This is a simulation of motional emf. The red rod can slide without friction on the blue rails. A constant force (in red) is applied on the rod to the right. We might think that that would result in motion with constant acceleration to the right, but that's not what we see. One key is that there is a uniform magnetic field directed into the screen.
As time goes by, we see that a resistive force (in orange) to the left gradually builds up, until the rod reaches a constant velocity. We call this a terminal velocity. The resistive force come about because the rod, rails, and the green resistor and black wires on the left make up a complete conducting circuit. Moving the rod to the right increases the magnetic flux through that loop, giving rise to an induced current in the loop that acts to oppose whatever is making the flux change. The current experiences a force because of the field - this is the resistive force that acts against the motion of the rod.
The applied force is removed after 8 seconds - what happens then?
Simulation posted on 2-26-2018. Written by Andrew Duffy
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