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I saw a statement in my HC Verma's physics book.

One should take smaller steps while walking on ice since it ensures smaller friction force.

Now let us say there is a man M of mass 50kg standing on ice and the maximum distance he could cover in a single step without slipping is 15cm.

Now an observer A (who is at rest) observes that the man moves $10\;cm$in $1 \;sec$ in a single step. So for him he doesn't slip and simply manages to move $10\;cm$.

If the same person is observed from a frame B moving with $10\;cm/s$ in the opposite direction of what M's motion is according to A then for B, the man M moves $20\;cm$ in $1 \;sec$ and this distance is also covered again in a single step (which is quite obvious) but this means that for B the man M should seem to fall down but this will break the symmetry between the two inertial frames .

So what's wrong with this experiment ? Can't we use this technique to distinguish between two inertial frames ? Why/ why not ?

Ankit
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2 Answers2

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The point is that the ice is moving in one frame and not in the other. Classically, the speed of the man relative to the ice is the same in any inertial frame.

Ankit
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Ben51
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Someone flying by the Earth in a rocket with constant velocity sees you, sitting at your desk, to be moving at a speed that is significant compared to $c$, yet somehow, you don't slip and fall. Whether or not a person walking on ice slips depends only on their motion with respect to the ice, so observer $B$ would not expect the man to slip based on his motion w.r.t. $B$, because his motion w.r.t. the ice is still the same.

Sandejo
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