?
For instance, if a 1.0 kg box is dropped onto a spring attached to the top of a 0.5 kg box, how much force does the box feel as a result? I'm looking for formulae in the answers, such as:
Fe = Fa / (M2 + M1), where Fe is the experienced force (on the o.5 kg box), Fa is the applied force, and M2 and M1 are the box masses.
THAT IS NOT THE CORRECT FORMULA.
I am ASKING for the formula, and an explanation.
Thank you in advance!
I see.
What?
That you don't.

Carnildo
Posts: 2023
Joined: Fri Jul 18, 2008 8:43 am UTC

Re: How do I find the dampening effect of a spring?Is there

Postby Carnildo » Sat Jul 17, 2010 2:35 am UTC

There are so many wrong assumptions in your post that I don't know where to begin.

The key to having an egg survive an egg-drop is to minimize the impulse experienced by the egg. Parachutes and other drag-based methods do this by minimizing the impact speed. Deformation methods such as springs and crumple zones do this by increasing the time and distance over which the egg's velocity is reduced to 0.

The keys to using a spring in an egg-drop are:
1) Find the maximum force that can be applied to an egg without it cracking.
2) Calculate the velocity of the egg at impact (since you're not using a drag-increasing device, this can be approximated using the standard gravitational acceleration equation).
3) Select a spring with a stiff enough spring constant that it can bring the egg to a stop without bottoming out, but low enough that the maximum force won't exceed what the egg can survive. It also needs a high enough damping factor that it won't launch the egg back into the air -- after the first impact, the system becomes chaotic, and it will be difficult to ensure that further impacts don't break the egg.
4) Ensure the device hits spring-first.

Assasinof6
Posts: 22
Joined: Sun May 09, 2010 1:37 pm UTC

Re: How do I find the dampening effect of a spring?Is there

Postby Assasinof6 » Sat Jul 17, 2010 11:37 am UTC

Ok, thanks for helping me out. I am going to use a parachute, elastic bands, springs, and an aluminum crumple zone.

Here is a terrible MS paint so you will see what I am trying to accomplish.
Image
If the image isn't visible click the link below.

http://s897.photobucket.com/albums/ac176/Assasinof6/Terrible%20MS%20Paints/?action=view&current=Eggdrop.png

The weird springy things underneath the second box are... springs.

Thanks again!
I see.
What?
That you don't.


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