Re: Pendulum acceleration

[Mark Sylvester <msylvest@XNET.IT>]

on At 22:04 23/10/01 -0500, Herb Schulz wrote:
> >Since gravity is what causes a pendulum to move,
> >neglecting air friction and differences in direction etc.,
> >will the bob experience the same magnitude of
> >acceleration though out it swing.  I want to know if the
> >change in speed is the same. Part of me says of course it
> >is, but a smaller part wants to say the acceleration is
> >greater at the bottom than at the top. I not sure my
> >equipment is sensitive to detect those differences.
> >
>
> Howdy,
>
> It is NOT gravity that causes a pendulum to swing; in the small angle
> approximation, it's the horizontal component of the tension in the
> string that makes the pendulum oscillate.
>
> Good Luck,
> --
> Herb Schulz
> (herbs@interaccess.com)

I've always found this way of analysing the forces conceptually poor.
Whether I'm about to use the small angle approximation or not, it seems
more to the point to consider the pendulum as moving along an arc of a
circle, with tangential velocity and acceleration components being of
interest. The tangential acceleration is g*sin(theta). The tension is
associated with a radial centripetal acceleration, being a radial force.

Mark


Mark Sylvester
UWCAd
Duino Trieste Italy