Cool Video of the Day

H

HardOCP News

[H] News
Joined
Dec 31, 1969
Messages
0
How do people discover stuff like this? Are you just sitting the house one day with a camera capable of recording at 300 frames per second and then start dropping stuff?
 
Also they say the tennis ball doesn't fall until the slinky completely contracts, this is incorrect as you can clearly see small movements downwards in the ball before it completes the contraction. This is a clear distinction from the first example.

Interesting bit, but clearly limited scientific value.
 
Ok, wtf happened to the tennis ball? This was no time for a season ending episode cliff-hanger, dammit.
 
Also I'm sure when we were all dumb and young, we had a shitload of fun with a slinky.
 
I predict that faster than light travel will be made possible with Slinkies and corn starch.
 
Very cool videos, I cringed a bit when he talked about information traveling down the slinky that said tension changed though... "information" will travel at the speed of sound through the object, so if it's a slinky, or a tennis racket or whatever... and that speed is MUCH faster than how long it takes the slinky to fall, at a bit over 340 meters per second, the information that the tension is changed went in a little more than 1 frame of footage.

What's really happening is the center if mass of the object is falling as if it was a single small object. Tension is pulling up, but tension is also pulling the top towards the bottom (Newton's law... opposite and EQUAL forces.. gravity is not tension), the bottom moves towards the top as well, just at the same rate that the whole thing is falling (probably, I'm too lazy to work the numbers).
 
BloodyIron said:
Also they say the tennis ball doesn't fall until the slinky completely contracts, this is incorrect as you can clearly see small movements downwards in the ball before it completes the contraction. This is a clear distinction from the first example.

Interesting bit, but clearly limited scientific value.
Click to expand...

Yeah, but you can see in the original video (not the slowmo) that when he let go, there was a small variation of downward movement with the ball still settling that is likely the reason that in the slowmo it seemed to move a bit downward. In reality the physics at play are true. The slinky is trying to compress both ends at the same time and since gravity is acting on one end, the upward force that normally would have moved the lower part of the slinky up is being mostly cancelled out by gravity. I am sure there is still movement but largely not perceived. Choosing a stronger spring would not show the same effect. The slinky is just a good example due to accessibility and near similar force required.
 
I don't see what is difficult to understand about this. It makes perfect sense to anyone that just thinks about it for a second. I don't like his use of "information". There is no data being communicated within the slinky. It is simply tension being released. Once the tension is released then nothing is left to counteract gravity and the slinky falls. All adding the ball did was increase the amount of tension required to hold it in place.
 
I don’t like the idea that the Slinky “knows” what time is right to start falling.
It evokes images of Wil-e Coyote standing in mid air not quite realizing how screwed he is.

Cool video though. Can anyone post the tennis ball outcome without me having to watch another vid?
 
sfsuphysics said:
Very cool videos, I cringed a bit when he talked about information traveling down the slinky that said tension changed though... "information" will travel at the speed of sound through the object, so if it's a slinky, or a tennis racket or whatever... and that speed is MUCH faster than how long it takes the slinky to fall, at a bit over 340 meters per second, the information that the tension is changed went in a little more than 1 frame of footage.

What's really happening is the center if mass of the object is falling as if it was a single small object. Tension is pulling up, but tension is also pulling the top towards the bottom (Newton's law... opposite and EQUAL forces.. gravity is not tension), the bottom moves towards the top as well, just at the same rate that the whole thing is falling (probably, I'm too lazy to work the numbers).
Click to expand...

Yeah, I'd like to see him give this same bogus explanation of "information" using the spring from a car strut. You know what that would look like with a tennis ball tied to it...it would look like you dropped a big spring with a tennis ball tied to it. This vid is all about a slinky being just the right kind of spring to contract at the same rate it falls and nothing else.

Pretty pathetic that they say "look it held up the tennis ball!" when anyone who isn't blind as a bat can see the tennis ball fell half way to the ground while the slinky was contracting.
 
sfsuphysics said:
What's really happening is the center if mass of the object is falling as if it was a single small object.
Click to expand...

As with any falling object, spring or no. He first the spring fall until, for the bottom of the spring, the spring force (tension) cancels gravity. Thus, when he drops it, the bottom does not fall until the spring collapses, that is, until the tension force is no longer present to oppose gravity, and then the spring falls normally as a compressed object. Note that, because you're letting the forces cancel before dropping, a stronger spring would have no effect here - it would simply not stretch as far and collapse sooner, but a higher spring force/length would not "hold up" the tennis ball better.

I believe the reason you're seeing the tennis ball fall a bit, where the spring by itself did not, is that the tension in the spring depends on its stretch. While he's holding the spring + ball, both forces cancel perfectly, but as it falls, the tension starts decreasing as it collapses, and thus over time gravity > tension, until the spring fully collapses and all you have is gravity. The effect is more obvious with the added weight of the tennis ball. Perhaps a more non-linear spring would help here (that is, one that holds lots of tension with little stretch, but adds less tension per unit length as you stretch further), but I don't know if such a spring exists.

I would like to see the demo added to by putting a red dot on the spring's center of mass, then dropping it at the same time & height as a small, solid object. If done correctly, the red dot and the small object should fall at the same rate and hit the ground at the same time.

Also, not the first time I've heard "information" in context with physics, especially quantum physics. It sounds odd and it doesn't add to the explanation, where more discussion of tension + gravity would.
 
For the tennis ball video (the 2nd one), why didn't they have the old guy climb up a ladder, and then drop the slinky and tennis ball?
 
Waste of a good SNES when people do crap like that, and most NES and SNES are easy to repair.

.And this is a SNES case that has mostly escaped the bad batches of plastic that caused them to yellow with age heat and UV light.

This dude should burn in hell for his sins.
 
Cube said:
Waste of a good SNES when people do crap like that, and most NES and SNES are easy to repair.

.And this is a SNES case that has mostly escaped the bad batches of plastic that caused them to yellow with age heat and UV light.

This dude should burn in hell for his sins.
Click to expand...

Wrong thread hmm :)
 
You must log in or register to reply here.
Back
Top