• University of South Carolina

• PHYS 201 

Cycle 3: Uniform Circular Motion

Physics 201L Thursday 6:45-8:45
 
Abstract
According to Newton’s second law as it applies to an object in uniform circular motion,
an object that is in uniform circular motion will be acted upon by a net force that points towards
the center of the circular path. This force is called centripetal force, and this force has a
corresponding centripetal acceleration. The purpose of this experiment was to observe Newton’s
second law using a metal bob attached to a spring apparatus that could be rotated at four
experimental radii of rotation to determine a linear fit.

Introduction
Newton’s second law for an object in uniform circular motion states that when an object
experiences uniform circular motion, net force exists that acts upon the object. This net force
points toward the center of the circular path. Newton’s second law also states that the force is
equal to the mass multiplied by the acceleration. In uniform circular motion, the acceleration is
the centripetal acceleration, or ac, making the force Fc. This centripetal force is perpendicular to
the velocity and points in the direction of the center of the circle. If there is a larger force, the
radius will be smaller. The purpose of this experiment is to examine the relationship between
acceleration, mass, and force within uniform circular motion. The mass of an object in uniform
circular motion can be determined by using F=ma.
Procedure
First the mass of the bob was recorded using a triple bean balance. The bob was
reattached to the apparatus. The apparatus was spun and the bob and spring were observed. The
radius of rotation was measured from the axis of rotation to the point at which the central tip
touched the bob. A piece of paper was placed at the radius to better observe the tip hit during
rotations. A stopwatch was used to time the amount of time it took for the bob to hit the radius
for fifteen rotations. This was repeated for four experimental radii with the times recorded. Each
set of fifteen rotations was repeated three times. To determine the average period, the average
time was divided by 15. The acceleration of the bob for each radius was calculated. The force
causing each acceleration was calculated.