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Re: [Phys-l] Equations (causal relationship)



Well... I think "controlling the car's acceleration and letting the car figure out the force" is a big stretch.

I control the "gas pedal." Depressing it further "instructs" the engine to increase its torque, and the increased torque gets transmitted into a forward force by the drive wheels. If I see the acceleration is inappropriate, I adjust the force (via the gas-pedal, engine torque, wheel-road force) to change the acceleration accordingly.

It sure seems clear to me I am increasing or decreasing the force in order to get the acceleration I want.

* * * Different point * * *

One thing that was mentioned once, and then dismissed because the person didn't distinguish "net force" from force, was the idea that forces can exist without acceleration, but acceleration cannot exist without force.

This bothered me that the person was brushed off so quickly.

Although it sometimes takes a while, I think students eventually get the idea that we have to find the net force in order to calculate the acceleration, or that we can use the measured acceleration to find the net force. But what about those cases for which is it clear there are forces presnet but the net force is zero. These are examples of forces clearly existing without acceleration.

I think that if forces can exist without acceleration, but acceleration cannot exist without forces, students will view the force as more fundamental and/or the net forces can be the cause of acceleration. I thinks it's hard to say that acceleration can be viewed as the cause of forces when it is clear forces exist without acceleration.

I think the person who first mentioned this got pushed aside on a technicality.

Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu