Where is this energy coming from?

[Raider5678]

So I was watching a video on bottle busting. Basically, you take a non-carbonated liquid, smack your hand onto the top of the glass bottle, and then the bottom of the bottle shatters.

This happens because the bottle moves down faster than the water, creating a vacuum at the bottom of the bottle.

The water then rushes to fill that gap 10x faster then what you hit the bottle with. Effectively, it seemingly magnifies the energy to break the bottle. 

But that's impossible, and I know it. 

 

So where did the extra energy come from? Assuming you transfer 7 kilograms of force to the top of the bottle, why does the bottle break from a force of 70 kilograms(estimate)?

Where did that extra 63 kilograms of energy come from?

 

Now that I'm thinking about it I'm realizing that just because it's faster doesn't mean that it's got more force, but just to confirm I'm still asking.

 

 

The video I saw this on:

He was a NASA engineer once and he explains it.

 

[Endy0816]

This source talks about it being caused by cavitation:

http://www.livescience.com/24469-bottle-exploding-secret-revealed.html

Cavitation is interesting. Small volumes result in some novel oddities like this.

Edited October 27, 2017 by Endy0816

[studiot]

2 hours ago, Raider5678 said:

So where did the extra energy come from? Assuming you transfer 7 kilograms of force to the top of the bottle, why does the bottle break from a force of 70 kilograms(estimate)?

Where did that extra 63 kilograms of energy come from?

I didn't watch, but I assume he didn't actually say 63 kilograms of energy? 

Or was that why he is a former NASA engineer? 

 

Glass tends to have very high residual stresses compared to its strength, which is why it shatters so readily and suddenly, sometimes without apparent cause.

 

https://www.google.co.uk/search?q=residual+stresses+in+glass&ie=utf-8&oe=utf-8&client=firefox-b&gfe_rd=cr&dcr=0&ei=I1nzWb2bJJyr4gSTipmYAw

[J.C.MacSwell]

Many times I have done a very similar trick with beer or wine bottles full of water, where I push a finger in it to hold a bit of pressure with a good seal then pull the finger out creating a negative pressure up until the seal is suddenly broken. Just like with cavitation the damage is done on the collapse, not creation, of any bubble. The bulk modulus of water is quite high and creates a shock to the brittle glass from the high peak forces. That bottles tend to break around the perimeter of the base but never perrfectly

[Raider5678]

6 minutes ago, J.C.MacSwell said:

Many times I have done a very similar trick with beer or wine bottles full of water, where I push a finger in it to hold a bit of pressure with a good seal then pull the finger out creating a negative pressure up until the seal is suddenly broken. Just like with cavitation the damage is done on the collapse, not creation, of any bubble. The bulk modulus of water is quite high and creates a shock to the brittle glass from the high peak forces. That bottles tend to break around the perimeter of the base but never perrfectly

Yeah. I was thinking if there was a way to set up like 10 "bottle contraptions" that use this same principle to make the water go faster and faster with each hit.

[swansont]

6 hours ago, Raider5678 said:

So I was watching a video on bottle busting. Basically, you take a non-carbonated liquid, smack your hand onto the top of the glass bottle, and then the bottom of the bottle shatters.

This happens because the bottle moves down faster than the water, creating a vacuum at the bottom of the bottle.

The water then rushes to fill that gap 10x faster then what you hit the bottle with. Effectively, it seemingly magnifies the energy to break the bottle. 

But that's impossible, and I know it. 

 

So where did the extra energy come from? Assuming you transfer 7 kilograms of force to the top of the bottle, why does the bottle break from a force of 70 kilograms(estimate)?

Where did that extra 63 kilograms of energy come from?

kg is a unit of mass. Not force, not energy.

6 hours ago, Raider5678 said:

Now that I'm thinking about it I'm realizing that just because it's faster doesn't mean that it's got more force, but just to confirm I'm still asking.

It could have more force, since that's not conserved. The whole point of some mechanical devices is to exert a force greater that the input. The hammer in the video. Pulley systems. A lever.

it could be as simple as the joint at the bottom being the weak point. It's not in line with the shock.

[J.C.MacSwell]

9 minutes ago, swansont said:

kg is a unit of mass. Not force, not energy.

It could have more force, since that's not conserved. The whole point of some mechanical devices is to exert a force greater that the input. The hammer in the video. Pulley systems. A lever.

it could be as simple as the joint at the bottom being the weak point. It's not in line with the shock.

Maybe not the shock per se, but both maximum shear loads and bending moment get transferred there from across the bottom. Maximum tensile stress can occur on the inside at around that point (perimeter) depending on shape and thickness.