MadSci Network: Physics

Re: What forces enable motorcycle to go through turns at the highest speeds?

Date: Sun Apr 16 14:35:23 2000
Posted By: Vernon Nemitz, , NONE, NONE
Area of science: Physics
ID: 955242334.Ph

Greetings, Nancy:

The main force involved is friction.  Without the friction associated with 
the rubber tires contacting the road, the motorcycle would go only in a 
straight line.  This is, of course, in accordance with Newton's First Law 
of Motion. And if you have ever encountered a patch of sand or gravel 
while making a sharp turn, I am sure you noticed what happens when that 
essential rubber/road friction becomes suddenly greatly reduced: The bike 
falls onto one side and slides in a fairly straight direction.  (Ouch.)

The reason you lean while performing a turn is entirely due to something 
that you may have neglected to remember.  I therefore invite you to get on 
your motorcycle, and to drive around a curve WITHOUT leaning -- but I 
don't recommend it!  For safety, let's consider an automobile for a 
moment:  If you are belted down into your seat, and the car goes quickly 
around a curve, you will note a tendency for your upper body to lean in 
the direction AWAY from the center of the curvature.  This is again the 
First Law of Motion in action; the inertia of your body IS the tendency to 
maintain a straight course, while the car is using its rubber/road 
friction to turn away from that course.  More regarding this can be found 
in another Answer, involving balloons in a car.

So...if you were on a motorcycle, going around a curve without trying to 
lean, inertia would tip you over and lead to a wipe-out.  (Ouch again).  
We don't worry about this in a car, because it has four wheels on the 
ground; they provide so much stability that the car leans very little, 
while the passengers can be caused to lean a lot.  When motorcycling 
around curves, the reason you deliberately lean toward the center of the 
curvature is to counterbalance that inertia-caused outward lean.  
Furthermore, the faster you go around a curve, the greater the 
inertia-caused lean would be, and so the more you must counter-lean (and 
the more you must hope that your rubber/road friction will suffice to keep 
you on your chosen curve).   That's all.

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