I've been working on a lab for my electrical class, and I can't quite seem to find the answer. I have a DC motor that plugs into a 120V supply,from the supply it is connected to the shunt field, then to a switch (sw3), which either connects the armature to the supply/shunt field, or disconnects it from the supply/shunt field and connects it to a light bulb. Our first exercise was to simply unplug the motor after it is running at max speed, and time how long it takes for it to stop turning. This took about 5 seconds, as I assume the only braking torque is caused by windage and friction. My second exercise was to let it get up to speed, then switch sw3 so it disconnects the armature from the shunt field and connects it the to light bulb. I understand this is "dynamic braking" and it took ~3 seconds for it to stop spinning. The last exercise was to short out the light bulb, bring the motor to full speed, and then switch sw3 to the shorted light bulb. This stopped the motor almost immediately.
I have a few questions, I know the braking has to do with counter EMF, I'm just not sure exactly how/why it causes it to brake so much quicker without the resistance of the light bulb. I'm also not sure if both exercise 2 and 3 would both be considered dynamic braking? Thanks a lot for the help!