走一圈回到起点，平均速度为零就等于没走吗？

Measures of distance moved are thus defined as the total distance travelled, where the change in displacement is the change in position that includes the direction between these two positions.

[latex]v=\dfrac{\Delta d}{t}[/latex]                           [latex]\vec{v}=\dfrac{\Delta\vec{d}}{t}[/latex] Where... [latex]v[/latex] is the speed, commonly measured in metres/second (m/s) or kilometres/hour (km/h) [latex]\vec{v}[/latex] is the velocity, commonly measured in metres/second (m/s) or kilometres/hour (km/h) and includes a direction [latex]\Delta d[/latex] is the distance travelled, commonly measured in metres (m), kilometres (km) [latex]\Delta\vec{d}[/latex] is the change in displacement, commonly measured in metres (m), kilometres (km) and includes a direction [latex]t[/latex] is the time, commonly measured in second (s) or hours (h)