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Name: Ralph B.
Status: educator
Age: 40s
Location: N/A
Country: N/A
Date: 5/24/2004


Question:
I teach a motorcycle course and I understand about countersteering and the physics that go into it. My question focuses on the idea of the Coriolis effect and how it effects motorcycle turning. In the northern hemisphere we notice that riders can make turns to the left easier than they can to the right. Some people believe that this is related to the Coriolis effect. Is it? If it is how is it?


Replies:
Ralph B.,

Near the equator, the Earth travels 25,000 miles per day. Near Illinois, the distance is closer to 15,000 miles per day. When an object moves toward the equator, the ground accelerates eastward. This makes the object appear to accelerate westward. When an object moves away from the equator, the reverse happens. For something as large as a rotating tropical storm, this Coriolis effect decides the direction of rotation: clockwise in the northern hemisphere, counter-clockwise in the southern hemisphere.

The Coriolis force is a very weak force. For something as small as a motorcycle, forces such as and friction with the road would definitely overpower it. A very slight breeze from the side would have extreme effect compared to the Coriolis force. Check to see whether your motorcycle tends to fall to the left when standing still. If so, then the motorcycle is slightly heavier on the left side. This could cause the preference to turn left.

Ken Mellendorf
Math, Science, Engineering
Illinois Central College


I think the Coriolis effect is much too small to have a significant effect on the turning direction of a motorcycle. It is a "apparent" change in the trajectory of an object that results because the Earth rotates during the time lapse of an object. If you search Google for "Coriolis effect" you will find numerous "hits" that provide good detailed analyses.

The "right" vs. "left" thing -- could it be that it is simply the radius of curvature of the turns? For a right turn the cycle turns into the close lane whereas in the case of a left turn the cycle turns into the far lane. The right turn has a smaller radius of curvature so it would be reasonable that the right turn would be more difficult. The "northern" vs. "southern" hemisphere would need a large sampling of riders and careful statistical sampling or instrumentation to determine whether this is just a perception or involves "real physics".

Vince Calder


I am not sure what effect the Coriolis force has on turning, except that it is quite small. The Coriolis force on an object of mass m moving at speed v while at latitude L is given by

F = 2 m v w sin(L)

where w is the angular speed of rotation of the earth. For a bike of weight 1000 lb moving at 60 MPH at 40 degrees of latitude (near Philadelphia), the force is about 1/4 pound. Not noticeable, I would think.

The direction of the force in the northern hemisphere is to the right. I cannot think how this would make it easier to turn to the left. I suspect it is easier to turn to the left since all race tracks, by tradition, I suppose, have been constructed so the racers turn to the left.

Do you know for sure that bikers in the southern hemisphere find it easier to turn to the right? How are the race tracks constructed in the southern hemisphere?;

I would bet that race tracks in the southern hemisphere are also constructed so the racers turn to the left. I would further bet that bikers in the southern hemisphere find it easier to turn to the left. But I certainly do NOT know; it could be an interesting and rewarding area for some research. Let me know what you learn!

Best, Dick Plano, Professor of Physics emeritus, Rutgers University



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