Setup:
Suppose one has two identical wheels W1 and W2. Wheel W1 is rotating about its axis with angular velocity →ω while the other wheel is not rotating. Imagine then two identical carts C1 and C2 with the rotating wheel W1 inside C1 and the non-rotating wheel W2 inside the cart C2. Initially the velocity of both carts is →v1=→v2=[000]T.
Question:
Suppose that to both carts C1 and C2 is applied the same constant force →F for 1 second. After 1 second is the velocity of cart C1 slightly smaller then the velocity of cart C2?
Answer (...)
This is a question that I formed to test some understanding about relativity. I think the wheel W1 has a greater energy then the wheel W2 hence it has a slightly greater inertial mass, therefore the final velocity of cart C1 should be smaller then the velocity of cart C2! Is this correct?
I have never worked seriously with relativity, but if I take the notorious formula E=m⋅c2 and consider E1=12⋅I⋅ω2>0=E2 follows that the first wheel has the total energy E1t=m⋅c2+E1 before the cart was moving while and the second wheel has the total energy E2t=m⋅c2. When the the force is applied to the first cart, it tries to move a mass m1=m+E1c2>m hence cart C1 should have a smaller acceleration. PS: The second cart will gradually increase its translational energy hence its mass should also be increased, but assume the rotational energy of the former is much greater ... Is this reasoning correct?
Answer
Yes, this is correct. Energy increases inertia. Of course, in typical situations E1/c2 is much much smaller than the masses, which is why this effect was discovered theoretically and not experimentally.
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