### Author Topic: Spring mass question  (Read 3242 times)

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#### arixrobotics

• Full Member
• Posts: 119
##### Spring mass question
« on: August 30, 2008, 11:53:23 PM »
Hi all,

Can the smart mechanical engineers here help me with my homework please? I know this is not related to robots, but I need someone with good knowledge of mechanics.

So here's the problem;

I have a mass, and I mounted a spring below it for shock isolation. Then, I released the whole system from a certain height. Assume a simple one dimensional spring mass system.

The question is, how do I determine the force experienced by the mass when it hits the ground? Then, I'll need to make an expression relating the maximum acceleration experienced by the object with all the other parameters.

Arif

#### BigKLaxer

• Jr. Member
• Posts: 20
##### Re: Spring mass question
« Reply #1 on: August 31, 2008, 09:06:39 AM »
I'm pretty sure the force enacted ON the mass is just m*g or mass*gravitational acceleration.  Then you can determine the velocity of the mass and find the kinetic energy.  Then you set the kinetic energy equal to the spring energy and find the compression of the spring.  Let me know if you need the formulas
Experimental Mobile Robotics Platform: http://www.udrobot.blogspot.com

#### arixrobotics

• Full Member
• Posts: 119
##### Re: Spring mass question
« Reply #2 on: September 01, 2008, 06:35:38 AM »

Actually, after posting on this forum, I forgot to check back and went on doing the question with what ever knowledge I have. And I submitted it already just now.

But I did somewhat similar to what BigKLaxer suggested.

Now I have another question; When an object is placed on the floor, it is experiencing a force F = mg by the floor, which cancels its weight, right? Then, if I let the object free fall from some height, when it hits the ground, it will still feel the same force F = mg, am I right?

How come the object feels the same force despite the different fall height? If that is true, how come eggs break when they fall 1 metre on to the ground, but not when it falls from 1cm off the ground?

Can anyone explain? I might be missing something here...

#### BigKLaxer

• Jr. Member
• Posts: 20
##### Re: Spring mass question
« Reply #3 on: September 01, 2008, 11:58:57 AM »
Yes you're right about the force being the same.  The reason the egg breaks at a higher height and not a lower is due to a change in momentum, not the force. The higher the Impulse (impulse=mass*velocity - initial mass*initial velocity) the harder the impact and the more likely the egg is to break.
Experimental Mobile Robotics Platform: http://www.udrobot.blogspot.com