0
$\begingroup$

A body is attached to another with a string and both are in free fall. How does the tension in the string being zero make sense conceptually?

$\endgroup$
  • 4
    $\begingroup$ This question would become much more answerable if you told us why you think it doesn't make sense. $\endgroup$ – ACuriousMind Mar 22 at 18:56
  • 1
    $\begingroup$ Draw a free body diagram (including a tension force) for each mass and write N2L equations. If they are in free fall, you know they have the same acceleration, and it is $\vec{g}$. If there is tension which isn't zero, they can't have that acceleration. $\endgroup$ – Bill N Mar 22 at 19:09
  • $\begingroup$ because if you hold one body in your hands at the ground level - string will experience tension because other body will affect string with weight. And when on free fall both bodies have zero weight, thus - no force is applied to a string, and that's why you will get no tension. $\endgroup$ – Agnius Vasiliauskas Mar 22 at 20:10
2
$\begingroup$

@Bill N has shown you the analytical approach. Here is a conceptual approach that might help.

Think about a tug of war between two teams pulling on a rope. There is tension in the rope and the distance between the teams is constant. Now imagine you are in the middle of the rope and cut it. The teams will fly apart which confirms there was tension in the rope that kept them from separating.

Now imagine two objects attached by a string one vertically above the other with the string stretched out in free fall. The distance between the objects is constant. Now imagine you are also in free fall between the two objects. You cut the string. Will the distance between the two objects increase like in the tug of war? No, the separation will remain the same because the acceleration of each object, $g$, will remain the same. Conclusion: there was no tension in the rope.

Hope this helps.

$\endgroup$
0
$\begingroup$

If the tension were not zero then the objects would not be in free fall. Free fall means that there are no non-gravitational forces acting, and tension is a non-gravitational force.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.