# Calculating starting/tractive force

1. Jun 23, 2011

### snwright

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

2. Jun 23, 2011

### obafgkmrns

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.

3. Jun 23, 2011

### snwright

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.

4. Jun 23, 2011

### jack action

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.