This simulation shows a current loop in uniform magnetic field.
The black arrows show the force due to magnetic field on the loop.
\vec{F}= q \vec{v} \times \vec{B} or \vec{F}= I \int d\vec{\ell} \times \vec{B}
The magnetic field in in the +Z direction if Bz>0.
Then ,torque for the loop is calculated from definition \vec{\tau}=\vec{r}\times\vec{F}

Because the current flow in the same counter-clockwise direction.
The force on the loop change sign during each helf cycle.
If we current reverse direction during each helf cycle, the following device can turn into a motor.
A voltage source is needed in the loop to drive the current.

P.S. The above simulation did not include the induced emf due to changing magnetic field in the loop.

You are welcomed to check out a very good animation [url=]DC motor operation principle[/url]

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