SOTM LAB: P1
I.
TEACHER NOTES & GUIDELINES
TITLE OF LAB: Freefall
DEVELOPERS OF LAB
Nancy Moreau, JD730@maristb.marist.edu; Philip Ousley, JD733; Mike Spear, JD743
Based on original work done by JD863 and JD566
OVERVIEW OF LAB
DESCRIPTION
Students will investigate the motion of a freely falling object using PASCO's photogate and
computer interface. A "picket fence" is used to discover the relationship between mass and the acceleration
of a freely falling body.
CURRICULUM CONSIDERATIONS
Students should have completed a discussion of constant and uniformly accelerated motion. They
should be experienced in graphing distance and time data. Interpreting the graphs presented by the software
is a major part of this activity.
Following this activity students should investigate the relationship between force and acceleration
and the factors that cause actual classroom results to differ from the mathematical predictions.
SAFETY CONSIDERATIONS
To avoid eye damage: DO NOT look at the picket fence from below.
BACKGROUND INFORMATION
A. SCIENTIFIC VIEWPOINT
Acceleration due to gravity is an important quantity in the study of the motions of objects that are
near the surface of the earth. The concept that this quantity is a constant at a given location is the focus of
this activity. Use the assumption that air resistance is negligible for this activity
B. COMMON MISCONCEPTIONS
Students often believe that more massive objects inherently fall faster, even in a vacuum!
They often confuse the ideas of velocity and acceleration and the force of gravity, thinking that acceleration
increases as velocity increases. Many believe that the moon has an earth-like atmosphere. Some students
will insist that the moon has no gravity.
OBJECTIVES
To investigate one aspect of the motion of a freely falling object (The relationship between the
mass of a freely falling object and its acceleration).
Students will gather multiple sets of data on the motion of a freely falling object.
Learners will compare the slopes of graphs of position vs time and velocity vs time.
Pupils will interpret their results and describe the relationship between mass and the acceleration
of a freely falling object.
Students will predict what a velocity vs time graph, for a freely falling object, on a different planet
should look like.
Learners will compare and contrast real data and mathematically generated data to come to an
appreciation of the differences in each group’s results.
EQUIPMENT/MATERIALS
PROVIDED BY SOTM
PASCO 500 or higher interfaces with power supplies and cables, photogates with stands, picket
fences, foam pads, a cart and track and laptops.
PROVIDED LOCALLY
Masses, tape, string and a tennis ball.
ADVANCE PREPARATION
Clean lab table surface area for each lab group expected with electrical outlets for each group.
II.
PRE-LAB
PRE-LAB EXERCISE TO ELICIT STUDENTS' PRIOR KNOWLEDGE AND
MISCONCEPTIONS
1. Discuss examples of the effects of gravity from cartoons and comic strips such as Road Runner
2. Paper falling inquiry activity. Can a sheet of paper fall as fast as a book?
DISCUSSION OF PRECONCEPTIONS
1. Discussion that could include some of the following:
a. Why do objects fall?
b. Do all falling objects fall at the same speed?
c. Do objects accelerate as they fall?
d. How would you describe the motion of a ball that is thrown upward?
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III. EXPLORATION OF SCIENTIFIC PRINCIPLE &
INTRODUCTION OF EXPERIMENTAL PROTOCOL
PROBLEM
How does changing the mass of an object affect its acceleration as it falls freely?
EXPERIMENT AND TECHNICAL OPERATION OF EQUIPMENT
1. Demonstrate the picket fence and photogate. Discuss how such an apparatus can be used to determine
velocity and acceleration.
2. Use a cart and the picket fence to demonstrate the use of the interface and the type of results that can be
expected.
3. Review the idea of slope and the meaning of slope on various motion graphs.
IV. ELABORATION OF SCIENTIFIC PRINCIPLE:
INQUIRY-BASED STUDENT INVESTIGATION
PROBLEM
What do you think would happen if two flower pots, one lighter and one much heavier, are
accidentally knocked off of a window sill on the twentieth floor of a building? Record your ideas and share
them with your group.
Design an experiment to demonstrate the validity of what your group thinks will happen.
HYPOTHESIS OR PREDICTION
Discuss with the other students in your group and predict what you believe will happen.
EXPERIMENTAL DESIGN
1. What are the variables that you will be measuring?
2. What measuring techniques will you use?
3. What tables and graphs will you need to create?
4. List safety precautions that must be observed.
5. Check with your instructor before actually setting up your experiment.
PLAN FOR DATA COLLECTION & ANALYSIS
1. What data are you going to collect?
2. How are you going to organize your data tables, graphs, etc.?
3. Check with your instructor before actually doing your experiment.
CONDUCTING THE EXPERIMENT
Students set up experiments and ask for guidance if necessary.
Checkpoint (Teacher monitors students' investigations in progress.)
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ANALYSIS OF DATA
Checkpoint (Teacher checks students' analysis.)
DISCUSSION OF RESULTS
COMPARE
1. Compare the results from at least three trials.
2. What do the slopes of the graphs represent?
3. Were your hypotheses confirmed?
PERSUADE
1. Discuss your results with another group and try to reconcile any differences in the data.
2. Decide if further trials or a different investigation is needed to clarify the relationship between mass and
acceleration of a freely falling object.
RELATE
When US astronauts were on the moon, Harrison H. Schmidt dropped a feather and a hammer, at the same
time, from the same height.
1. What would the graphs of the motions of the feather and the hammer look like?
2. How do they compare to the graphs in this lab? Be prepared to discuss any differences.
3. Is there a general statement or fact that you can state, with a high degree of confidence, about the motion
of falling objects on any planet?
V.
EVALUATION
POST-LAB SURVEY OF STUDENTS' CONCEPTIONS
Ask students to individually answer the following questions.
a. Why do objects fall?
b. Do all falling objects fall at the same speed?
c. Do objects accelerate as they fall?
d. How would you describe the motion of a ball that is thrown upward?
TRADITIONAL
Select five to ten NYS Regents type questions.
ALTERNATIVE
Given the acceleration due to gravity on Planet X is 15 m/s/s, create velocity data for the first 6
seconds of freefall (assuming no air resistance) and plot the data on a graph.
How does Planet X compare to Earth?
This material is based upon work supported by the National Science Foundation under Grant No. ESI 9618936. Any opinions,
findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the
views of the National Science Foundation.
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