Speed of a wave in a string is given by √(τ/μ) . But this speed is with respect to which reference frame? Since, the speed depends on τ and μ( which are independent of reference frame ), I can consider speed of wave independent of reference frame. But this is not so. From experiment, we know that if the Speed of a wave in a string is v = √(τ/μ) with respect to string ,then with respect to a reference frame moving with speed v with respect to string along the direction of wave propagation, the wave's speed will be 0 m/s. So, experimentally , I can't consider speed of wave independent of reference frame. Can anyone please resolve this contradiction?