New Jersey Center for Teaching and Learning
Progressive Science Initiative
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Inertia Lab
The goals of this lab are to:
Verify Newton’s Second Law F=ma.
Measure acceleration due to gravity, g.
Materials and Setup
Cart
Pulley
String
Masses 0.2 kg – 1.0 kg
Stop watch
Meter stick
Scale (spring or other)
A cart of mass, mcart, with an added mass, m, on a table is connected by a
string to a mass, mhang, hanging over a pulley that is fixed to the edge of the
table. The length of the string, x, is just long enough for the hanging mass to
touch the floor when the cart touches the pulley.
*The System & Measurements
F
T
a
mcart + m
mhan
g
F
T
a
mhang
g
FT = (mcart + m) a
–FT + mhang g = mhang a
Net Force on System
Total Mass of System
Acceleration of System
mhang g = (mcart + m + mhang) a
in the end also find this
vary this
find this
Guided Lab - Procedure and Examples
(For Discovery Skip to Next Section)
Procedure
Measure the time for a cart to travel the distance x, as the mass added to the cart
is changed.
Preparation:
Weigh the cart, then determine its mass mcart in kg.
Hang a small mass (10 or 20 g) on the end of the string.
Measure the distance that the cart travels: x in meters (this should be the same
as the distance from the floor to the top of the table)
For each mass: m = 0.2, 0.3, 0.5, 0.7, and 1.0 kg:
Put the mass in the cart.
Pull the cart back until the hanging mass just touches the pulley.
Let go of the cart and time how long it takes for the cart to reach the pulley. Do
this three times (enter these times, t1, t2 and t3, in columns 5, 6 and 7).
All data and calculations should be entered on the data table attached to the end
of the handout.
Data Collection and Analysis
Discovery Lab - Questions to Consider
(Guided Continues at Analysis and Application)
Given the physical quantity you are trying to find and the available
equipment:
what quantities can you measure?
how will you analyze your data? algebraically and/or graphically? what
graph or equation must you use to obtain the quantity you need to find
from those measured?
how will you ensure that your data is sufficiently accurate and thus
useable? (e.g. measurement precision, number of trials...)
what rows and columns should your data table have to collect data
and show results of calculations?
how will you do the experiment: setup equipment, perform
measurements, assign roles in your team?
if your analysis was graphical, what equation can you suggest to
predict the physical quantity you were trying to find?
what aspects of the experiment caused uncertainties in your
experimental results?
Analysis and Application Questions
What value did your group get for g?
Group 1
Group 2
Group 3
g
Why might you have different results?
Where the results differ from 9.8 m/s2, why?
Group 4
Group 5
Group 6
1
Another experiment is performed using the same apparatus as the
experiment you just completed. This time the cart with added mass
is, mcart+m = 1.8kg and the hanging mass, mhang = 0.2kg. What is
the acceleration of the cart?
2
A 20 kg mass is connected by a 100 meter cable to a 1000 kg car that
is at rest, with its brakes off, about 100 meters from the edge of the
cliff. The weight is then hung over a pulley at the edge of the cliff and
released.
What is the acceleration of the car toward the cliff?