# A Visual Riddle (The Epitaph of Stevinus)

A physics riddle following the “Epitaph of Stevinus”.
A string of beads is placed on top of a triangular prism. One side of the string is longer, but the other is steeper, which raises the question: to which side the string will slide to, if at all?

This question was asked and answered by Simon Stevin over 400 years ago, in a thought experiment that proves
the mechanical advantage of inclined planes. I.e., it demonstrates that inclined planes can be employed amplify the force exerted by small weights, allowing them to lift heavier objects.

source

Fahad Hashmi is one of the known Software Engineer and blogger likes to blog about design resources. He is passionate about collecting the awe-inspiring design tools, to help designers.He blogs only for Designers & Photographers.

### 44 thoughts on “A Visual Riddle (The Epitaph of Stevinus)”

• September 29, 2017 at 3:05 am

I say the string assumes human form and begins to sing never gonna give you up

• September 29, 2017 at 3:05 am

over 100 dislikes? do people just hate to think, that much?

• September 29, 2017 at 3:05 am

Who said friction exists here?

• September 29, 2017 at 3:05 am

The perpetual motion string doesn't prove anything though because the friction of the string against the triangles' edge makes it so the string stands still. If it was true that the thought experiment in question proved that the triangle stood still, it would also prove that a triangle with a 1-foot side and 2 million foot hypotenuse would stay still, which is obviously incorrect.

• September 29, 2017 at 3:05 am

my calculations shows me that steeper side have more force… 😀

• September 29, 2017 at 3:05 am

It is not a proof of anything to appeal to the nonexistence of perpetual motion. I could say that "Well since perpetual motion machines do not exist I've banged your mom".

• September 29, 2017 at 3:05 am

Practically, the beads are strung, and can only rotate on an axis pointing in the same direction as the motion considered. i.e they will not rotate when travelling either left or right in the illustration. Thus, they will most likely drape where any point is at the junction of two beads, barring an extremely imbalanced force which can lift a bead over the point against gravity and friction.

• September 29, 2017 at 3:05 am

The right answer is, "either A or B." C is an unstable equilibrium.

• September 29, 2017 at 3:05 am

doesn't friction play huge role in what happens

• September 29, 2017 at 3:05 am

i'm pretty sure every perpetual motion machine has something BOUND to mess it up.

• September 29, 2017 at 3:05 am

Simon Stevin's Machine.

• September 29, 2017 at 3:05 am

Common sense isn't common.

• September 29, 2017 at 3:05 am

Lets say the one with more beads has weights in the beads. Would that make it possible to be a "PMM"?

• September 29, 2017 at 3:05 am

I say it will cause another gold rush

• September 29, 2017 at 3:05 am

You also have to prove a perpetual motion machine impossible. It is impossible, but it is not trivial nor common sense to show this. Of course, the meta-argument would be that since you are showing this to me and the world still has any sort of energy problems, it is a pretty darn safe assumption that it is not that easy to make a perpetual motion machine out of this trivial device.

• September 29, 2017 at 3:05 am

The acceleration due to gravity of an object on a slope, neglecting friction, is gsin(theta) or go/h. Multiplying that by the amount of weight on the adjacent side, we get acceleration=goa/h. Looking at th other side, theta'=90-theta, so sin(theta')=cos(theta). so the acceleration due to gravity is ga/h. Multiplying by the amount of weight on the opposite side, we get acceleration=goa/h again. So the acceleration due to gravity is the same on both sides and therefore the force is the same, it balances out since this device is essentially a pully. Sorry this is worded confusing, but it makes sense to me and my final answer is that it will not move. I will now look up and see if I am right.

• September 29, 2017 at 3:05 am

2 and a half minute unskippable ad….

• September 29, 2017 at 3:05 am

my reasoning to why it stays wich I chose is the right side is steeper and has less beads the left side less steep more beads. on the eye it looked to cancel eachother out and I was happy i was right not sure if the reasoning is good enough XD

• September 29, 2017 at 3:05 am

This arguments somehow only works when you already know the solution. That is that the forces at each end are equals. What happens if the prism is inclined?

• September 29, 2017 at 3:05 am

I didn't have time to watch the whole thing, because halfway through I got really excited about building my own perpetual motion machine. Thanks for the how-to guide!

• September 29, 2017 at 3:05 am

從永動機的角度來證明布滿在三角峰上的串珠只會靜止不動，而不會從任何一側滑動，否則會出現永動機。

• September 29, 2017 at 3:05 am

The beads would probably fall towards you because from the extra welding some debris was left on the beads so there's more weight on the side of the beads closest to you so they fall towards you

• September 29, 2017 at 3:05 am

"Stand still" is my answer… since the amount of beads compensates the angle of the side. Now let's watch the video and piss myself.

I was right, but the explanation was more ridiculous and stupid than the riddle itself XD a perpetual motion machine wtf.

• September 29, 2017 at 3:05 am

it's not perpetual, there's other forces like FRICTION. Plus adding the additional string is introducing more forces to the equation, thus altering the outcome

• September 29, 2017 at 3:05 am

you ignore basic physic laws

• September 29, 2017 at 3:05 am

you would need a magnet to pull the heavier part of the beads back up into position to start the propelling motion again. otherwise the heavy part of the beads will just hang at the bottom…so simple, add magnets to propell the beads over and over

• September 29, 2017 at 3:05 am

It would fall as friction would stop it

• September 29, 2017 at 3:05 am

at 1:32 you said that it's a perpetual motion machine but gravitational energy is constantly acting on it which makes it a non-perpetual machine…sir so can u please explain it

• September 29, 2017 at 3:05 am

how is this common sense

• September 29, 2017 at 3:05 am

how long are site AB and C

• September 29, 2017 at 3:05 am

how did I get here from a teacher-student rap battle?

• September 29, 2017 at 3:05 am

Who does the voices for these videos? You said before you do this by yourself.

• September 29, 2017 at 3:05 am

I do not believe that perpetual motion machines can exist, because it violates so many laws, however 1:43 does not violate any laws, and the statement of "without any energy source" is most likely invalid. Here's why:
gravitational potential energy.
The mass (and thus the weight) will be pulled down by gravitational potential energy, which will be converted into kinetic energy. Assuming that conditions were perfect (total vacuum meaning no air resistance or no heat transferred to surrounding area), the gpe would be converted to ke, and the velocity of the beads would increase in a counter-clockwise motion. The energy in the cycle would increase due to the added gpe from each turn, and it would, in a way, perpetually spin, while increasing the energy in the cycle.
The fault is that 1. heat will be radiated due to friction and 2. the gravitational potential energy would run out, given enough time (likely infinite), and because energy is equivalent to mass (e=mc^2), the mass would 'disappear' in a way, and would then be in the form of energy (infrared radiation given off and kinetic energy in the beads).
That is just another reason why perpetual motion machines can not exist.
No matter what, whether it be from mass into energy, or just energy itself, there would always be a source of the movement.
That is until you get into the quantum physics area, in which case everything just get ridiculously more complicated.

• September 29, 2017 at 3:05 am

adding weight to the beads doesn't make it a perpetual motion device though. Now youve changed the force being enacted on the beads. that was lazy.

• September 29, 2017 at 3:05 am

Tell me if I'm wrong —–>

Let the longer side of string be L, and the shorter one be l.
Mass of longer side — (ML/L+l) ; Mass of shorter side — (Ml/L+l).
Let A be the angle opposite to the shorter side (Shorter Angle), and B be the angle opposite to the longer side (Bigger Angle).

Taking the string as one system >
Forces on the System :
(ML/L+l).g.sinA parallel to the side L
(Ml/L+l).g.sinB parallel to the side l.

If we consider these two forces to be equal >

(ML/L+l).g.sinA = (Ml/L+l).g.sinB
Thus, L.sinA = l.sinB

This has to be true (or the sine rule would be wrong).

• September 29, 2017 at 3:05 am

So by extension, the static block could be any shape, no? So long as the whole chain of beads rests in it and the left and right ends are at the same height, the same argument can be applied to state that the ball chain remains static… right?

• September 29, 2017 at 3:05 am

I knew it from the start

• September 29, 2017 at 3:05 am

Bro the video isn't cool … Because after you attach the lower string to the upper the force on the lower is greater than the differences between the upper two and hence it automatically gets balanced as the upper one is not allowed to move.
It's like a thin person and an average person are fighting and then a 6 pack guy enters the show… How would either of the thin or the average guy win against this one…

• September 29, 2017 at 3:05 am

What if there is less friction on one side?