How much energy to cause metal to produce sparks?

[IDK3465]

Hey, I was wondering if there was an accepted formula for a feat like this? Specifically in the feat I want to calc, scrapping a box cutter against a wall so hard that it starts to spark fire. Would really appreciate it if someone could help.

 

[IDK3465]

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[IDK3465]

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[IDK3465]

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[IDK3465]

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[IDK3465]

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[Furudo_Erika]

I read that sparks happen when metal reaches it's combustion point.

For steel, this is like 704°C to 760°C.

So I think it's a specific heat thing;
mass of material removed * specific heat capacity * temperature difference

(Assuming 20°C room temperature, that would be a difference of 684°C to 740°C)

 

[IDK3465]

I read that sparks happen when metal reaches it's combustion point.

For steel, this is like 704°C to 760°C.

So I think it's a specific heat thing;
mass of material removed * specific heat capacity * temperature difference

(Assuming 20°C room temperature, that would be a difference of 684°C to 740°C)

Thanks for the info, but then I wonder how much of the steel is being heated? Is it some percent of the total or is it just the mass of the sparks themselves? This feat comes from a book so I have no visual to work with here.

 

[Furudo_Erika]

Thanks for the info, but then I wonder how much of the steel is being heated? Is it some percent of the total or is it just the mass of the sparks themselves? This feat comes from a book so I have no visual to work with here.

Probably equal to the blade's thickness and width, times the length of the gash it made to get the volume of the metal that was shaved off.
I dunno, hard to say without an image. I also dunno if that box cutter uses utility blades or snap blades.

Can you get a line from the book at least?

Though odds are, it's gonna be a pretty low feat in terms of energy

 

[Furudo_Erika]

I looked up utility blades and found dimensions of one brand:
2.4” length
1.25” width
0.75” height
0.6mm thickness

What we want from this is height and thickness, which gets 0.00001143 m^2
Let's assume the distance is equal to the distance an arm moves in a 90 degree rotation, assuming a 0.75m arm; 1.178m moved.

0.00001143 x 1.178 = 0.00001346454 m^3 of material removed.
Density of steel varies, but let's use 8,050 kg/m^3 = 0.108389547 kg of material removed.

Specific heat capacity of steel is like 420 j/kg*C:
0.108389547 x 420 x 684 = ~31,138 joules (9-B)

Just my take on it, I ain't exactly a calc member, and this may even be the upper end of such a feat as this assumes the blade went its entire depth/height into the wall and uses the higher end of steel densities, and also assumes the blade made contact with the wall during the entire swing and not just "grazing" it.

Lower ends may only get into 9-C.

 

[IDK3465]

Here's where the feat comes from.
Maybe that would help you?

 

[Vzearr]

Here's where the feat comes from.
Maybe that would help you?

Creating sparks on a wall is like, human level.

 

[Furudo_Erika]

Creating sparks on a wall is like, human level.

Depends on exact material too, but that's not really important on such a small scale.

Neodymium magnets can cause sparks on collision, and abrading steel against flint causes steel to flake off and spark (which is...kinda how flint and steel even works), also there was that one Vsauce video where he caused sparks by smashing two metal balls together like the gigachad he is.

Either way, yeah. It doesn't take much energy at all to make sparks.

The upper end was assuming the blades left pretty deep gashes in the wall and caused all the material shaved off to spark from the friction. But if the blades were simple being dragged across without leaving much of an impression...it would probably even be as low as 10-C.

 

[IDK3465]

Depends on exact material too, but that's not really important on such a small scale.

Neodymium magnets can cause sparks on collision, and abrading steel against flint causes steel to flake off and spark (which is...kinda how flint and steel even works), also there was that one Vsauce video where he caused sparks by smashing two metal balls together like the gigachad he is.

Either way, yeah. It doesn't take much energy at all to make sparks.

The upper end was assuming the blades left pretty deep gashes in the wall and caused all the material shaved off to spark from the friction. But if the blades were simple being dragged across without leaving much of an impression...it would probably even be as low as 10-C.

Damn, well, it was a good try at least.

 

[IDK3465]

Wait hold on…

If we assume the part of the metal that has reached the point of combustion to be 1 cm length-wise, and we assume the blade to have an edge angle of 45 degrees, then the area of the heated metal is 0.5 cm^2. If we also assume a thickness of 0.6 mm, then the volume would be 0.03 cc.

Considering that the total amount of box cutters is 12, (1 + 1 + 2 + 3 + 5 = 12) then that means 0.36 cc or 3.6e-7 cubic meters.

Putting that into Furudo’s formula from before:
(3.6e-7 * 8,050) * 420 * 684 = 832.53744 joules (Street level)

Even at lower end steel densities, it would still be in the 9-C range. Please tell me if I’m wrong at all.

Also by the way, unlike the few sparks made by bashing two metal balls together in a single consented point, like what Vsauce did. What Trixie is doing here is a constant stream of sparks as she walks, making it more akin to like metal working or something, so not too keen on it being merely 10-C

 

[Flashlight237]

I don't think there is a specific energy value for this. Angle grinders, which I've personally seen at my workplace, can cut through steel. They use abrasive disks to achieve this task.

 

[Furudo_Erika]

Also by the way, unlike the few sparks made by bashing two metal balls together in a single consented point, like what Vsauce did. What Trixie is doing here is a constant stream of sparks as she walks, making it more akin to like metal working or something, so not too keen on it being merely 10-C

I mean...you can continuously flick a lighter and create a prolonged series of sparks.

The abrasion/friction is what causes the sparks. Now sparks can get pretty hot ("Ferro rods produce 3,000º F sparks while flint and steel sparks are in the 800º F range")., but sparks are very small particles of metal that has been heated up by friction.

 

[IDK3465]

I mean...you can continuously flick a lighter and create a prolonged series of sparks.

The abrasion/friction is what causes the sparks. Now sparks can get pretty hot ("Ferro rods produce 3,000º F sparks while flint and steel sparks are in the 800º F range")., but sparks are very small particles of metal that has been heated up by friction.

Dang…
Maybe I just can’t accept that any normal person can just make a rain of sparks just by scraping a wall. Idk, maybe it’s just hard for me to see but if what you say is really correct then I guess it’s really not anything substantial, just kinda disappointing…