# Electric Motor Assignment Angular Velocity Question

1. Feb 21, 2015

### spinflick

1. The problem statement, all variables and given/known data

Hey so I've made a motor that looks and works exactly like the one in this video

The assignment is asking me how I would go about finding the angular velocity, specifically " Analysis of the energy changes involved in the motor to work out the speed/ or angular velocity"

The problem is I have no idea how to do this, I asked my physics teacher and he said start from F= B I L sinθ but its been very confusing, I think I may not have some of the values I need and even if I did I'm sure its not as simple as just substituting them into the equation.

Motor runs off a battery of 12 V, 1.3 amps. It has 120 coils of copper wire (estimate) and the angle for sinθ is 90 degrees

2. Relevant equations

F= B I L sinθ

3. The attempt at a solution

I don't know which values I need from the motor. I run it off 12V and a 1.3 amp battery, I have a multi-meter and a spring balance, I don't know the magnetic field strength of my magnets or the electromagnets I've made. I forgot to count the amount of coils, but the teacher marking it isn't going to know either so I'd estimate around 120 coils. If anyone can help me out it'd be great, ask me for information about the motor and I'll be happy to get the values for current, voltage, resistance etc and reply back

2. Feb 21, 2015

### Suraj M

Ok I'm not sure but can't you just record the time for 20 rotations, divide by 20 to get time period $T$
then substitute in the equation for $\omega$. Wouldn't that make sense? I'm sorry if i'm wrong!

3. Feb 21, 2015

### spinflick

That's helpful, and it should get me the angular velocity, so ill use my phone and slow motion record it and count. Only thing from that point is what 'energy changes' in the motor give me that amount of velocity

4. Feb 21, 2015

### Suraj M

I dont know much about current, but if i were you i would find the moment of inertia $I$ and then calculate Rotational kinetic energy.