# Moving Pendulum

1. Feb 24, 2007

### anantchowdhary

When a pendulum is moving

will the length of the string that the bob is attached to appear to be contracted?I have this doubt as the string is sometimes in direction of motion and at one point absolutely not in the direction of motion

2. Feb 24, 2007

### Hootenanny

Staff Emeritus
Appear to be contracted from whom's point of view?

3. Feb 24, 2007

### anantchowdhary

From an observer's point of view whoo is in an inertial frame.If he wants to calculate the time period of the pendulum,how will he measure the length as it changes from position to position

4. Feb 25, 2007

### anantchowdhary

5. Feb 25, 2007

### anantchowdhary

Please sum1 help me out here!

6. Feb 25, 2007

### pmb_phy

Each infinittesimal portion of the string is a linie segment which is moving perpendicular to its motion. According to SR the length of the string will remain unchanged.

Pete

7. Feb 25, 2007

### Staff: Mentor

I assume that the OP meant that the swinging pendulum was in a moving rocket (say) being observed from the earth.

8. Feb 25, 2007

### pmb_phy

That's the usual way. Another way is to to have a charged particle on a string at a fixed distance from a charged plate. But you're right, he was probaby speaking of in a grav-field or in a rocket shift.

Pete

9. Feb 25, 2007

### anantchowdhary

No,i just meant to have an experiment of a pendulum,moving at a constant velocity relative to a frame.Now the string of the pendulum,once is perpendicular to the direction of motion,and when it is at its maxima,it has some component in the direction of velocity,so my question was,wouldnt this affect the length of the string?

Also the time period as viewed from another rest frame would be the
$$T = \gamma T_0$$?

where T is the time period as viewed by the rest frame and $$T_0$$ ,$$T$$the time period as viewed by the moving frame.

Last edited: Feb 26, 2007
10. Feb 26, 2007