View Single Post
Old 07-27-2009, 07:30 PM   #310
Erick Mead
 
Erick Mead's Avatar
Dojo: Big Green Drum (W. Florida Aikikai)
Location: West Florida
Join Date: Jun 2005
Posts: 2,619
United_States
Offline
Re: Is It Missing In Everybody's Aikido?

Quote:
David Skaggs wrote: View Post
I use vector meaning a force with a direction and magnitude. To walk a refrigerator I would use a force that can be broken down into several vectors. If I place my hands high enough on the refrigerator I can use the structure of the refrigerator as a lever. One of the vectors would be vertically up and another would be horzntally away from me. These two vectors would tilt the refrigerator's top away from me and lift the bottom of the refrigerator nearest me off of the floor reducing the surface area the refrigerator has with the floor thus reducing the amount of friction needed to overcome. Another vertical vector on one side would tilt the refrigerator more so that it is now balanced on one corner. An additional vector would be a horizontal one to one side of the refrigerator to rotate the refrigerator moving the free corners, beginning the walk.
Keying off Sy's pet peeve -- what you described was actually not using leverage -- Why? Because there was no fixed fulcrum. If you set up a lever and the 'fulcrum' can move (or fail) that tendency to move defines a shear -- it is moving in shear if it is hinged. If it were, say a pencil as our lever, the shear is the stress that breaks the pencil. Your assumption is that the opposite edge of the fridge IS the fulcrum, and it isn't -- not any more than the opposite side of a large rock still resting on the ground after you lever it with a stick on a smaller rock as fulcrum. By setting a fixed leg triangle with a connecting hinge at the top and then shortening the base fixed length, you lift the fridge onto one edge -- in shear.

Quote:
David Skaggs wrote: View Post
A cycle of the car moving back and forth until there is enough momentum to unstick the car from the mud.
The swing would be similiar. It needs an initial force to get it swinging an additional pulses of force to increase the swing's movement.
All the swing needs its gravity and a clever moving fulcrum suspended from it. In other words it is a double pendulum.
By altering the position of the CG in the seat (the effective fulcrum in this scenario) with regard to the line of suspension, gravity causes it to swing into line with the altered CG. The moving fulrcum identifies a shear which is coverting action of gravity into a different axis. If resonance is achieved (where the CG shift occurs at a zero velocity cusp ( the peak of swing) then the system can be driven to its dynamic structural limits (which may or may not be more than the material structural limits.)

Cordially,

Erick Mead
一隻狗可久里馬房但他也不是馬的.
  Reply With Quote