Lab 4: Uniform Circular Motion
SP211: Physics I
Fall 2018
Dr. M.E. Jamer
1 Introduction
Uniform circular motion occurs when an object go es around in a circle at constant speed. Note
that although the object’s velocity is constant in magnitude, it is not constant in direction, and thus the object
is accelerating even though its speed is constant! Since the object is accelerating, there must be a net force on
it. One of our goals for this laboratory is to remind ourselves that the force on and acceleration of an object
traveling in a circle with a constant speed are inward, i.e., toward the center of the circle. We will determine
the magnitude of the inward (centripetal) acceleration experimentally and then multiply it by the mass to cal-
culate the magnitude of the required centripetal force. We will then attempt to show that, for this experiment,
the force responsible for centripetal acceleration is provided by a spring. The tension in the spring is equal to
Fspring =mac. For the rotating machine we will use in this exercise, we can measure the mass of the plumb bob
and the orbital radius directly. We can measure the period of revolution by using a stopwatch to measure the
time required for 10 rotations, and then we can calculate a measured value for the tangential speed, velocity, and
the centripetal acceleration (ac). We can measure the tension in the spring by measuring the weight required to
stretch the spring to the same degree it was stretched while the system was rotating.
2 Procedure
2.1 Measure the Bob Mass
1. Measure the mass of bob using an electronic balance.
Mass =
1
