# 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

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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

Simple measurements & Free fall

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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).