AP Physics Lab 1x03: Estimating Gravity
¾ with a Falling Object
¾ with a “Picket Fence”
¾ “By The Book”
Background
As an object falls freely, it accelerates due to the applied net force. If air resistance is neglected, and the
speed of the object is measured over several short, consecutive intervals as it falls, the differences in the
speed of the object can be used to determine the acceleration due to gravity.
Objectives
• to use the relationship of slope and area under a curve to analyze graphs
• to estimate Earth’s gravity
Materials
• SW500 Interface
• Photogate (or laser and Laser Switch)
• Picket Fence
• Meter stick
• Small Spheres
• Stopwatch
Procedure A – Gravity “By The Book”
• Using the page provided from the CRC Handbook of Chemistry and Physics and the USGS Topo
map for this area, determine gravity at table height for this Lab. Show all work in your Lab
Journal.
Procedure B – Gravity via a Falling Object
1. Create a method for consistently holding the sphere a predetermined distance from the floor.
Prepare a minimum of three distances. Record details on your set-up in your journal.
2. Create a table in your Lab Journal to record sphere type, drop height, and time of fall for the
sphere. (Leave room for a 4th column…)
3. Time multiple drops. For each height, use a minimum of ten drops per sphere type for at least
three sphere types.
Procedure C – Gravity via a “Picket Fence”
1. Connect the SW500 interface to the computer, turn on the interface, turn on the computer.
2. Connect the photogate (or Laser Switch)
3. Position the photogate (or Laser and Laser Switch) so that
o the beam is horizontal and
o positioned so that the Picket Fence can freely fall through the beam and be caught (or land)
without damaging any equipment or your hands.
4. Start Data Studio
5. Scroll down the sensor list and select Photogate & Picket Fence
6. Create a dual graph of d vs t and v vs t (for now…).
7. Create a table of accelerations
8. Click the Stats Button (Σ) and select Max, Min, & Mean
AP_L_1x03_EstimatingGravity
9. Resize both data windows so both can be seen.
10. Collect data from multiple drops. (Note: since the photogate only operates when an object is
passing through it, manual start and stop of runs is appropriate in this case.)
11. Save your data for later analysis
12. Look ahead through the Analysis section. Create and print all necessary graphs and tables.
(Note: by my count, you will need a minimum of 4 graphs and a table.)
Analysis (Attach typed responses)
From Part B…
1. Using the formula for distance covered by a freely falling object, calculate the value of gravity
for each trial; record in that 4th column. Show one sample calculation.
2. Why were multiple heights required?
3. Why were multiple spheres required?
4. Calculate the average value for gravity from this method. Cite answer on Analysis Sheet; show
work in Lab Journal.
From Part C…
5. From the statistical and/or quadratic fit information provided on the d vs t graphs, estimate
gravity for Earth. Explain what characteristic of the graph you used and why.
6. From the statistical and/or linear fit information provided on the v vs t graphs, estimate gravity
for Earth. Explain what characteristic of the graph you used and why.
7. From the statistical information in the acceleration table, estimate gravity for Earth. Explain
what characteristic of the table you used and why.
General…
8. Provide a Table of Results showing the final value for gravity from each method. Compare your
estimates from this experiment to the “book” value. (Too high? Why? Too low? Why? R%E?...)
9. Discuss (and show the mathematical equivalence of) the data plotted on the d vs t graph and
the area under the v vs t graph.
10. Given the fact that the computer system is able to measure time to the nearest 1/10,000 s and
is able to exactly replicate the instructions that it is given for every trial, one would assume that
the data would be exactly the same for every trial. Was it? If not, where/what were the errors
and how would you correct for them?
11. Consider a v vs t graph of multiple trials. Why do the graphs all have the same slope?
12. Consider a v vs t graph of multiple trials. Why do they all have different X-intercepts?
13. Attach all print outs in the order referenced during analysis.
AP_L_1x03_EstimatingGravity