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Topics
Motion in one-dimension, interpretation of position vs time and velocity vs time, calculation
of average velocity and average acceleration from position vs time data.
Description
In this lab, the student investigates three different situations involving one-dimensional motion:
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Part I - Constant Velocity. A spark tape is pulled by hand through a spark timer at contant speed.
This is done for two different speeds. The student is asked to:
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compare and contrast the two spark records
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make a plot of position vs time using a spreadsheet program such as Excel and explain
why the various parts of the graph have the shapes they do
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calculate the average velocity from the linear portion of the graph
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find the equation that best fits the linear portion of each set of position-time data
and explain what each of the coefficients represent
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Part I
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Part II - Motion of an Object Accelerates and then Deaccelerates. The spark tape is attached
to a toy truck with an inertia motor. The truck is pushed to accelerate it and then released
and allowed to coast to a stop. The student is first asked to predict what the position vs
time and velocity vs time graphs will look like and then do the following:
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make plots of position vs time and velocity vs time from the data and compare the data graphs to
their predicted graphs
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determine the maximum speed of the truck from the graphs
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calculate the average acceleration and the average deacceleration of the truck
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find the equation that best fits the linear portion of each set of position-time data
and explain what each of the coefficients represent
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Part II
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Part III - Motion of a Freely Falling Object. A mass is attached to the spark tape and allowed
to fall while pulling the spark tape through the timer. Depending on the time available,
students take data for different masses. An analysis of the data similar to part II is
done.
This is often the first lab of the term so the students are often introduced to the use of a
spreadsheet program to plot and analyze data.
Sample Spark Tape Record
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Part III
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Write-ups
Sample Data
Part I - Constant Velocity. This graph shows the position vs time plots for two spark tapes
pulled through the spark timer at different constant speeds.
Part II - Speeding Up and Slowing Down. This graph shows the position vs time and the velocity vs time
plots for the motion of the toy truck.
Part III - Motion of a Freely Falling Object. The graph below shows a plot of position vs time for three mass values, 10
g, 50 g and 200 g. The equations for a least squared 2nd order polynomial fit to each data set are given to the right of
the graph.
Equipment
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Number of set-ups available: 20
Per lab station:
1 spark timer
1 level
4 hooked weights (200, 100, 50 and 20 g)
1 roll of spark paper/scotch tape
1 C-clamp
2 3-pronged clamps
2 ring stand clamps
1 long metal bar
1 alligator clip
1 1-holed paper punch
1 box with foam cushion
1 roll of scotch tape
2 meter sticks
2 meter sticks position sliders
Class Items:
lab computers with Microsoft Excel installed - number depends on availability
supplemented by student computers
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Spark Timer
Slider for Determining Position
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Lab Computer with Excel
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Toy Truck for Part II
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Small Items for Part III
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Notes
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The spark tape is coated on one side with a conducting material. The conducting side is shiny and must be facing the tips of the
electrodes inside the spark timer (i.e facing out) in order for data points to be recorded on the spark tape.
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The tips of both electrodes in the spark timer must be simultaneously touching the spark tape in order to get a
data point. The position of the tip of each electrode can be individually adjusted using a set screw located on the
front of the spark timer just above each electrode. These are adjusted each morning before the lab is run. However, the
spark timer does occasionally miss points. The student should inspect the tape for missed points before starting the
data analysis.
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The spark timer should be turned off before inserting a spark tape. If the spark timer is left on, it will leave spurious marks on the
tape which will sometimes make it difficult to measure the position of real data points. Also, it is possible to get a shock from
touching the tape while the spark timer is on.
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To minimize friction in part III, the spark time should be plumbed in all directions and the spark tape should be plumb to the slot through which it
drops. The frictional effect is minimal with masses of 200 g or more. Friction becomes significant with masses less than 100 g.
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When using masses of 100 g or more, the end of the spark tape should be reinforced with scotch tape before punching the
hole to hang the mass. Without the reinforcement, the hooked mass will tear through the tape.
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