Lab 3 Newtonian Dynamics
I.
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II.
Objectives
Represent Newtonian dynamics processes using words, sketches, diagrams, and
equations and to check for the consistency of one representation with others.
Test Newton’s second law by using it to predict the outcome of an experiment.
Design an experiment to complete some task.
Representing dynamics processes in multiple ways
Below you see a process represented using words, a sketch, a free-body diagram, and
Newton’s second law in component form. You are not asked to solve for anything—just
represent the process in multiple ways. Repeat the process for the problems on the next
three pages. Write your answers in the hand-in sheet.
EXAMPLE
Words: Wendy lowers the box by allowing it to slide at constant velocity down the side
of the wall. Represent the process using the box as the system.
Sketch includes:
 A sketch of the situation.
 A light circle around the system.
System
Free-body diagram includes:
 The system object is represented as a dot (a
point particle).
 Add arrows that represent the forces that objects
outside the system exert on the system object.
The forces are labeled (a symbol for the type of
force, the external object causing the force and
the system object on which the force is exerted).
 A set of coordinate axes.
y
fk wall on box
Nwall on box

Fhands on box
x
wEarth on box
The math representation includes:
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Lab 3 Newtonian Dynamics
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The application of the x and y component form
of Newton’s second law. We use abbreviated
symbols for the forces.
∑Fx = m ax
F cos + 0 – N + 0 = 0
∑Fy = m ay
F sin + fk – 0 – w = 0
Problem 3.1
Words: Two books lie on a table. Choose book 2 as the system and represent it in
multiple ways.
Sketch includes:
 A sketch of the situation.
 A light circle around the system.
1
2
Free-body diagram includes:
 The system object is represented as a dot (a
point particle).
 Add arrows that represent the forces that objects
outside the system exert on the system object.
The forces are labeled (a symbol for the type of
force, the external object causing the force and
the system object on which the force is exerted).
 A set of coordinate axes.
The math representation includes:
 The application of the x and y component form
of Newton’s second law. We use the
abbreviated symbols for the forces.
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Lab 3 Newtonian Dynamics
Problem 3.2
Words: Hank pulls a rope that passes over a pulley and down to a second pulley that lifts
a piano hanging from it. Choose the second pulley as the system and represent it in
multiple ways.
Sketch includes:
 A sketch of the situation.
 A light circle around the system.
Free-body diagram includes:
 The system object is represented as a dot (a
point particle).
 Add arrows that represent the forces that objects
outside the system exert on the system object.
The forces are labeled (a symbol for the type of
force, the external object causing the force and
the system object on which the force is exerted).
 A set of coordinate axes.
The math representation includes:
 The application of the x and y component form
of Newton’s second law. We use the
abbreviated symbols for the forces.
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Lab 3 Newtonian Dynamics
Problem 3.3
Words: Sarah pushes a crate up a ramp so that the crate moves at increasing speed. The
pushing force is exerted parallel to the ramp. There is no friction in this perfect crate.
Choose the crate as the system and represent it in multiple ways.
Sketch includes:
 A sketch of the situation.
 A light circle around the system.
Free-body diagram includes:
 The system object is represented as a dot (a
point particle).
 Add arrows that represent the forces that objects
outside the system exert on the system object.
The forces are labeled (a symbol for the type of
force, the external object causing the force and
the system object on which the force is exerted).
 A set of coordinate axes.
The math representation includes:
 The application of the x and y component form
of Newton’s second law. We use the
abbreviated symbols for the forces.
III. Coefficient of friction between dynamics cart and dynamics track
Equipment: Motion sensor, dynamics cart with friction pad, dynamics track, meter stick,
and scale to measure mass.
Task: Design an experiment to determine the magnitude of the effective kinetic friction
force exerted by the track on the dynamics cart. After your lab instructor approves the
design, perform the experiment.
Calculation: Use the results of the experiment and any other information needed to
determine the effective coefficient of kinetic friction between the track and the cart. Use
the weakest link rule to estimate the uncertainty in your value.
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Lab 3 Newtonian Dynamics
IV. Test Newton’s second law
Predict the time interval that is needed for the dynamics cart to travel 1.5m down the
inclined dynamics track. Try to choose an angle so that you have a reasonable chance of
success. Use the weakest link rule to determine the uncertainty in your prediction. After
completing your prediction, show your prediction to the lab instructor and try the
experiment in the instructor’s presence.
Was your measured value within the uncertainty of the predicted value? If not, what went
wrong (bad theory, bad measurement, bad calculation, or whatever). Be specific.
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Lab 3 Newtonian Dynamics