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Old 05-10-2007, 01:41 PM   #71
tripleripple
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Default Re: Motorcycle Cornering Physics

I'm no engineer but I thought about this for awhile and came up with two ideas:



1) One day, when I have children (or when the ones I don't know about find me), I hope they aren't an inquisitive lot. I have no patience for questions like this.



2) I don't really care who/how/why. All I know is it works and it's a hell of a lot of fun. It's kinda like the light switch - I won't care why motorcycles lean in a turn until they stop doing so. Then I'll find out what the deal is.
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Old 05-10-2007, 01:54 PM   #72
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Default Re: Motorcycle Cornering Physics

Wilbur and Orville Wright did the pioneering and definitive work on two-wheeled steering. It's a bit complicated, but there are simple demonstrations you can do in your driveway that show much of what's going on.



First, gyroscopic forces have little to do with getting the bike leaned over. You can use a level and a plumb bob to show what countersteering does. Tape a level to the frame of a bicycle so that it's vertical when the bike is vertical. Hold the front wheel straight in line with the rear. A plumb bob held somewhere by the seat can show where the centerline is. Now, with the bike held vertical, turn the front wheel to the left. You will see that the plumb bob moves to the right. The center of gravity of the bike moves to the right, which will cause the bike to fall to the right. (There is some dynamics stuff going on also, but most of the force causing the bike to lean is plain old gravity).



Once the bike starts to turn it has to lean to balance the centrifugal forces trying to push it over opposite the direction of the turn and gravity trying to pull it down in the direction of lean. Take a weight and a string, spin in a slow horizontal circle. The weight swings out. The faster you swing, the more it swings out. Fooling around with length and speed you can see that the important factor is the rotating speed (time per revolution). The less time per revolution the more the weight swings out.



To counteract that force the bike must lean more. The radius of the curve is controlled by how much turn in the direction of the corner you give the front wheel. The lean angle is "automatic". That is, as long as you don't fall in or out the lean ange will be set by the physics involved. You concentrate on stability, not what angle you need to lean at.



It may be a bit much for an 8-year old, but most can "intuit" the basics from these simple demonstrations.
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Old 05-10-2007, 02:13 PM   #73
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Default Re: Motorcycle Cornering Physics

First buy a gyroscope, great toy!
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Old 05-10-2007, 03:21 PM   #74
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Default Re: Someone call Bill Watterson, make him make more..

You might try, "Pearls Before Swine" as a reasonable substitute. Not yet quite C & H, but showing promise nevertheless.
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Old 05-10-2007, 03:23 PM   #75
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Default Re: Home Beatings

Good point. That's why I'm divorced!
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Old 05-10-2007, 03:29 PM   #76
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Default Well, Son, you see:

"The peripheral tyre speed will be slightly less than the road speed around the turn but there is now a sideways speed to the tyre, i.e. is it is sliding sideways. This lateral movement produces a force at right angles to the wheel direction. The magnitude of this force depends on the amount of slip angle, increasing up to about 15° and then falling off rapidly."



I'm sure I have a pencil around here somewhere.
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Old 05-10-2007, 03:42 PM   #77
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Default Re: Motorcycle Cornering Physics

"I hope they aren't an inquisitive lot"



I guess you mean "I hope they aren't kids". If you're going to have kids, get ready for the continuous questions. Like someone above mentioned. A good Calvin and Hobbes type answer works every time. But it can backfire. I told my kids so much BS that they don't listen to a word I say any more.
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Old 05-10-2007, 04:11 PM   #78
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Default Re: Motorcycle Cornering Physics

I seem to notice that the very first thing that happens when I push on the bar is that the tire actually ****s to the direction that I push- just about what you'd expect when riding a bicycle. But then very quickly, the bike tends to "trip" over the front tire due to straight ahead momentum. This causes the bike to "fall" in the direction that you want to go. After that , the physics gets too complicated for me.
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Old 05-10-2007, 04:58 PM   #79
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Default Re: Motorcycle Cornering Physics

It's all about vectors. Use the old water in a bucket analogy. Fill a bucket with water 1/2 way full. Now have him (your son) or you spin the bucket horizontally. Ask him what happens. If you spin it fast enough the water sloshes out. Now attach a strong rope to the handle and start spinning is vertically. Once you get the complete revolution, then change the vector to diagonal (like a cowboy's lasso). If you have the bucket spinning fast enought nothing will spill out. Explain to him that because the wheels are spinning, in order for you not to "spill out" you must lean. That should be simplistic enough for an eight year old (without addressing the fact that the vector forces of the wheels are in different directions, gravity, center of mass, center of gravity, etc. Oh, and don't forget the co-efficient of friction and the counterforce vector...). Hope that helps!
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Old 05-10-2007, 06:19 PM   #80
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Default Re: Someone call Bill Watterson, make him make more..

"Cow and Boy". Give it a week, it WILL grow on you.
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