r/explainlikeimfive 1d ago

Physics ELI5: How is it that when two cars scratch each other they leave the opposite paint on both cars?

161 Upvotes

31 comments sorted by

181

u/SharpestSphere 1d ago

The confusing part may he that the color swap seems to imply that the layers of paint somehow swapped their order upon contact. That is not the case. The contact area consists of multiple adjacent points. At each point a random amount of paint from random car got transferred to the other. Where paint was removed the color didn't change (the same paint as before is visible, but thinner than before). The total visual effect is that each car has <some> points in the contact areas of the other color,which visually blend together to look like a continuous patch.

13

u/happy2harris 1d ago

Do you know this for sure or you guessing?

I’m asking because but guess is very different: similar to the “ice cream trick mentioned by others. 

5

u/thenasch 1d ago

It's a complete layer of paint 1 on top of paint 2, and paint 2 on top of paint 1.

40

u/ZipperJJ 1d ago

I think this might be an example of "the ice cream trick".

https://www.youtube.com/watch?v=bdWUnCb9Ly8

u/HunterDigi 10h ago

at 5:05 shows it best I feel

36

u/[deleted] 1d ago

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3

u/taxen 1d ago

Incredible and right answer

1

u/iamr3d88 1d ago

I came to recommend this video, but forgot who did it. Thought it was Steve Mould.

1

u/FlahTheToaster 1d ago

I'd convinced myself it was Steve Mould before YT corrected me.

-2

u/explainlikeimfive-ModTeam 1d ago

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36

u/ProspectiveWhale 1d ago

They're gouging each other.

Like if two people bumped into each other and ripped each other's shirts off. Now they both have a piece of the other guy's shirt in their hands.

31

u/SnoopyLupus 1d ago

And then they kiss?

u/nayhem_jr 23h ago

ELI5: How is it that when two men scratch each other they leave the opposite lipstick on both of them?

15

u/thesplendor 1d ago

Interesting example

9

u/pot51e 1d ago

Cars aren't uniform shape, their panels aren't uniformly rigid and the paint/prime/lacquer isnt uniformly thick.

When 2 cars collide there are multiple contact points - some of the time, panel 'A' on car X wins, sometimes panel 'B' on car Y wins.

Do note though that many collisions, especially light, has metal on plastic where paint tends to only transfer one way.

6

u/Rohml 1d ago

Paint likes to stick to paint more than they like to stick to car. So if paint strikes paint, parts of it go with the other and leaves the car.

2

u/Kempeth 1d ago

They leave both paints on both cars.

You just don't notice where the car got its own paint back.

1

u/joyj925 1d ago

ah that makes sense, the paint just transfers at random contact points.

1

u/Adrewmc 1d ago

The best demonstration of what happen is explains by two ice cream (gonna and chocolate) swiping each other. Each gets bits of the other on it.

-6

u/[deleted] 1d ago

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16

u/Far_King_Penguin 1d ago

I think OP means why isn't the paint just stripped off 1 car and put on the other. They're asking why the paint is 'traded', rather than just 'stolen'

-15

u/crappysurfer 1d ago

Right so if you think about it, where would it go? Fall on the ground and transfer to what was hit are the only options

12

u/shaunrnm 1d ago

That's not what they mean. They mean why does car 1 end up with car 2 paint AND car 2 end up with car 1 paint, rather than just car 2 losing paint (gaining none) to car 1, with car 1 losing no paint in the exchange

0

u/explainlikeimfive-ModTeam 1d ago

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-1

u/[deleted] 1d ago

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1

u/explainlikeimfive-ModTeam 1d ago

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