Lab #2
Non-Uniform Motion
Purpose
•  Analyze how the distance, velocity and
acceleration of a glider on an air-track
vary with time.
•  Understanding the difference between
instantaneous and average velocity
Air Track Procedure
•  Turn on air
•  Suspend ball bearing from pulley
•  Use a meter stick (DO NOT TOUCH THE
GLIDER!) to steady the glider such that the
ball bearing hangs just below the the pulley
•  Turn on spark timer
•  Release glider and press and hold the run
button until just before the glider reverses
direction (should have 30-60 spark points)
Analysis 1: Measure position as
function of time
•  Choose origin (not the first point!), circle and
number each point starting with the origin as
the “zero” point.
•  Constant time interval between points is 1/20
of a second.
•  Measure distance from origin to each spark
point and record in template spreadsheet.
•  Also record errors in spreadsheet. Error in
distance is from measurement error (i.e., ½
smallest unit of meter stick). Assume error in
time is negligible.
Analysis 2: Calculate Instantaneous
Average velocity
Velocity
The instantaneous velocity v at time t is the
limiting value of the average velocity, as the
time interval Δt tends toward zero.
Using a small time interval Δt, we can approximate instantaneous
velocity with average velocity calculated in the middle of the interval.
HINT: this calculation can be done in the spreadsheet.
Example for
instantaneous
velocity at
point 5.
Analysis 2: Calculate Instantaneous
Velocity Continued …
•  Derive an expression for the error in
instantaneous velocity, show why the error
is constant for all v, and calculate a value
of the error and input in the spreadsheet.
Analysis 3: Calculate average
velocity
•  Do so for the entire trip use:
•  Could you use this value to find the instantaneous
velocity of the glider at the middle of the trip?
Analysis 4: Plots
•  The template will draw two plots for you:
- distance vs. time
- instantaneous velocity vs. time
•  Choose the chart type which draws a
smooth line through your data points, and
print off the plots.
Analysis 5: Calculate Instantaneous
velocity using tangent Line method
•  Draw a tangent line at a data point on your
distance vs. time plot and calculate instantaneous
velocity (slope) and its error.
•  Compare to your instantaneous velocity data
value at that time t. Is it within error? (HINT:
compare the extent of the error bars)
Analysis 6: Instantaneous
acceleration analysis
•  Without calculating instantaneous acceleration, on
your instantaneous velocity vs. time plot:
- label 3 regions each corresponding
to a different type of motion (HINT: think
what forces are acting.)
- for each region state the behavior of
velocity and acceleration (HINT: increasing,
decreasing, constant or zero).
To include in report:
•  Data table of all relevant data, including sample
calculations, errors etc.
•  Calculation of average velocity for trip.
•  Explanation of how instantaneous velocity was
calculated, derivation of error, and calculated value.
•  Plots of d vs. t and v vs. t.
•  Tangent line method analysis (i.e., drawing and
calculation of slope and error, comparison of slope
with instantaneous velocity data).
•  Instantaneous acceleration analysis (i.e., labeling
regions, force analysis and v and a behavior on v vs. t
plot)