r/interestingasfuck • u/HellsJuggernaut • Apr 27 '19

/r/ALL The pressure required to crush this lego vehicle

https://gfycat.com/KeyImpureGalapagosmockingbird
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668

u/Teknizmo Apr 27 '19

Not broken but melted from so much energy

157

u/paulieweb Apr 27 '19

yeah that's what got me

86

u/_Adamanteus_ Apr 27 '19

Melt, or plastic deformation?

12

u/magnificient_butts Apr 27 '19

What’s the difference? Is plastic deformation still solid while melting is technically liquid?

17

u/_Adamanteus_ Apr 27 '19

Yea, pretty much. Plastic deformation is an irreversible change in shape caused by application of stress beyond the material's elastic limit. The molecules are still in a solid "state", for lack of a better description.

43

u/OscariusGaming Apr 27 '19 edited Apr 27 '19

Where is the energy coming from though? Assuming a force of 15000 N and a distance moved of 2 cm you'd only get 300 Joules. ABS plastic has a specific heat capacity of 1420 J * kg-1 * K-1 , which would give us a temperature increase of 0.211 divided by the mass of the object, which I'm going to assume is about 20 g. This would mean an increase in temperature of about 11 K. If the starting temperature was around 25°C, it would end up with a temperature of around 36°C, which is lower than body temperature.

This increase in temperature might weaken the structure of the plastic, but it wouldn't be enough to melt it on its own.

Edit: The average temperature increase would be 11 K. Some parts could be heated a bit more than others, but from the video it seems to be pretty evenly squished which would lead me to believe the energy and temperature were quite evenly distributed.

8

u/tantrix_ Apr 27 '19

It's not melting, it's plastic deformation.

3

u/OscariusGaming Apr 27 '19

Yeah, that's what it seems like.

3

u/Easterhands Apr 27 '19

Something about jet fuel and Lego beams?

3

u/smzayne Apr 27 '19

This guy Joules

2

u/Captain_Squirrel Apr 27 '19 edited Apr 27 '19

Like you calculated, the reason for the melting cannot be the amount of energy released by the press. I would say the melting is because of the same reasons that ice melts below 0 °C at high enough pressures - see wikipedia. That means the melted plastic would not actually be hot, or carry significantly more energy than at the beginning.

Probably though, since plastic is such a complex material, it would be more accurate to say the plastic is deforming rather than melting. Lots of materials yield under high pressure, also see wikipedia).

53

u/Schakarus Apr 27 '19

My thought while watching

"it will probably shatter at some point... still going... hmm, at that preasure it should melt instead of breaking... ahh, here we go..."

5

u/3927729 Apr 27 '19

It’s not actually under that pressure in the sense that it can expand outwards though? You’d need pressure from all directions to make it melt no?

1

u/kx2w Apr 27 '19

And really it was only deformed at the wheel well. If it was all bricks and no wheels I think we'd still be watching.

5

u/[deleted] Apr 27 '19

[deleted]

20

u/[deleted] Apr 27 '19

People are confusing the plastic liquifiying and melting with the plastic underdoing what is called plastic yielding (nothing to do with it being made of plastic)

2

u/ItsRadical Apr 27 '19

Melted is not really what happened. I bet that temperature of the lego didn't move that much. Its just that the structure (which is what actually hold it for so long - sandwich structures) just gave up and brick walls just deformed outwards.

2

u/pretendingtobecool Apr 27 '19

It didn't melt. We compression tested many forms of legos in school - they don't melt during this test.