Here is a thought experiment, followed by a demonstration

Hold a slinky vertically, off of the ground, so its stretches itself out.

Let it go, holding from the top. It will begin, of course to fall..

The question is.. When will the bottom of the slinky begin to fall? Why?

http://www.youtube.com/watch?v=uiyMuHuCFo4

>When will the bottom of the slinky begin to fall?

When it notices that nothing’s holding it up.

>Why?

Same reason Wile E. Coyote doesn’t fall until he notices he’s run way off the cliff.

In real life I presume it’s waiting for the falling centre of mass to overcome the wire tension or suchlike.

Dropbear said:

Here is a thought experiment, followed by a demonstration

Hold a slinky vertically, off of the ground, so its stretches itself out.

Let it go, holding from the top. It will begin, of course to fall..

The question is.. When will the bottom of the slinky begin to fall? Why?

http://www.youtube.com/watch?v=uiyMuHuCFo4

When the stress wave initiated by you releasing the top reaches the bottom.

Because before then the resultant force on the bottom of the slinky will be zero.

yes it’s quite interesting that the bottom of the slinky doesn’t know it’s allowed to start falling until the stress wave as reached it …

i guess the speed of sound in a slinky is remarkabley slow

Dropbear said:

yes it’s quite interesting that the bottom of the slinky doesn’t know it’s allowed to start falling until the stress wave as reached it …

i guess the speed of sound in a slinky is remarkabley slow

Nice video.

It’s interesting towards the end they look at the end starting to rotate before the main compression wave gets there. There would be stresses travelling at the speed of sound in steel, running round the helix, that travel faster than the compression wave, even though that travels in a straight line.

The Rev Dodgson said:

Dropbear said:

yes it’s quite interesting that the bottom of the slinky doesn’t know it’s allowed to start falling until the stress wave as reached it …

i guess the speed of sound in a slinky is remarkabley slow

Nice video.

It’s interesting towards the end they look at the end starting to rotate before the main compression wave gets there. There would be stresses travelling at the speed of sound in steel, running round the helix, that travel faster than the compression wave, even though that travels in a straight line.

my video yesterday on the quantum foam was also interesting ;)

Dropbear said:

The Rev Dodgson said:

Dropbear said:

yes it’s quite interesting that the bottom of the slinky doesn’t know it’s allowed to start falling until the stress wave as reached it …

i guess the speed of sound in a slinky is remarkabley slow

Nice video.

It’s interesting towards the end they look at the end starting to rotate before the main compression wave gets there. There would be stresses travelling at the speed of sound in steel, running round the helix, that travel faster than the compression wave, even though that travels in a straight line.

my video yesterday on the quantum foam was also interesting ;)

This one?

http://www.youtube.com/watch?v=J3xLuZNKhlY

Yes.

Comment in empty space thread coming up.

There is a follow up video by the same author about quarks and higgs.

Dropbear said:

There is a follow up video by the same author about quarks and higgs.

This one?

http://www.youtube.com/watch?v=649iUqrOKuE

Very interesting too :)

nope
this one ..

http://www.youtube.com/watch?v=Ztc6QPNUqls

What I like most about the Slinky is that it’s the only walking robot with only one moving part.

mollwollfumble said:

What I like most about the Slinky is that it’s the only walking robot with only one moving part.

yes but if you want more than walking?

> yes but if you want more than walking?

Then make it from memory metal, or similar.