ðɪs ɪz ˈoʊnli tɹˈuː ɪnðə nˈɑːnɹˌɛləɾɪvˈɪstɪk lˈɪmɪt, ænd ˌʌndɚpˈɪnz ðə pɹˈɪnsɪpəl ʌv ˌɑːpɚɹˈeɪʃən ʌvðə sˈaɪklətɹˌɑːn.
This is only true in the non-relativistic limit, and underpins the principle of operation of the cyclotron.