曲臂内有将遮阳篷展开的大拉力弹簧。

A large tension spring which is unfolded in the curved arm.

youdao

往下拉这儿的话,会产生向上的拉力,中间有根弹簧,它能帮助你测出力的大小了。

And if you have a pull down here and you have a pull up here and you have in here a spring then you see you have a way of measuring that force.

youdao

再以质量m2的物体做同一个实验2，弹簧伸长相同，可知拉力相同，这与悬挂物体的质量，无关？

Now I replace this object by mass m2 but the extension is the same, so the pull must be same the spring doesn't know what the mass is at the other end, right?

youdao

You cannot have a spring pulled only at one side, because then it will then accelerate with infinite acceleration in that direction.

你不可能对弹簧只施加一边的拉力,因为那样的话弹簧就会以无穷大的加速度加速,就在这个方向上

耶鲁公开课 - 基础物理课程节选

So springs are always pushed or pulled on either side with the same force.

所以弹簧两边永远都是受到,相同的压力或拉力

耶鲁公开课 - 基础物理课程节选