Bifilar pendulum questions for my lab

[jenil_nz]

hi,
i am doing an investigation in my physics class. its about bifilar pendulm.the aim of the investigaton is what thngs affect the period for one swing of the pendulum. so the the variable i changed for measuring the period was the length of string. now i have got my results but the only thing I am not sure about this is what's the equation for the period & length of the string & wat other physics is involved in the pendulum(torque,tension etc...)
if any1 know anything about this, then please help me out.

 

[kuruman]

The expression for the period of the bifilar pendulum is the same as the sinfle string pendulum $$T=2\pi\sqrt{\frac{L}{g}}$$ Of course here $L$ is not the length of the strings but the vertical distance from the point(s) of support to the horizontal level of the swinging mass.

 

[Mister T]

now i have got my results but the only thing I am not sure about this is what's the equation for the period & length of the string & wat other physics is involved

Can you show us your results? That way we can guide you towards your next step.

 

[bob012345]

The expression for the period of the bifilar pendulum is the same as the single string pendulum $$T=2\pi\sqrt{\frac{L}{g}}$$ Of course here $L$ is not the length of the strings but the vertical distance from the point(s) of support to the horizontal level of the swinging mass.

How is that different from the string length? Which mode of oscillation are you referring to?

 

[Mister T]

How is that different from the string length?

$L$ is the distance from the axis of rotation to the center of mass of the pendulum bob.

Which mode of oscillation are you referring to?

There's only one mode for this oscillator. Meaning it only swings back and forth. It's a simple pendulum.

 

[bob012345]

$L$ is the distance from the axis of rotation to the center of mass of the pendulum bob.There's only one mode for this oscillator. Meaning it only swings back and forth. It's a simple pendulum.

These pendulums are used to measure the moment of inertia of objects and they oscillate in the horizontal plane in that case, not in the vertical plane.

Also, note that the OP is from 2005.

 

[kuruman]

How is that different from the string length? Which mode of oscillation are you referring to?

Imagine a "V" suspension with the mass at the apex. The length of the pendulum is the height of the isosceles triangle. The "V" suspension better constrains the pendulum motion in a vertical plane. THis is useful when making speed measurements at the lowest point of the motion using a photogate. The path of the bob that breaks and unbreaks the photogate beam needs to be perpendicular to the beam.

Yes, the OP is from 2005. Greg has tasked us with replying unanswered threads that receive Google hits to raise our profile.

 

[bob012345]

Imagine a "V" suspension with the mass at the apex. The length of the pendulum is the height of the isosceles triangle. The "V" suspension better constrains the pendulum motion in a vertical plane. THis is useful when making speed measurements at the lowest point of the motion using a photogate. The path of the bob that breaks and unbreaks the photogate beam needs to be perpendicular to the beam.

Yes, the OP is from 2005. Greg has tasked us with replying unanswered threads that receive Google hits to raise our profile.

I have seen the term bifilar pendulum to refer to the situation with two separate strings not meeting at the CM and the pendulum is oscillated around the vertical axis in the horizontal plane. Then the period is a function of the moment of inertia.

 

[kuruman]

Yes, that's the torsional bifilar pendulum. However OP is referring to swings which implies motion in a vertical plane not rotations about a vertical axis. Here is the interesting hybrid of "Y" suspension that provides a good basis for an experimental investigation of pendulum motion.

 

[phinds]

Can you show us your results? That way we can guide you towards your next step.

The OP hasn't been here in 16 years so I doubt you'll get an answer.