Pendulum With Force Scale

Purpose

To show the tension in the string exerted by a swinging pendulum.

Equipment

Pendulum with bifilar support, 40 N spring scale, 22 N (5 lb) weight.

Images

g1-18

Description

The spring scale reads the tension in the string as the pendulum swings, about 25 Newtons at the center and 19 Newtons at the ends of the swing with a bob mass of 1.1 kG. In this setup:◙F (center) = mg + mrw^2 = mg (3 - 2 cos a) ◙F(end) = mg cos a ◙where by conservation of energy ◙m v^2 /2 = m r^2 w^2 /2 = mgr (1 - cos a) ◙m r w^2 = 2mg ( 1 - cos a)