Falling slinky released from top, slow motion

Slinky spring hanged and released, repeated experiment photography merged into a high-speed video, 3ms/frame. The bottom ring does not move until the collapsing spring approaches it.

Some explanation:
Obviously, the center of mass is falling with acceleration g from the start. It's also pretty obvious that at t=0 the bottom's acceleration is zero, because the spring strain geometry is still the same and therefore the forces are, too. So what is balanced stays balanced, the only thing having acceleration at the first moment is the very top point.

It is is less obvious that it will not move for some while, but it can be understood from wave physics: you are producting an event at the top, it needs some time for a wave to travel to the bottom with this information.

It is, however, much more subtle why the bottom doesn't move until the very top end just arrives and smashes it downwards boom. Before diving into computations, it can be suggested that the lingtitudal wave velocity declines when moving down, both because the density of the spring is growing and because the springs are normally illinear in such way that the spring coefficient grows with strain. This could make the wave slower and slower, until eventually overrun by the top end. I will leave that as an excersize to compute that :)

Additional credits go to Dr. Eli Raz from Technion, Yoav Merhav, Amir Laks, Omer Peneth, Braude college in Karmiel and it's lab personnel and myself.

Category:

Howto & Style

Tags:

• slinky
• highspeed
• timelapse
• repeatedexperiment
• physics
• waves
• slowmotion
• spring
• oscillations

[bugpwr]

Each frame of the 30fps video involved hanging the spring again and again, stabilizing it's oscillations, setting the shooting system to a new delay, etc - a whole day of work. The curtains were accidentally moved in the process, which demonstrates the approach. But you do see the correct shade of the falling spring :)

[sonypower159]

Defines newtons law . So is his laws safe to say accurate?

[djteac]

I just love how the bottoms stays in its place until the top hits hit.

[CheezMonsterCrazy]

Plus, the top of the slinky looks as if it is hanging from something.

[concerta]

aw man :(

[KirbyzDreamland]

yeah... thats stop motion...

[sharpielicker]

So then it was stop motion.

[benjaminveal]

errr... if this is slow motion, why are the curtains in the background moving so much? looks more like stop motion to me.