View Full Version : forces

Ulrich Simon
12-20-2000, 07:08 AM
Dear all,

I enjoy the discussion on centrifugal forces and like to
give some additional remarks.

1. Forces:
Forces are axiomatic.
They all CAN'T be measured directly. We have to measure
effects from what we named forces.
So they are all a kind of virtual.

2. The Cut:
"No force without a cut and no cut without forces"
Forces replace the actions from parts that we don't want to
draw in.
Gravity? We can say that we cut off the earth.

3. D'Alembert:
Inertia (acceleration, centrifugal, gyroscopic forces) IN
the free body diagram?
Here we can think that we cut off the body's mass and
replace it's effect with a force.
We keep only the rigid structure in the diagram.

4. Equilibrium:
Then there is no difference between all the forces in
principal. They are all "real" or not.
We can use (and think) the equation of the dynamic
equilibrium in the way: 0 = m*a + ...
.. but we don't have to.

Good forces to all of you

Ulrich Simon

Institut fuer Unfallchirurgische Forschung und Biomechanik
Universitaet Ulm, Germany
Web: http://www.biomechanics.de

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