Friction and Elastic Collisions

[brinton]

Primitive Experiments on Friction and Elasticity of Collisions Completed

I’ve been doing some additional work on friction in Incredibots. By experimentation I found that the angle of repose under normal gravity, that is the angle of an inclined plane at which an object begins to slide, is around 25 degrees. That means the coefficient of static friction is around .466. Further experimentation showed that the coefficient stayed the same at variable gravity, so friction responds under different gravities in IB as it normally would in real life, despite the fact that IB gravity isn’t quite the same as real gravity in every respect. Finding the kinetic coefficient of friction proves to be more difficult. I’m studying the physics involved and trying to design an experiment to calculate it, and after that to translate it into terms the IB community can use.

I’ve also been working on elasticity of collisions. Unfortunately I didn’t set my experiment up using standard units, so the exact numbers would mean little if anything. Here’s what I did. In zero gravity, I placed two balls propelled by blocks set behind them which were attached to fixated objects with sliding joints. The balls traveled toward each other, collided, and bounced backward in the direction they came. I measured the amount of frames it took for a ball to travel to a predetermined starting point, then from that point to the collision point, to measure the pre-collision speed and thus the momentum. I then measured the amount of frames that it took the ball to return from the collision point to the starting point, to determine the post-collision speed in relation to the pre-collision speed and thus determine the amount of kinetic energy that was lost in the collision. At an initial speed generated by thrusters set to 15, the collision caused a 71.15% loss in kinetic energy. At an initial speed generated by thrusters set to 5, the collision caused a 80.5% loss in kinetic energy. I don’t know if the thrusters acted on the objects long enough to get to full speed so attempting to extrapolate these results to other thruster speeds is impossible. Also, I’m not certain anyone has determined how different thruster settings relate to each other in terms of terminal speed. In any case, it appears that the greater the speed involved the more elastic the collision becomes. I’m not sure how that matches up to real life, but it does bode well for my and others’ experimentation with super-observable speeds, in that a collision moving at extreme speed would at this point appear to generate a very small loss in energy.

[RandomOutcome]

very interesting... but your point is...?
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[jayther]

Nice find and experimentation, brinton! Maybe if we actually set up a standard for length units (that some pople started a long time ago), you could actually put some numbers with units on the collisions.

[brinton]

I think giving the units in LPR/sec would probably be fine, though I still have the number for the fairly precise conversion of LPR to meters somewhere. Part of the reason I didn't take the time to set it out in exact units was that I was doing other things at the time and that the whole thing was done in a fairly confined area. I wanted it all small enough I didn't have to keep scrolling back and forth to set up the win conditions and also it was easier to keep the balls lined up exactly so that their post-collision path matched their pre-collision path.

Having the exact units doesn't matter as much as just finding the ratios though. How elastic are things, and how does speed of the collision (or is it total energy of the collision) change that elasticity? The next step will be to try different masses, and try to make sure that the thrusters have time to reach full speed.

[RandomOutcome]

[willempiee]

[brinton]

Upon further examination and eliminating some possible causes of inconsistencies it appears that my original hypothesis about elasticity was wrong. In testing collision with one object against a fixated wall, and allowing the thrusters to reach their maximum speed, testing at speeds 5 through 20 in increments of 5, the object loses from 81.9% to 83.3% of its energy, without the variable speed apparently causing the inconsistency. I know this is a small data set, but it takes a few minutes to check each speed since three data points have to be gathered at each one. Because sometimes the challenge system loses a frame before the winning condition being met is recognized, I believe that it’s the imprecision of the system causing the variation and that the true elasticity of collisions in IB equals around 82.5% loss or 27.5% maintained, however you want to figure it.

I don't know who invented the term LPR and SPR, though I was involved in converting that to meters with some precision. My original suggestion for standard units was somethign else, but LPR and SPR seemed to catch on and I've been using it ever since.

By the way the experiment above let the thruster run for about 1 LPR and then was tested over a 5 LPR distance. At thruster speed 20 the ball went 3.06 LPR /sec pre-collision and 1.39 LPR / sec post-collision. I do wonder if the shape of contact in the collision makes any difference, but maintaining a non circular orientation through the point of contact might be difficult. Due to the compression of the objects together as they collide, decreasing the area of the collision relative to the mass might make a difference in the elasticity. Too many variables, too little time. I'll try to get to this next week. I have a busy next couple days.

As far as changing the shape of the objects go, the original experiment used two balls colliding and the data was fairly consistent until I decided to start from scratch, and I got about the same numbers as here. I just had that one bad data point and i was the first one I did and that made the whole thing feel suspect.

[AssassinatorPie]

Under specific experiments, more dense objects will become subject to less of an angle than less dense objects, its not entirely about weight in this case.

I hate doing trial and errors, such waste of time for little progress to find the correct formula for things.
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[Darkfangs]

This is great. Adding.
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[b0tman]

Brinton, I'm sure glad you have the patience to do these tests! Though I've wondered a bit about such things, I've never been so curious as to spend any real time running the experiments to find the answers. However, I always look forward to reading about your latest research!
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[Darkfangs]

I am elated that you decided to do things for IB Physics, brinton.
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[Robot Kings Minions]

Does brinton have a 6-month supportership? If not, SOMEONE SPONSER HIM SO HE MAY CONTINUE HIS INCREDIBLE RESEARCH!
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[robots rock]

I would if I could.
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[Bongoro77]