Friday 13 January 2012
Class meeting
Topics
3
1D motion
Textbook sections 2.1-2.7
Ponderables
Mini-labs (deliv.) Accelerated motion, x from t and t from x (notebook)
Lab
Demonstrations Acceleration down incline: ramp with flashing lights
Mini-lectures 1-D kinematics
Quiz
Other
Nickel density
Attitude survey
PHYS 116 SCALE-UP

Group/seat assignments
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Attitude survey (20 min): https://www.surveymonkey.com/s/BQ5DNRC
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Mini-lecture on 1-D kinematics with video demonstration (10 min): accelerated motion down an incline (ramp with flashing lights
<http://www.physics.unc.edu/demos/detail.php?demonum=1C20.40>)

Assignment preview: Moving Man (10 min): Introduce PhET simulation
< http://phet.colorado.edu/sims/moving-man/moving-man_en.jnlp> (assignment to be done outside of class)
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Mini-lab : Accelerated motion (60 min) o Equipment: 1 for each group of: dynamics tracks and carts, meter sticks, 1- and 2-cm wooden blocks/spacers, stopwatches. Metronome: http://www.metronomeonline.com/ o x from t o t from x
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Quiz (20 min): nickel density’ o Equipment: vernier calipers, digital balances (as many as possible)
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Friday 13 January 2012 PHYS 116 SCALE-UP
This mini-lab explores the concept of acceleration and its relationship to position, speed, and time. It consists of “explorations” and “applications.” The deliverable for this mini-lab will be the answers to a set of questions in the applications, to be recorded in your lab notebook.
Prelab
A ball accelerates from rest down an inclined plane. Its position after 2 seconds is marked on the drawing below.
Determine the positions of the ball after times of 1, 3, and 4 seconds since the start of its motion. If the velocity of the ball was 5 m/s after 2 seconds, what is its velocity after 3 seconds?
Briefly explain the rationale for your answers.
Explorations
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Position from Time and Quadratic Functionality. Level the track (the diagram refers to a glider and air track – your equipment may instead be a rolling cart and a plain track), then incline it by placing a spacer under one end. Place the glider/cart at the high end of the track and note its position. One person, the starter, can hold it there, while two others, the observers, sit close to the track at two positions further down. Select a time-keeping device – each observer should have one. (If you want to use a metronome, you can find one at http://www.metronomeonline.com/ ) Coincident with a given time mark, the starter releases the glider or cart. At a suitable next mark, the first observer notes the position of the glider/cart as it passes. The second observer does the same at a second mark. Record positions and time marks and repeat the procedure a few times to get an estimate of your uncertainty.
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Friday 13 January 2012 PHYS 116 SCALE-UP
For the following 4 exercises, you should make notes (and draw graphs!) in your lab notebook during class.
• Let x be the distance traveled in a certain time t. Graph the your values of x vs. t. Is x a linear function of t?
• Graph your values of x vs. t 2 (this is accomplished by squaring all the time values, and plotting the according distances). Is x a quadratic function of t? Include (x,t)=(0,0) on each graph.
• Use your data to find the acceleration.
• Repeat for a different incline (i.e., slope) and compare the accelerations. Make an
"educated guess" as to how the acceleration depends on the slope. Do the data support your guess? Can you find a relation among your measured value of the acceleration on the incline, the constant g=9.8 m/s 2 , and the slope of the incline?
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Time from Position. Again holding the glider/cart at rest and letting it go, use your timing device to make the following three determinations:
• Determine how long it takes the cart to go a distance d (about 0.75 meter).
• Determine how long it takes to go 2d.
• Did it take twice as long? How is t related to x?
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Moving Man. (to be done outside of class) – Use the Moving Man simulation to experiment with concepts of position, velocity, and acceleration. The simulation can be found at: http://phet.colorado.edu/sims/moving-man/moving-man_en.jnlp
Click on the “Charts” tab and remove the brick walls on the ends. Perform the following exercises:
1. Set the position to -10 meters, the velocity to 0, and the acceleration to +0.2 m/s 2 . Start the simulation and observe the linear velocity plot and the quadratic position plot.
2. Use the Clear button to reset the simulation and set the position to -6 meters, the velocity to
+5 m/s, and the acceleration to -1 m/s 2 . Start the simulation and observe the velocity and position plots. Note that although the plots look qualitatively different from those for exercise 1, they are still linear and quadratic, respectively. Use the Playback radio button to repeat the exercise with both the velocity and acceleration vectors turned on. Note the direction of the
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Friday 13 January 2012 PHYS 116 SCALE-UP velocity and acceleration vectors throughout the simulation. Move the speed slider to “slow” to see the results more clearly.
3. Explore the operation of the simulation to by a) setting initial conditions and running the simulation as in Exercises 2 and 3, b) dragging the man back and forth, and c) using the blue, red, and green sliders. Observe how the position, velocity and acceleration graphs are related to the man’s motion. Note specifically that each of the position values, velocity values, and acceleration values can be either positive or negative at any particular time.
Deliverable: In addition to the record of your observations from the Explorations (including the
“Moving Man”), you are to complete the Applications below in your lab notebook.
Applications
1. You drop stones down vertical mineshafts. For mineshaft A you hear the stone hit the bottom after 3 beats of your pulse. For mineshaft B you hear the stone hit after 5 beats of your pulse. How many times deeper is mineshaft B than mineshaft A?
2. Find the acceleration for both sets of data plotted below.
3. For accelerated motion, if the initial velocity is v
0

0 , then x(t)

1
2
at 2 . Invert this equation to write t as a function of x, i.e., t(x).
4. For accelerated motion, if the initial velocity is v
0

0 , then
 
1 x(t) v t at
2
2 . Invert this equation to write t as a function of x, i.e., t(x).
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Friday 13 January 2012 PHYS 116 SCALE-UP
5. An object starts at O from rest at t=0 with a constant acceleration a. At t=2, its position is at
A. If it continues with the same constant acceleration to position B, what time does it reach B?
6. An inclined plane makes a fixed angle

with the horizontal. The length of the inclined plane is 2 meters. In an experiment, an object starting from rest at the top of the plane takes 1 sec to reach the bottom. In a second experiment, the same object is given a slight push while letting it go at the top of the plane. This time the object takes 0.5 sec to reach the bottom. What is the initial speed of the object in the second experiment?
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Friday 13 January 2012 PHYS 116 SCALE-UP
What is the density of a nickel? Use vernier calipers and a digital balance to find the density of a typical nickel coin as precisely and accurately as possible. Report your intermediate and final results here:
Mass = _______ ± ______ g
Diameter = ________ ± ______ cm
Thickness = _______ ± ______ cm
Volume = _________ ± ______ (give unit)
Density = __________± ______ (give unit)
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