2 magnets disk on a axle
4.5 Volts 2Amp
2 aluminum bands on plastic
The Laplace rail is a good demonstration of the ‘right hand curl rule’
Using a hand as a guide If we have a current moving in the direction of the thumb, the magnetic field will be oriented in the direction of the curled fingers
When the current is applied the only way for the circuit to be completed is through the axle. Given the red terminal is positive the current is moving from left to right through the axle generating a circular magnetic field that is oriented towards the viewer.
The magnets on each end of the axle are now repelled by the field generated by the current and force the axle to move. If you were to switch the terminals the axle would move towards the viewer - this is demonstrated in the later half of the video which can be found here.