A metal ball is attracted by 2 rows of pemanentmagnets, the ball roles up a small ramp because each magnet is a bit closer to the center of the ramp. The magnetic field at the end of the ramp is not strong enough to prevent the ball from falling off the ramp. It effectively drops out-of the magnetic field.
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The ball rolls up the ramp while being attracted to the 2 rows of magnets. This causes the ball to become a magnet it self. As both sides of the ramp are of the same polarity both sides of the ball will become the same other polarity. The ball being slightly magnetised at the beginning of the ramp has 2 north poles and 2 south poles. BUT when it moves up the ramp the field intensity increases the flux grows exponential (the ball is even moving) So in stead of 4 poles the ball now becomes a magnet with only 2. This causes the attraction at one side of the ball to fail and allows the ball to drop out of the fields