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Even if every possible attempt to avoid stuff that can be avoided (like it will topple, the connectors will break, it won't overcome the rolling resistance, etc, etc) is made

What if one of the magnet was replaced by iron or something?

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  • $\begingroup$ Nothing wrong. It can be only tow with a third magnet $\endgroup$ – Alchimista Dec 8 '17 at 14:09
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    $\begingroup$ Now, the donkey and carrot setup will work if the donkey is hungry enough. $\endgroup$ – Lambda Dec 8 '17 at 15:27
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Remember Newton's third law, which slightly re-stated goes "Everything that exerts a force also experiences an equal and opposite force."

The left magnet is pulled or pushed with some force $F$ by the other one, which experience the opposite force $F$. They stay in place because they are held by the struts in the car. So the struts holding the magnet experience the force the magnet experience, and exert an equal counter-force... which means that the magnets will not be accelerating (they are held still). But now the struts will exert forces on the parts of the car holding them, and so on. As you go around the loop this sums to zero: every part is safely held by other parts so that the forces balance. So the net force on the entire car is zero: it will not accelerate.

(Same thing with iron rather than a front magnet)

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  • $\begingroup$ If one magnet was not attached to the car, that means it could move? $\endgroup$ – Rick Dec 8 '17 at 14:27
  • $\begingroup$ If one magnet was attached to the car and the other was fixed to the ground, then the car would either move toward or away from the fixed magnet (depending on polarity.) OK, So now you have found a way to make a car move a few inches. Then what? $\endgroup$ – Solomon Slow Dec 8 '17 at 15:06

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