Group member names:
Laboratory Activity 3:
Acceleration Graphs
Objectives

Explore how motions are related to acceleration-time graphs

Relate acceleration-time graphs to velocity-time graphs and position-time
graphs

Learn to use vectors to represent motion
Equipment

Computer

Ultrasonic motion sensor

USB Link

Dynamics cart

Track for cart

Fan attachment
Activity One: Speeding up
Prediction 1: Using the line tool on the drawing toolbar of Word, draw a line on
both the velocity and acceleration graphs below predicting the shape of a curve
for a cart starting at rest and moving away, speeding up at a constant rate.
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Set up the equipment: Obtain a USB Link and a motion detector as in the
previous lab. Open the experiment file called SpeedingUp.ds to display
acceleration and velocity graphs. You can find it on the class web page. Set the
detector up as in the previous lab, except make sure the switch on top is set to
the ‘cart’ instead of ‘person’ setting. Lay the track on the table and set the
motion detector on the table at the end of the track that does not have the post.
Check that the track is reasonably level by setting the cart in the middle and
seeing if it has a tendency to roll to one end. If so, level the track by adjusting
the base screw at one end. Look under the fan and check that it has two
batteries installed along with two aluminum cylinders that are taking the place of
batteries. Attach the fan to the cart and put a rubber band on to make sure it
doesn’t fall off.
Experiment: Place the cart on the track so that the fan will blow the cart away
from the motion detector. One person should hold it in position about 30 cm (1
foot) away from the detector and turn it on. Have another team member start
taking data. Let go of the cart as soon as the clicking sound is heard, careful to
not get any hands between the detector and the cart, and let the cart speed
away. Catch it just before it crashes into the other end of the track. When you
have a nice graph, copy the graph and paste it in the section below. (Note: if the
graph covers text in the document, do a right-click on the graph, chose “Format
Picture”, then click on the “Position” tab, and uncheck “Float over text.”)
-paste graph here-
Question 1: How did the result compare to your prediction? What feature of the
velocity graph shows that the cart is speeding up at a constant rate? What
feature of the acceleration graph shows that the cart is speeding up at a constant
rate? What does it mean that both the velocity and acceleration graphs are
positive (above the axis) the whole time?
Prediction 2: How will the graphs look if you start the cart at the far end of the
track and let it speed up towards the detector?
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Experiment: Set the cart on the far end with the fan blowing it towards the
detector and let it speed up toward the detector while taking data. Catch the cart
when it gets about 30 cm from the detector, so it doesn’t crash. Past your graph
below.
-paste graph here-
Question 2: How did the result compare to your prediction? What feature of the
velocity graph shows that the cart is speeding toward the detector up at a
constant rate? What feature of the acceleration graph shows that the cart is
speeding up towards the detector at a constant rate? What does it mean that
both the velocity and acceleration graphs are negative (below the axis) the whole
time?
Prediction 3: Now imagine that you return the cart to the far end of the track,
only this time with the fan blowing it away from the detector. You give it a quick
push toward the detector, with the fan blowing to slow it down, and you then
catch the cart when it has nearly slowed to a stop. Draw velocity and
acceleration graphs for this motion.
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Experiment: Set the cart on the far end with the fan blowing it away from the
detector and push it toward the detector so that it slows down while taking data.
Catch the cart when it is about stopped. Past your graph below.
-paste graph here-
Question 3a: First identify what part of the velocity and acceleration graphs
corresponds to when you pushed on the cart, and which part correspond to when
the cart was moving freely. Focus on the second part in the following questions.
How did the result compare to your prediction? What feature of the velocity
graph shows that the cart is moving toward the detector? What feature shows
that the cart is slowing down at a constant rate?
Question 3b: Do the acceleration and velocity graphs have the same sign during
the whole time? The acceleration graph has the same sign as what feature of
the velocity graph? What do the relative signs of the velocity and the
acceleration graphs tell you about the motion?
Prediction 4: In this final case, you will start with the cart about 30 cm from the
detector, with the fan blowing it towards the detector, and give it a push away
from the detector. Let the cart slow down and come back, catching it before it
hits the detector. Draw a prediction of the velocity and acceleration graphs.
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Experiment: Set the cart about 30 cm from the detector with the fan blowing the
cart towards the detector. Give the cart a quick push, being careful to not let
your hand get in front of the detector. (You may find it easier to grab the sides of
the cart or the end away from the detector.) Use the notes tool (the button with
the letter “A” right above the graph) to mark on the graph the place where you
started pushing the cart, when you let go of it, where it changed directions, and
where you caught it.
-paste graph here-
Question 4: First identify what part of the velocity and acceleration graphs
corresponds to when you pushed on the cart, and which part correspond to when
the cart was moving freely. Focus on the second part in the following questions.
What does it mean that the velocity graph changes signs? What does the point
that it is zero correspond to in the motion of the cart? Does the acceleration
graph change signs, or is it ever zero?
Summary
The following questions will help you get the main ideas out of this lab. You
should find these straightforward questions, but take the time to talk it over with
your team and write complete answers to these questions. You may find your
answers here to be the most useful part of this lab down the road.
Summary 1: In an acceleration graph, what does the vertical distance from the
axis mean? What does it mean if the line is above the axis, on the axis, or below
the axis?
Summary 2: How are velocity and acceleration graphs related? What aspect of
an acceleration graph and what aspect of a velocity graph tell us how something
is changing its motion?
Summary 3: How do you know your above statements are true? What
experimental observations and/or logical reasoning can you give to justify what
you said in summary questions 1&2?
Summary 4: Look over your graphs. How can you tell if an object is speeding up
or slowing down from velocity and acceleration graphs? If both acceleration and
velocity are positive, how is it moving? Both negative? One positive and one
negative? Explain your reasoning.
When the Lab Activity is completed, save this Word document, then email it
to:
dennis.garvey@wku.edu
Also CC the email to all group members (to refer to when writing up the
Summary Questions)