HOWARD UNIVERSITY
COLLEGE OF ARTS AND SCIENCES
COMPREHENSIVE SCIENCES PROGRAM
PHYSICAL SCIENCES
EXPERIMENT 2 (COMPUTERIZED VERSION)
THE LAW OF THE PENDULUM
NAME: ____________________________ ID#: ___________SECTION: ____ DATE: _____
INTRODUCTION:
A simple pendulum consists of a small heavy mass attached to a light string suspended from a rigid
support. The pendulum is set swinging by displacing the mass (called the bob) slightly and then letting go. Make
sure the bob has an unobstructed arc in which to swing. Figure 2.1 illustrates the proper displacement of the bob
and the swinging arc for a simple pendulum. The 'simple' is used to describe the pendulum because most of the
mass is concentrated at a point (the bob). The system we will be using today is not ideal because there is some mass
distribution within the bob and we are not accounting for the mass of the string. The system does, however, allow
us to closely approximate the Period of a pendulum.
The period of a pendulum is the time required for one swing of the bob and can be calculated using the
formula:
T  2 L
g
Equation 2.1
'T' is the term used to represent the period in seconds.
'L' is the length of the pendulum, in cm.
'g' is the acceleration due to gravity and is a constant with a value of 980 cm/s2 for this experiment.
Figure 2.1 Simple Pendulum
OBJECTIVES:
To study the use of a simple pendulum and to learn graphing techniques using a computer.
APPARATUS:
Simple pendulum, meter stick, timer and a lap top computer.
2
PROCEDURE:
Determine, experimentally, the period of a simple pendulum with a length of 98.0 cm. Allow the bob to
swing for five periods for each determination and record your data in TABLE 2.1. TABLE 2.1 is an Excel file on
the lap top computer. As you enter your raw data the computer has been programmed to calculate the period for
each of your determinations and ultimately to determine your average period for the five determinations.
Table 2.1 (Imported from EXCEL)
Your average from TABLE 2.1 is your experimental value for the pendulum.
a. EXPERIMENTAL VALUE _______________ s.
USE THE CALCULATOR AND MAKE APPROPRIATE SUBSTITUTIONS IN EQ. 2.1 TO CALCULATE THE
THEORETICAL VALUE FOR A 98.0 cm PENDULUM. SHOW ALL MATH STEPS USED TO OBTAIN
YOUR ANSWER.
b. THEORETICAL VALUE _____________ s.
2. Use your data for the theoretical and experimental values for the pendulum to determine your percent error by
substituting in EQ. 2.1
PERCENT ERROR 
THEORETICA L VALUE - EXPERIMENT A VALUE
THEORETICA L VALUE
 100
Equation 2.2
PERCENT ERROR =______________
3. From your data in TABLE 2.1, calculate the percent difference among your values for the five determinations
for the period using EQ. 2.3
PERCENT DIFFERENCE 
LARGEST VALUE - SMALLEST VALUE
 100
AVERAGE
Equation 2.3
PERCENT DIFFERENCE = __________________
3
4. Reduce the length of your pendulum by successive halves (49.00, 24.50, and 12.25 cm respectively). Let the
pendulum swing for five swings, only, at each distance and record your data in TABLE 2.2 which can be found as
an Excel file on the lap top. MAKE SURE TO INCLUDE YOUR 98.0 cm. DATA FROM TABLE 2.1 INTO
TABLE 2.2 FOR GRAPHING PURPOSES.
Table 2.2 (Imported From EXCEL)
a. USING THE SQUARE ROOT OF LENGTH DATA (Y-AXIS) AND THE PERIOD (X-AXIS) COMPUTER
GENERATE YOUR GRAPH AND DETERMINE THE SLOPE OF THE LINE. SEE YOUR COMPUTER
DATA.
SLOPE: ______________
cm
s
b. DETERMINE THE VALUE FOR “g” USING YOUR SLOPE AND EQUATION 1. REARRANGING EQ. 1
WILL GIVE:
g = 2
L
= 2  (slope)
T
YOUR SLOPE IS COMPUTED FROM YOUR DATA BY THE COMPUTER
g: ____________
c. USE EQ. 2.2 AND CALCULATE YOUR PER CENT ERROR FOR g.
PER CENT ERROR: ____________
d. FROM YOUR GRAPH, DETERMINE THE PERIOD A PENDULUM SHOULD HAVE IF ITS LENGTH IS
25.0 cm.
4
QUESTIONS:
1. What is the length, in centimeters, of a simple pendulum that has a period of one second?
2. Distinguish between percent error and percent difference.
5
Determination #
1
2
3
4
5
Average*
Time For Five Swings (s)
LENGTH OF PENDULUM(cm.) SQUARE RT. OF L*
Period*
___________
FIVE SWINGS (s)
PERIOD (T)*
6
`