Education Technology

Circular Motion

Published on 10/19/2005

Activity Overview

In UCM, the net force called Fc is equal to mv2/r and is directed toward the center. This is demonstrated by an object that is suspended by a string and is moving in a circular path which makes a conical pendulum. In this experiment, you will measure the tension and the length of the string to show that net force, Fc = mv2/r.

Before the Activity

Preliminary Activity

  • Draw a free-body diagram that act on a conical pendulum.
  • Show the y and x components of the tension (T) on the string. Label the angle between the tension and the vertical.
  • Does the dove accelerate in the vertical direction
  • What does this tell you about the magnitude of the vertical component of T and mg?
  • Does the dove accelerate in the horizontal direction
  • Since the net force in the radial direction for objects in UCM is the centripetal force, what does this tell you about the horizontal component of T and mv2/r?
  • During the Activity


  • Select 10N on the dual force sensor.
  • Hang the dual force sensor on the ceiling.
  • Connect the force sensor to channel 1 of the CBL™
  • Turn on the calculator and go to apps then DATAMATE™.
  • The main screen should show CH1 Force (N) on top and a force reading on the right hand corner.

  • Next you will zero the sensor.
  • Select setup from the main screen.
  • Select zero from the setup screen.
  • Select channel 1 from the select channel screen.
  • With the force sensor hanging on the ceiling, a 0 reading or about 0.024 will register on the right corner of the main screen.
  • Suspend the dove on the hook of the dual force sensor. Get the weight of the dove and record your data.
  • Measure the height from the point of suspension to the estimated center of mass of the dove. This is the length of the string (L).
  • Set up the dove by turning on the switch attached to its body. Wait for it to fly in a stable circle in 15 seconds or so.
  • Once the dove is up and flying in a circle of constant radius, measure the height (H) from the ceiling using a meter stick.
  • Select start on the main menu. Get the 3 highest force values from the graph.
  • Repeat to make 3 trials and get the average tension of the string and its height.
  • Data: Weight of dove __________N Trials Tension (T) in N Length (L) in m Height (H) in m 1 2 3 Average

    After the Activity

    Questions and Analysis
    1. What techniques for measuring radius and angle would you recommend for best? 2. Calculate the tension on the string from Ty = mg and Tcos?. 3. a) what is supplying the centripetal force to keep the dove flying in a circle? b) How do you measure the doves' velocity? Use the calculators' math (solver) function. 4. What do you conclude about the direction of the net force that keeps the flying object in UCM? 5. How does the dove overcome air friction? 6. List sources of error.