Physics specific q

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21

<p>hmm... well i'll list what i know and see if i can pull an answer to that one out of my magic hat....</p>

<p>The negative charges repel eachother with Electrical Force, based on Faraday's law. F = ke * (Qq/r2)</p>

<p>The wires attract due to magnetic force... i think. The moving charge (aka current) through the wires produces the magnetic field. </p>

<p>now from here i am not exactly sure where to go. I understand your question about the relative speed of me to the charge etc, and how if it has no relative speed to me (because i am walking with it) it should appear stationary. If it were indeed stationary there would be no magnetic forces/field produced because that only comes from moving particles. But where i am confused is because i was under the impression that you can never actually follow the speed of the electrons which all move randomly, you can only track the drift speed which moves quite slow. If the drift appeared to be stationary it wouldnt necessarily imply that the electrons themselves had ceased their motion</p>

22

<p>fignewton that doesn't work. if your force is always tangential to the circle you will in fact not travel in a circle. Force = mass*acceleration and the only way you can accellerate in circular motion is with centripetal (center-seeking) force. Your velocity will always be tangent to the circle, but the force itself will not be</p>

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<p>"Work can be zero even when there is a force. The centripetal force in uniform circular motion, for example, does zero work because the kinetic energy of the moving object doesn't change"
Mechanical</a> work - Wikipedia, the free encyclopedia</p>

<p>Think about it: W = delta KE.</p>

<p>Work is only done if you are rotating the box faster and faster (aka accelerating and changing the speed).</p>

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<p>I dont believe work is done--you land up in the same place you started...</p>

25

<p>Assume that another force is keeping the crate in the circle.</p>

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<p>If that is the case, then the tangential force will only serve to make an increase in the speed of the crate. In that case, you will be doing work. </p>

<p>Perhaps you're getting confused because of friction. If there is friction, then your force will do work in order to counteract the work done by friction.</p>

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<p>so i guess that would be a rocket tethered to a string. i'll think about it</p>

28

<p>Yes, the rocket on a string going faster and faster around a circle is a great example of W > 0, total displacement = 0 (assuming the string is strong enough to provide the ever-increasing centripetal force). The string does no work, but the rocket engine does (it provides a purely tangential force).</p>

<p>Good luck tomorrow!</p>

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<p>No one answered? That's a great question.</p>