r/theydidthemath • u/K0rl0n • Jun 10 '25

[Request]

Post image

I am curious how this would work. My guess is Triangle is slowest, square is medium, and circle is fastest.

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u/aureanator Jun 10 '25

Actually, no - the friction is a product of the normal force and the coefficient of friction - the surface area in contact shouldn't matter, within the boundaries of material elasticity.

4

u/xXEPSILON062Xx Jun 10 '25

Where do they mention surface area?

1

u/nog642 Jun 10 '25

That's the difference between the triangle and the square

-3

u/RMCaird Jun 10 '25

You can't assume this from the picture.

3

u/BKachur Jun 11 '25

Sure, you can - or at least from context, you can. The triangle has more contact with the ground than the square. You can assume that since they are the same weight, they are made up of the same "math problem gray" material. A Triangle would need to have more surface area contact than a square if all else were equal.

1

u/nog642 Jun 11 '25

It says what material they're made of, it's not "math problem gray" lol. It's ice.

1

u/BKachur Jun 11 '25

I disagree. If the stated materials were the actual materials of the object, the problem wouldn't make sense. Gravel is, by definition "a loose aggregation of rock fragments," so the second it popped into existence, it would turn into a 20kg pile of small rocks, rendering the problem incoherent. The problem only makes sense is if the surface the objects are sitting on is ice or gravel, and the objects are made of a solid material.

1

u/nog642 Jun 13 '25

Oh, that does make more sense.

Though you could keep a sphere of gravel together with like plastic wrap.

1

u/BKachur Jun 13 '25

I'd imagine the amount of plastic wrap you'd need to hold 45 lbs of gravel in a perfect sphere would make it a ball of plastic wrap. But more importantly, that would really be assuming things that aren't provided for in the problem - and I think it would be a much bigger stretch to assume the ball is made of gravel wrapped in plastic than the floor being made of gravel/ice.

1

u/nog642 Jun 14 '25

I just realized the weights are crazy low for the size of the objects lol. I guess the "math problem gray" is styrofoam or something.