What about the component of Newton's Law in the radial direction?

Recall that the bob doesn't move in the radial direction. This means that the tension T in the rod must balance the radial component of the force due to gravity and the radial acceleration of the mass. Use Newton's Second Law


to solve for the tension in the rod. Start by finding in terms of , m, and g in the little quiz below. Recall the figures on the Undamped Math Model Concepts page.

What is Fr?

It can be shown that the radial acceleration is given by


Now substitute these expressions for and into the equation and solve for T.

What is the tension in the rod?