Forces, Acceleration, & Springs
Lab 4
Part 1 – Verifying Newton’s 2nd Law
Using the apparatus below, you will verify
Newton’s 2nd Law by applying a force to our
iOLab device and using the accelerometer and
force censor to measure both the acceleration
and the magnitude of the applied force.
1. As always, first Cali
ate both the accelerometer
and the force sensor.
2. Choose the Accelerometer Sensor and select
Ay.
3. Select the Force Sensor.
4. Click Record, then push your device wheel side
up 4-6 times across a flat surface, each with
increasing strength. Stop recording.
example https:
www.youtube.com/watch?v=OgpY_iiNanI
https:
www.youtube.com/watch?v=OgpY_iiNanI
5. Your graphs should look like the below. Zoom in around one of the peaks.
Include a screen grab of your results in your report.
6. For each of your 4-6 peaks, write down the peak acceleration found by
placing the crosshair near the highest point
(ignore small wiggles in the graph)...
6 continued… as well as the peak force...
6 continued… and place all of this information into a table. Include a screen grab of one of your
zoomed in peaks in your lab report.
7. Using a spreadsheet program of your choosing (Microsoft Excel, Google Sheets, etc.), create
a graph of Force (y-axis) versus acceleration (x-axis). Fit a linear line to your data and retrieve
the equation for the line of best fit. Because,
then the slope of your graph should give you
the mass of the iOLab device, i.e.
Likely
close to
zero.
Write down the slope from your best fit line as your experimental mass measurement. Include
this value, your table, and graph in your report (always label your axes and include units).
Applied
Bonus: Click the Parametric plot mode on the top of the page.
Make sure Force is on the y-axis
and Acceleration is on the x-axis,
otherwise use Swap Axis.
Bonus continued: Highlight just one of your peaks in the small
graph below the main graph. This will add data to your Force
versus Acceleration graph.
Bonus continued: Estimate the slope of this line to the best of your ability using
the markings on the grid. Mark this as your experimental mass measurement #2.
Demonstration Video
https:
www.youtube.com/watch?v=ELLk7WrYuHg
8. Save your data if desired (you shouldn’t need to refer back to this once you’ve measured
your experimental mass. Reset your experiment.
9. Now attach the hook to your iOlab. We will now measure the actual mass of the device.
We will do this by picking the mass up and holding it steady, then measuring the applied
force on the object as it balances out gravity.
m
10. As always, first Cali
ate both the
accelerometer and the force sensor.
11. Choose the Accelerometer Sensor
and select Ay.
12. Select the Force Sensor.
13. Click Record, then pick up the
device, hold it for a second or two, then
set it back down and stop recording.
14. Zoom in on the constant non-zero
applied force after you have picked up
the mass and before you set it down.
15. After zooming in, highlight a section
of the graph. Your graphs should now
look like...
...this.
16. Write down the average acceleration As your object is at rest, your device is
directly measuring the acceleration due to
gravity and not the actual acceleration.
17. Write down the average force.
18. Now calculate the actual mass measurement of the device by...
19. Calculate the percent difference between your actual mass and your experimental
mass,
Include this in your report. By showing that your experimental mass (the slope of the force
versus acceleration graph) is equal to the actual mass you are verifying Newton’s 2nd Law,
in that the acceleration the mass experiences is directly proportional to the force on the
object.
20. Compare your measured masses and your percent e
or with your lab partners and
include the range of values found in your report.
Bonus continued: Repeat step 19 using your experimental mass #2. Which value was
closer to the actual value? Explain.
Include this value in your report.
QUESTIONS
21. Why should the slope of the Force versus Acceleration graph tell us the mass?
Explain and show any relevant equations.
22. Why do we use 4-6 attempts, then use the slope of the best-fit line, to measure
the mass, rather than take just one push and calculate the mass explicitly? What is
the benefit to taking multiple trials and combining the results?
Part 2 – Measuring the spring constant of your spring.
We will calculate the spring constant of the
spring by measuring the applied force from
stretching the spring while attached to the
mass, as well as the displacement.
Spring constant
Displacement
from Equili
ium
1. First Cali
ate both the accelerometer and the force sensor.
2. Select the Force Sensor. Select the Wheel Sensor, and highlight only the
position setting.
3. Select the Parametric plot mode. Make sure that Force is on the y-axis
and Position is on the x-axis (otherwise click Swap axis).
4. Click Record. Hold the loop of the spring firmly in one hand, and do your best not to move
from that position. With your other hand, stretch the spring by pulling the iOLab device back
and forth at a slow-to-moderate speed (wheels down), increasing the total displacement each
time. After a total of 4-6 stretches stop recording.
5. Highlight a portion of the graph on the bottom after you began stretching and relaxing the
spring, but before you stopped applying force to the spring. This should populate the graph
as below.
6. This should reveal a mostly linear graph (the outliers are likely data between stretches and
do not apply). To the best of your ability calculate the slope of this line using the positions on
the grid. Mark this as your experimental spring constant k. Include this and a screen grab
of your graph in your lab report.
QUESTIONS
8. What are the units of the spring constant k that you measured?
9. Why is the slope of the Force versus Position graph negative?
10. Think of one other way we might be able to measure the spring constant.
7. Compare your measured k values with your lab partners and include the range of
values found in your report.
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