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A pendulum hanging from ceiling of an accelerated container if viewed from inside it would be deformed and make some angle with its normal position(at rest). We can explain this deformity using the concept of pseudoforce.

However if we look at it from outside the container would the pendulum still appear deformed? If yes how would we explain the cause of this deformity and calculate the angle it makes with the normal to the ceiling

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  • $\begingroup$ Well, if the pendulum is attached to the accelerating container, it is accelerating as well. According to the second Newton's law, if the object is accelerating, the net force acting on it is non-zero. In this case you only have one force (except for gravity) - the one acting on the pendulum at the point of attachment to the container. This force makes the pendulum accelerate. Provide a pic, if you want a more detailed answer. $\endgroup$ – mavzolej Apr 16 at 3:36
  • $\begingroup$ My question is not to ask whether the pendulum will accelerate or not. If the container is accelerated towards right the pendulum will shift towards left making some angle with the normal to the ceiling ( if viewed from non inertial fram of reference) and this can be well explained using the concept of pseudoforce. But if it is viewed from outside the container, will it appear to be tilted. If yes then why?.In which direction and by what angle? $\endgroup$ – Ritu Khanna Apr 16 at 10:15
  • $\begingroup$ Yes, because the container will apply the force at the attachment point. This force changes the pendulum's angular momentum. The angle is same as in the container's reference frame. $\endgroup$ – mavzolej Apr 16 at 14:58
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The pendulum bob must have the same acceleration horizontally as the container. This is can be explained by the constraint of length of the string, i.e., if the pendulum bob remained at the same position and the container moved forward, then the string length would continuously increase, which is not possible. With respect to an observer in an inertial frame outside the container, the only forces on the bob are it's weight and string tension. Only string tension can provide the necessary horizontal acceleration, and for that the string must be tilted at some angle with the vertical.

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