The value<span> of </span>y<span> has changed at a </span>much<span> greater rate. </span>If<span> the x-axis represents time and the </span>y<span>-axis distance, as is the case in </span>many<span> applications, then the rate of </span>change<span> of </span>y<span> with respect to x -- of distance with respect to time -- is called speed or velocity.</span>
