PHY 1321 Lecture Notes - Lecture 1: Tral, Cutepdf, Fast Fourier Transform

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3 Oct 2015
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Simple measurements & Free fall
1
Simple measurements & Free fall
Introduction
The purpose of this experiment is to practice basic experimental measurements, calculation techniques and result
presentation methods (tables, graphs, etc.) that will be useful during the whole semester. Most of the subjects
covered during this experiment are presented in the following tutorials:
Measuring techniques
Experimental errors
Propagation of errors
Repeated measurements
How to present a calculation example
How to prepare a graph
How to prepare a table
These documents are available in the Tutorial section at the BbLearn physics laboratory website. Students should
read these tutorials before coming to their lab session.
Part 1 Length measurement
In this part, you will make length measurements using a meter stick, a vernier caliper and a micrometer. You will
learn how to report the uncertainty of your measurements and how to use them to perform error calculations
when calculating the density of some unknown materials.
NB. The term “cube” is used in this experiment for simplicity. The first object you will measure is actually a
parallelepiped which may have different side lengths. You will be measuring the lengths of each side separately for
your calculations.
Part 2 Time measurement
For this part, you will carry out several time measurements of the period of oscillation of a mass-spring system.
You will use these repeated measurements to calculate statistical quantities such as the average, the standard
deviation and the standard error.
Part 3 Picket fence free fall
In this last part, you will use automated data acquisition to determine the velocity of a free falling object as a
function of time (𝑣(𝑡)= 𝑣𝑜+𝑎𝑡). We say an object is in free fall when the only force acting on it is the Earth’s
gravitational force. No other forces can be acting; in particular, air resistance must be either absent or so small as
to be ignored. When the object in free fall is near the surface of the earth, the gravitational force on it is nearly
constant. As a result, an object in free fall accelerates downward at a constant rate. This acceleration is usually
represented with the symbol 𝑔 and has a value of 9.81 m/s2.
In this experiment, you will have the advantage of using a very precise timer connected to the computer and a
photogate (see Figure 1). The photogate has a beam of infrared light that travels from one of its arms to the other.
It can detect whenever this beam is blocked. You will drop a piece of clear plastic with evenly spaced black bars on
it, called a Picket Fence, through the photogate. As the Picket Fence passes through the photogate’s arms, the
computer will measure the time from the leading edge of one bar blocking the beam until the leading edge of the
next bar blocks the beam. This timing continues as all eight bars on the fence pass through the photogate. From
these measured times, the program will calculate the velocities and accelerations for this motion. Using a graph of
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Simple measurements & Free fall
2
𝑣 vs. 𝑡, you will analyse your data and use a linear regression tool to determine the value of the gravitational
acceleration 𝑔.
Figure 1 - Picket fence free falling through a photogate
Suggested reading
Students taking
Suggested reading
PHY 1121
Chapter 2
Young, H. D., Freedman, R. A., University Physics with Modern
Physics, 13th edition. Addison-Wesley (2012).
PHY 1321-1331
Chapter 2
Serway, R. A., Jewett, J. W., Physics for Scientists and Engineers
with Modern Physics, eight edition. Brooks/Cole (2010).
PHY 1124
Chapter 2
Halliday, D., Resnick, R., Walker, J., Fundamentals of Physics, 9th
edition. Wiley (2011).
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