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					Physics Lab: Force/Acceleration Relationship w/ Fixed Mass                  (page 1 of 3)
(34 points)

Background:                      Materials:
In this investigation you will   PC
apply different forces to a      LabPro
object with fixed mass. A        Logger Pro
net force applied to any         smart pulley w/ table clamp
mass should produce              1-2Kg mass
acceleration in the direction    5-20g masses
of the net force. The            5 gram mass hanger
computer should simplify         several 1-2 gram masses
acceleration measurement.        string
Plotting collected data          balance to nearest gram
should help predice the
currently accepted
relationship (equation)
between force, mass and
acceleration.


Procedure:
1. Assemble the equipment as shown above. Place bricks so the cart will not slam into
   the pulley. Put 2100g of mass on the cart. To over come friction add mass to the
   hanger so the cart just begins to roll. Record your system mass to the nearest gram.
   Your system is everything that under goes acceleration. (cart/weights/hanger) Move
   20g from the cart to the hanger.

2. Plug the Photogate with a smart pulley into the DIG/SONIC1 port of the LabPro
   interface. Connect the computer to the LabPro using the interface cable.
3. Boot LoggerPro. This program will automatically recognize a modern photogate.
   (An old photogate must be manually configured.. Tap the green LabPro icon in the
   upper left corner. Tap DIG/SONIC1 and select Photogate.)
   Tap the new Photogate icon and select motion timing. Also tap the new Photogate
   icon and select Select Distance or Length. Tap the carrot and select the type of pulley
   you are using. It will probably be a 3 or 10 spoke pulley with string riding in a grove.
   Close this window.

4. Set up data collection duration.
   From the main screen select experiment/data collection and set mode to digital events
   and end data collection after 20 events. (End data collection after 6 events for a three
   spooked pullet.) Return to the main menu. Right click and delete the distance v/s time
   graph. Also delete the acceleration v/s time graph. They are not needed for this study.

5. Note that your masses must fall far enough to turn the pulley twice or the interface will
   not end data collection. Practice accelerating the cart a few times to ensure proper
   alignment.
Physics Lab: Force/Acceleration Relationship w/ Fixed Mass                   (page 2 of 3)
(34 points)

6. To measure the acceleration of this system, pull the cart back. Steady the masses so
   they are not swinging. Activate the system to start data collection. After the interface
   beeps, release the cart. Try to catch the cart before it hits the bricks.
7. You might need to adjust the axes to get a good look at the data. The slope of the
   velocity v/s time graph represents the acceleration of the masses. To fit a straight line
   to your data, drag-click and shade the area of interest. Do a linear fit. (Tap R=.)
   Record this acceleration in the data table.
8. Repeat procedure 6 and 7 above, two more times. Good data should all be close to
   each other. Redo any bad readings. Calculate and record the average.
9. Continue to repeat procedure 6 to 8 above, but each time move 20g from the cart to
   the hanger until you measure the acceleration with 100g on the hanger.


Calculations:
1. To calculate the weight force caused by the hanging mass, divide each hanging mass
   by 1000 to convert to Kg and multiply by 9.8m/sec2. The weight force will have units of
   newtons. The value of 1/(weight force) will also need to be calculated. It will have
   units of 1/N.

2. To determine the relationship between force and acceleration, make a graph of
   acceleration vs. force and a graph of acceleration vs. reciprocal force (1/force). Draw a
   best fit straight line through each graph. If you are using a graphics program: drag click
   the data of interest and select “R=” for the best linear fit. The data that produces the
   best straight line is the preferred relationship. The graph that produces a correlation
   coefficient closest to one, best describes the relationship. These graphs should be
   submitted with your report.
   Note: -- If the relationship between “a” and “F” is a directly proportional, a plot of “a”
            vs. F should be near linear. The equation F/a=m is probably true. If F is
            doubled, “a” should be doubled.
         -- If the relationship between “a” and “F” is an inversely proportional, a plot of
            “a” vs.1/F should be near linear. The equation Fa=m is probably true. If F is
            doubled, “a” is halved.
Name: ________________________ period: _______                                (page 3 of 3)

Physics Lab: Force/Acceleration Relationship w/ Fixed Mass (34 ponts)


       Total          Total                Measured acceleration                  Average
      hanging      accelerating                 (m/sec2)                        acceleration
       mass           mass
        (g)           (Kg)            Trial 1             Trial 2   Trial 3       (m/sec2)

                     (cart + 2.1Kg)


                    (same as above)


                    (same as above)


                    (same as above)


                    (same as above)

                force                           1/force              average acceleration
                 (N)                             (1/N)                     (m/sec2)




Questions: (2 point each)

1) For a fixed mass, if the net applied force is doubled, what happens to the acceleration?
   (Be specific.)


2) For a fixed mass, if the acceleration is halved, what can be said about the net applied
   force? (Be specific.)


3) For a fixed mass, what is the fancy name for the relationship between acceleration and
   the net applied force?


4) Write an equation that describes the relationship between mass, acceleration and
   force.


Summary: Your lab should contain the following:
         10 points) Data Table
         8 points) plot of acceleration vs force w/ linear regression line
         8 points) plot of acceleration vs 1/force w/ linear regression line
         8 points) answers to questions

				
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