Calculating starting/tractive force

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Discussion Overview

The discussion centers on calculating the force required to overcome inertia and friction for a sliding door weighing 1500 lbs, which rolls on four wheels. Participants explore the effects of friction and acceleration over a specified time period, involving both theoretical calculations and practical considerations.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant calculates the force needed to accelerate the door to 0.25 m/s over 4 seconds, initially omitting friction, arriving at a force of 417 N (93.74 lbs).
  • Another participant suggests that resistance due to friction should be calculated as the weight of the door multiplied by the coefficient of friction, indicating that additional force is necessary.
  • A question is raised about how to consider the distribution of load across the four wheels, with one participant suggesting that it might not significantly affect the overall frictional resistance.
  • A later reply provides a formula for the total force needed, incorporating both friction and inertia, and corrects the mass conversion from pounds to kilograms, suggesting a total force of 176 N (40 lbs) based on their calculations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact calculations or the treatment of friction and load distribution across the wheels. Multiple competing views on how to approach the problem remain evident.

Contextual Notes

There are unresolved assumptions regarding the distribution of weight on the wheels and the exact method for calculating frictional resistance. The conversion between units (pounds to kilograms) is also a point of contention.

Who May Find This Useful

This discussion may be useful for individuals interested in physics, engineering, or mechanics, particularly those dealing with forces, friction, and motion in practical applications.

snwright
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Hey all-

First post here!

I need to calculate the force required to overcome inertia of a 1500lb object. It's a sliding door, which rolls on 4 identical wheels, each with a coefficient of friction of .02. I'd like to make it accelerate to .25m/s over a period of 4 seconds.

I think what I need OMITTING FRICTION is: F=Ma = 6672 N * .0625m/s2 = 417 N = 93.74 lbs. Is that accurate? How do I include the resistance due to friction?

thanks!

Spencer
 
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Resistance due to friction is weight of door times coefficient of friction. You need that much additional force. Be careful about how you consider the four wheels.
 
How should I be considering them? The load should be distributed pretty evenly across all four wheels. I was thinking that it would be a wash, and that the accumulated drag would be .02.
 
You need to add all the resistance forces to the inertia. The force needed would be:

F = 0.02mg + ma = m (0.02g + a)

g is 9.81 m/s² and the SI unit for m is kg not N (So 1500 lb is 680 kg). F = 176 N = 40 lb.
 

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