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PHY213 Online Lab 01

PHY213 Physics I

Lab 01: The Moving Man PURPOSE The purpose of this experiment is to explore position, velocity, and acceleration graphs, as demonstrated by a moving man. You will use an online simulation (screen shown in Figure 1) from the University of Colorado, Boulder, called PHET Simulation – Moving Man. Make sure you have checked the “Labs!” subfolder in the “Start Here!” tab to make sure you are set up properly to view these simulations!)

THEORY Absolute position is just a number in space. On a number line, it can be positive or negative. Displacement is the change in position, final minus initial. It can also be positive or negative, but it depends on direction. On our one-dimensional number line, positive displacement is to the right and negative displacement is to the left. Velocity is displacement per time, so it also has a positive or negative direction. Acceleration is the change in velocity per time. It too has a positive or negative direction, depending upon whether the velocity is increasing or decreasing over that time interval. The slope on a position vs. time graph is velocity, since it represents a change in position (rise) over a change in time (run). Likewise slope on a velocity vs. time graph is acceleration. In the reverse sense, since integration is finding the area under a function, the area under an acceleration vs. time graph is velocity, and the area under a velocity vs. time graph gives displacement.

OBJECTIVES In this experiment, you will • 1. Investigate position, velocity, and acceleration graphs. • 2. Duplicate some of these motions with the “Moving Man.”

SETUP Load the “Moving Man” simulation by either clicking on the above link, or by clicking on the red JAVA file in the lab folder in Blackboard. Immediately click on the tab. Your screen should now look like Figure 1 at right:

Figure 1 Page 1

PHY213 Online Lab 01

PART I: FAMILIARIZATION Play around with the simulation and get used to the controls. Experiment to find… ❑ At least two different ways to move the man around. ❑ How to make the man move automatically. (Hint: Try putting values into the various boxes and then hit the play !

button.)

❑ How to record and playback the man's motion. ❑ How to quickly reset the simulation to the starting conditions.

1. Try different ways to set the man’s position. First try to click (hold) and drag the man to the position of the house. 2. Click the ! button. Now, on the Position slider, move the slider to a position of about +8.0 m. In the simulation, how is this different from physically dragging the man to the house position? When the man is dragged with the mouse, not only is the position changed, but the velocity and the acceleration changes as well. When just the position slider is moved, nothing else changes besides the position of the man

3. Click the ! button again. Now input a position of “8.0” into the white box, and then hit return. This is probably the most accurate way to achieve a position in this simulation. ☺ 4. The moving man applet allows you to control the velocity at which the man walks. Play around with this control until you gain an intuition as to how the motion of the moving man relates to the velocity setting.

5. By observing what happens with the velocity setting, answer the following questions: X True ___ False If the velocity is negative, the man is walking towards the tree

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PHY213 Online Lab 01 ! ___ True X False If the velocity is positive, the man’s position is positive .! ___ True X False If the velocity is negative, the acceleration is negative. ! ___ True X False A negative velocity means the man is slowing down. ___ True X False If the velocity is zero, the moving man is at the origin. !

PART II: SCENARIOS 1. Consider this Scenario #1: A man starts at the origin, walks towards the tree slowly and steadily (constant velocity) for 6 seconds, then stands still for 6 seconds, and then turns around and walks towards the house steadily about twice as fast for 6 seconds. 2. Which of the following velocity versus time graphs conveys this type of motion? (in answering this, note that velocity is directional—i.e. a movement to the right will be positive and a movement to the left will be negative!) (indicate the correct graph F)

3. Which of the following position versus time graphs also conveys this same motion? (indicate the correct graph B)

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PHY213 Online Lab 01

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PHY213 Online Lab 01 4. Now you will try to duplicate this motion using the Moving Man. First try to duplicate the motion using the Position slider. For example, click the record/play button. Now gradually move the slider down to a position of about -8.0, hold for 6 seconds, then move it sleadily faster upward till the slider reaches +8 (the position of the house). Now click the stop/pause

button. If

you are not satisfied with your run, hit the

button and try again.

5. When you feel you have a satisfactory run, save what you see on your screen, i.e. do a “screen save.” On many computers this is achieved by holding the ALT key and hitting the “PrtScn” (or “PrintScreen”) button. Now paste your screen-save in the space below. This can done by first clicking into the space below. Now hold the CTRL key and hit “V.”

6. Now you will try to duplicate the same motion by using the Velocity Slider. Hit the button. You’ll want constant velocities for each 6-second interval. First you’ll want a velocity of -1.33 for 6 seconds—i.e. move quickly to about -1 and then count “one…two…three…etc”; then move to a velocity of “0” for the next 6 seconds; and finally move to +2.66 for the final 6 seconds.

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PHY213 Online Lab 01 Do your best, but don’t worry too much if you can’t be perfect. Again, if you are not satisfied with any particular run, hit the

button and try again.

7. When you feel you have a satisfactory run, do another “screen save” and paste into the area below:

8. Scenario #2: A position vs time graph of a moving man is depicted below. Recreate this graph for the Moving Man simulation by using any method you choose. Then use “Playback” to re-live the motion as many times as you like.

9. At which of the lettered points on the graph: a.

is the man’s motion slowest?

b.

is the man’s speed fastest?

a Xb

c

d Xe

b

c

d

Xa Page 6

f e

f

PHY213 Online Lab 01

c.

is the man turning around?

a Xb

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c

d

e

f

PHY213 Online Lab 01 10. Scenario #3 (Acceleration): The moving man simulation allows you to set him into “Accelerate” mode and control the acceleration of the man using the acceleration slider. Play around with this control until you gain an intuition as to how the motion of the moving man relates to this acceleration setting. Then answer the following true/ false questions. ! ___ True X False If the acceleration is zero, the man must be standing still. ! ! ___ True X False Negative acceleration means the man must be slowing down. ! ___ True X False Velocity and acceleration are always the same sign (both positive or both negative).! ! ___ True X False If the speed is increasing, the acceleration must be positive. ! !

11. How do you know on a velocity vs. time graph if the acceleration is positive or negative? If acceleration is negative, then the velocity will be decreasing. If the acceleration is positive, then the velocity will be increasing.

12. What happens when you have a positive velocity and a negative acceleration? When the simulation is set to a positive velocity and a negative acceleration, the acceleration stays the same but the velocity decreases.

13. What is the difference between an object with constant acceleration and an object with constant speed? Constant speed indicates that there is no change in acceleration or velocity, it is constant. Constant acceleration indicates that the speed is increasing at the same rate each second. ! !

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PHY213 Online Lab 01

PART III: MOVING PREDICTIONS 1. On the graph at right, draw an example of The Moving Man moving forward from 0 meters at a velocity of 2m/s for 4 seconds. Create a graph for both Position vs. time, and Velocity vs. time. 2. Note: To draw on this graph, click on the shapes menu above in Word. Then select the “scribble” icon. This should allow you to write on the graph image at right —using your cursor, of course.

3. Try to duplicate this motion with the Moving Man simulation. Use any method you choose to do this.

4. Draw an example of The Moving Man moving backward from zero at a velocity of -5m/s.

5. Again, try to duplicate this motion with the Moving Man simulation.

6. Click on the Clear button at the bottom. Make sure the program is paused. Type into the Position box -10, and +4 into the Velocity box. Draw what you think both graphs will look like in the picture. 7. Now, click on the play button. What happened? The man moved from left to right and the velocity and acceleration were constant.

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PHY213 Online Lab 01

8. Do a screen save (see directions for this earlier) and paste your results in the space here:

9. Click on the Clear button at the bottom. Make sure the program is paused. Type into the Position box 8 and -2 into the Velocity box. Draw what you think both graphs will look like in the picture.

10. Now, click on the play button. What happened? The man moved from right to left. The velocity and acceleration were constant.

11. Do a screen save (see directions for this earlier) and paste your results in the space here:

PHY213 Online Lab 01

QUESTIONS

1.

Complete the following sentences: a. "The slope of a linear position graph tells us the velocity of the object."! b. "The slope of a linear velocity graph tells us the acceleration of the object."! c. "For an object moving at a constant speed, we would expect to see a position graph with a straight diagonal shape and a velocity graph with a straight horizontal shape."

! 2.

"For an object moving at a constant acceleration, we would expect to see a position graph with a curve shape and a velocity graph with a diagonal shape."!

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PHY213 Online Lab 01

CONCLUSION Write a conclusion summarizing the results of this experiment. Be sure to 1. Restate the purpose, 2. State the main data values that pertain to the purpose, 3. State the % error on these main data values (if applicable), and 4. State at least three sources of error in the experiment. The main purpose of this lab was to determine the relationship between the position of an object, acceleration, and velocity. This was done by changing the different values for the “moving man” and evaluating what happened. Such as changing the velocity number and seeing how it effected acceleration. Some errors occurred in this experiment. The main error was that it was difficult to properly move the “man” accurately where he was supposed to go. If this was improved, then the result graphs might have been more accurate. Another error that occurred at first, was correctly setting the velocity and acceleration. With some problems it was difficult to slow the “man” down enough the evaluate what was happening to the velocity, acceleration, and position.

When you have filled in all of your data, answered the questions, and filled in the conclusion, you are ready to save this file and submit it. Go up to the “File” menu and “Save As” a PDF file to your computer. Use the following format for the name of the file: “LastName_FirstName_01.” Then attach this PDF file to a message to me, “John Golben Instructor.” Thank you!

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