Falling ladders - why does this happen?

What happens when a chain ladder lands on a table? Great video and concept by Andy Ruina. Let me know if you want me to post a follow up explaining the answer.

[cicalinarrot]

Plot twist: he has no idea why that happened and he's genuinely asking, hoping that someone tells him in the comment.

[heftylad]

For those wondering, you see how the rods are alternating diagonal? When the downward part of the bottom rod hits the table, it bounces up, pulling the other side of the rod, and therefore that rope, downwards. Rinse and repeat with every rod, all pulling slightly downwards on the ladder, and now it's falling faster than the other.

[mikecurtis]

Since the rungs are angled, the table is causing them to flatten out, which pulls down on the rung above it. This alternates left to right, gradually speeding it up.

Edit: Never expected my comment to get so much attention. To elaborate a bit, one needs to understand that even the ladder on the right will speed up after it hits the ground, just like the one on the left. The only reason you see the difference is because the one on the left hit the table (higher ground) before the one on the right. Also, to better see the pulling effect, don't just watch the strings close to the table. Look closer to the top of the ladder, like two or three rungs from the top after the top comes into view. You can clearly see motion in the strings that is not seen in the ladder on the right.

[bryh]

When the lower part of the slanted rungs hit the table, it causes the lower side to bounce back up from the hit, which pulls the other side of the rung, the upper part with the shorter string, down faster, which is adding downward pull alternating side to side with the ladder on the left.

[Bozza]

Since everyone has a long and over-complicated answer:

- Ladder steps are angled.
- One side of the ladder step hits the floor first.
- Creates a torque (rotating force).
- Torque creates tension in the shorter string.
- The ladder falls slightly faster.

[IdoAloni]

The key thing is that the steps are angled in an altering pattern.
As a step hits the table, a rotating force is applied on the step and pulls the next step, and applies a rotating force in the other direction.
The interaction pulls all of the steps down every time a step hits a table.

That's why the left latter falls quicker.

[kaelenanderson]

This happens because each rung on the ladder is tilted. As each rung hits the table it pulls the string it's attached to downward a bit, causing the ladder to fall faster.

[zaydenmanton]

You explained that problem beautifully!!👍👍👍

[psyskeptic]

When the angled rings hit the table they exert a tiny accelerating force on one string, via angular momentum. When the next ring hits, it tugs a tiny bit on the other side string. So you get a series of tiny angular momentum tugs on the strings, adding to the g acceleration.

[willnash]

Basically, as each tilted steel rod falls, it bounces up a little on impact. This causes them to gain some torque that properls the other end downward faster. The taut string on that side allows that increase in speed to pull the ladder down slightly faster, while the non-taut longer string on the other end prevents the bounce from pushing the ladder up to slow it down.

[mitchellminer]

The angled sticks are the key. The center of mass of each stick is in the middle. When the lower end of the stick hits, the center of mass keeps falling at the previous speed. That makes the stick rotate around the contact point, and the far end of the stick increases speed. The upper end of the stick moves down faster than it did previously, and it pulls on the rest of the ladder.

[VanshAsvani-ulpk]

Because of the arrangement of steps in the ladder as second one is free falling the arrangement doesn't effect the rate of flow but in the first case due to arrangement of steps touches the step coming above it and saves some time as the step above it needs to travel less and hence takes less time another reason is that the first one is piling up and the step above it has to cover less distance as compared to the second one

[tylerdurden]

It's because the ladder has angled steps (planks).

When the planks hit the ground, only the tip of the plank makes contact with the table, causing the plank want to rotate around it's centre of mass (converting the planks normal momentum into angular momentum).

This causes the other end of the plank to also rotate around the centre of mass. But there's a string connecter to the plank above that, so it pulls down on the rope(gives a tugg and tension in the rope increases, all the way up to the top).

The next plank is angled the other way, so it's the other side that hits the table first.

So each time a plank falls, a downward tugg is given at the opposite end, alternating left and right.

These tuggs add additional acceleration to the planks that are still falling, in the same downward direction.

[dayashankarsuresh]

The angled sticks ensure that tension transfer is not uniform at both edges in the next stick. This, in a way, generates torque, and this torque guarantees that the upcoming stick is pulled down faster. The pulling force accumulates and is most noticeable at the last stick.

[selmanbilgen]

On the left, when an end of a step ( the one closer to the table surface) hits the table, a rotational force is created on the opposite side of that step, and that force pulls the shorter string down.

[gcurious]

A key to this trick is the alternating slanted bars. One end of a bar hitting the table causes the other end to pull the short string due to the rotation around the center of gravity of the bar. The short string is pulled and in turn the next bar is pulled slightly. As a result, the ladder experiences more pull (downward force) compared with the other ladder.

[allenkostner]

Because the rungs are at an angle. Once they hit the table there’s a rebound effect that causes more tension on one side than the other. The tension yields a secondary “pulling” force that acts in conjunction with gravity, therefore speeding up the time it takes to hit the table which is higher than the other ladder.

[Annorach]

->Shows us a cool video
->Asks us why it happened
->Leaves without an answer

[cconnon]

The diagonal rods hitting the table push up on the rod, but the center of mass of that rod is in the middle so it’s pulling down on the opposite side just a little bit. This could be just a 10th of a percent but you had all the wrong together and it’ll fall just a few percent faster.

[enniomorabito]

The thing to point out is that the ladder rungs are angled. Once the angled ladder rungs hit the table there is a pulling action that takes place when one side of the rung hits, and the other side is pulled down because of the impact. This causes the rope of the latter on the left side to be pulled down faster.