# Pendulum - How it affects gear train torque?

1. Jun 2, 2013

### jryer

Does the gear train in a classic weight driven clock see a torque decrease when we lengthen the pendulum?

thanks guys for your help - (inventor question)

2. Jun 3, 2013

### jbriggs444

Are you asking this as a physics question or as a design question?

The physics version would be: "How would lengthening the part of the pendulum below the pivot point change the torque delivered by the escapement"

The design question would be: "How would lengthening the part of the pendulum below the pivot point change the torque required from the escapement".

3. Jun 3, 2013

### jryer

The first one - "How would lengthening the part of the pendulum below the pivot point change the torque delivered by the escapement; would it increase or decrease?"

Also, I'm assuming the change in the torque delivered is transferred (seen/realized) to the gear train, is this a correct assumption?

4. Jun 3, 2013

### jbriggs444

Possibly we are still speaking at cross-purposes.

To my way of thinking, the pendulum is a driven oscillator. It does not apply torque to the gear train. The gear train applies torque to it. In the absence of any applied torque, it would continue move back and forth in an arc that slowly decreases over time due primarily to air resistance.

The gear train has to provide enough torque to overcome the losses due to air resistance. But it must not provide so much so that the pendulum's arc increases too greatly. [The escapement assures that this torque is applied in proper synchronization with the pendulum's motion].

So my answer is that the torque applied by the gear train/escapement on the pendulum is unchanged by the length of the pendulum. From Newton's third law, the torque applied by the pendulum to the escapement/gear train is also unchanged.

5. Jun 3, 2013

### jryer

JBriggs, take a look at this link