<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (April 2009) (Learn how and when to remove this template message) </Td> </Tr> <P> A bob is the weight on the end of a pendulum found most commonly, but not exclusively, in pendulum clocks . </P> <P> Although a pendulum can theoretically be any shape, any rigid object swinging on a pivot, clock pendulums are usually made of a weight or bob attached to the bottom end of a rod, with the top attached to a pivot so it can swing . The advantage of this construction is that it positions the centre of mass close to the physical end of the pendulum, farthest from the pivot . This maximizes the moment of inertia, and minimises the length of pendulum required for a given period . Shorter pendulums allow the clock case to be made smaller, and also minimize the pendulum's air resistance . Since most of the energy loss in clocks is due to air friction of the pendulum, this allows clocks to run longer on a given power source . </P> <P> Traditionally, a pendulum bob is a round flat disk, lens - shaped in section, but bobs in older clocks often have decorative carving and shapes characteristic of the type of clock . They are usually made of a dense metal such as iron or brass . Lead is denser, but is usually avoided because of its softness, which would result in the bob being dented during its inevitable collisions with the inside of the clock case when the clock is moved . </P>

Does the weight of a bob effect a pendulum