FVCC Physics I Laboratory
Newton’s 2nd Law
February 10, 2014
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Objective
During this lab period, you will collect data on acceleration of an object and the force required to
produce this acceleration. Plotting the data will allow you to determine the mass of the object, verifying
Newton’s second law. Specifically:
1. Test fundamental statement that inertial mass as prescribed in Newton’s second law is the same
as the mass we find on a laboratory scale.
2. Use your experimental apparatus to test the problem of friction. Can you use the apparatus to
measure the kinetic coefficient of friction?
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Physics 1 Laboratory
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Newton’s 2nd Law
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Concept
Newton’s second law of motion relates an objects acceleration to the force creating that motion.
X
F~ = m~a
(1)
The equation is essentially a linear equation matching the format of a line, y = mx + b. Given a
horizontal force applied to a mass on a frictionless surface we get the simplest form of the second law.
F = ma
(2)
Using this equation, if a is plotted on the abscissa (x-axis) and F on the ordinate (y-axis), then it creates
a straight line intersecting the ordinate at the origin and having a slope equal to the mass. So, simply
by measuring the force and acceleration of an object on a low friction surface gives a way to measure
an objects inertia, as quantified by the mass.
If the mass is placed on a horizontal surface with friction, then the second law captures the friction
as in equation 3.
F = ma + µk mg
(3)
This is a straight line with an intercept µk mg. If the mass is placed on an incline plane with no friction
then the mathematical form of the motion looks like equation 4.
F = ma + mg sin θ
(4)
Here the intercept is mg sin θ. Measuring the force and acceleration directly allows us to plot the lines
and determine the mass of the object as well as other external forces like friction in equation 3 or
inclination in equation 4.
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Tools
Here is a brief description of some of the tools you can use to complete your objective. While there are
no doubt many methods to achieve the objectives, it is easier to simply use the Vernier equipment that
was made to do this lab. The experimental set-up will look something like Figure ??.
Force Vernier Dual Force sensor: This is a sensor that detects and electronically records the force.
Acceleration Vernier acceleration detector: This sensor detects and electronically records acceleration.
LabQuest Vernier data acquistion system. Plug detectors into the LabQuest and it will automatically
recognize them. Set up data collection so that data will be collect for a short time while you shake
the system and collect data.
Physics 1 Laboratory
Newton’s 2nd Law
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Logger Lite To get data off of the LabQuest and into the computer, LoggerLite can be used. This is
the free version of Vernier’s software for data collection. To manipulate and plot the data you’ll
want to export the data to a tab delimited or comma separated file. This is something that Excel
can read.
Excel It is recommended to process, sort, store and plot the data in Excel.
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What is in your Report
Here is a list of suggestions that should be in your report. It is not intended as complete list, rather it
is guidance.
Objective Statement Concisely state what you are trying to do.
Theory Explain how you will complete the objective. It is here that you will display any derived equations
that you intend to use.
Diagram of Experiment A sketch of the apparatus as it is used pointing to where critical measurements are made.
Procedure Step-by-step procedure for at least the critical steps.
Data List all the data that is taken. Tables are usually good for this. The results can also be in the
table.
Error Analysis Error estimates should be included in all the measurements.
Explanation of Data Analysis Briefly explain how the data was calculated.
Graphs
Conclusion It is important that you tell the reader what you concluded. Did you meet your objective?
Why or why not.