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Activities Using the String Racer

This activity is an example how relatively inexpensive toys can be used to collect data in physics experiments. Why is it effective to use toys as a teaching tool in the physics lab? Using toys increases students' interest as they want to manipulate and play with familiar objects. Students will generally be more likely to try to "figure out" how a toy works rather than a more technical object because the toy fits into their real world.

A toy called the String Racer can be used to experimentally examine acceleration in a study of Kinematics in One Dimension. Students can collect data using stopwatches to graphically analyze acceleration. A sample lab activity follows:

Objective: To graphically describe acceleration and to experimentally determine a value for the acceleration due to gravity.

Materials: String Racer, nylon string, stop watches, meter stick, red marker, two hooks (mounted in the wall and/or on the ceiling), turn buckle (to tighten the string), rubber stopper (at end of string)

Procedure:

  1. Use the red marker to mark off the nylon string in 0.50 m for the first three meters and then in 1.0 m increments for the remaining length of the string.
  2. Position students with watches along the string.
  3. Have students record the time it takes for the String Racer to travel the different distances. Record. It is best to use several timers for each distance and take an average.

Data:

distance in meters time in seconds
0.5 m
 
1.0 m
 
1.5 m
 
2.0 m
 
2.5 m
 
3.0 m
 
4.0 m
 
5.0 m
 
6.0 m
 

  • Statistical analysis of data using the TI-83:
    1. Analysis of the position vs time graph:
      • Data can be stored in lists in the TI-83 using the stat list editor. To display the stat list editor, press STAT and select 1:Edit from the STAT EDIT menu.
      • Enter time data into list L1 and position data into L2. You can clear any existing data in either or both of these lists by using the up arrow to move the cursor onto the L1 or L2 and pressing CLEAR, ENTER.
      • Press 2nd [STAT PLOT] 1 to select 1:Plot1 from the STAT PLOTS menu. With the cursor on On, press ENTER to turn on plot 1. In the same manner, select a scatter plot. Enter L1 for Xlist: and L2 for Ylist:.
      • Press ZOOM 9 to select 9:ZoomStat from the ZOOM menu.
      • To determine the line of best fit for the data, press STAT, CALC 5:QuadReg from the STAT CALC menu.
      • QuadReg is pasted to the home screen. Press 2nd [L1] , 2nd [L2] , Press VARS, Y-VARS, 1:Function, 1:Y1, Enter Enter. The quadratic regression equation is calculated and stored in Y1.
      • Press GRAPH to display the scatter plot and the regression line.

      • The quadratic regression is in the form   y = ax2 + bx + c which corresponds to
        d = (1/2 a)t2 + vit + do.
        The coefficient a can be used to find the acceleration due to gravity. Measure the angle of the lowest point of attachment of the string relative to the horizontal. You can use a = g sinq to determine an experimental value for g.

    2. Creation of an average velocity vs time graph:
      • Press STAT and select 1:Edit from the STAT EDIT menu.
      • The TI-83 will calculate a value for the average speed for each time interval. With your cursor on L3, type L2 / L1, ENTER.
      • Press Y=. With your cursor on the equals sign for Y1, press ENTER to turn off Y1.
      • Press 2nd [STAT PLOT] 1 to select 1:Plot1 from the STAT PLOTS menu. With the cursor on Off, press ENTER to turn off plot 1.
      • Press 2nd [STAT PLOT] 2 to select 2:Plot1 from the STAT PLOTS menu. With the cursor on On, press ENTER to turn on plot 2. In the same manner, select a scatter plot. Enter L1 for Xlist: and L3 for Ylist:.
      • Press ZOOM 9 to select 9:ZoomStat from the ZOOM menu.
      • To determine the line of best fit for the data, press STAT, CALC 4:LinReg from the STAT CALC menu.
      • LinReg is pasted to the home screen. Press 2nd [L1] , 2nd [L3] , Press VARS, Y-VARS, 1:Function, 1:Y2, Enter Enter. The linear regression equation is calculated and stored in Y2.
      • Press GRAPH to display the scatter plot and the regression line.

      • The linear regression is in the form  y = ax + b which corresponds to
        v = at + vi
        The coefficient a can be used to find the acceleration due to gravity. Measure the angle of the lowest point of attachment of the string relative to the horizontal. You can use a = g sinq to determine an experimental value for g.

  • Statistical analysis of data (calculus-based method) using the TI-83:
    1. Creation of a velocity vs time graph:
      • After completing step one, select Y=. Your cursor should be to the right of the equals sign for Y2.
      • To display the MATH menu, press MATH. Select 8:nDeriv(. This is now pasted into Y2.
      • Press VARS, Y-VARS, 1:Function, ENTER, Y1, Enter. Next, press , X , X )
      • Press GRAPH to display the regression line representing the velocity vs time graph.
    2. Creation of an acceleration graph:
      • After completing the previous step, select Y=. Your cursor should be to the right of the equals sign for Y3.
      • To display the MATH menu, press MATH. Select 8:nDeriv(. This is now pasted into Y3.
      • Press VARS, Y-VARS, 2:Function, ENTER, Y2, Enter. Next, press , X , X )
      • Press GRAPH to display the regression line representing the acceleration graph.
      • Press TRACE to determine the value of the acceleration.

    Clips can be attached to the base of the String Racer. These can be used to mount a home-made, water-filled accelerometer to it. With this mounted on the String Racer, students can compare the direction of the acceleration when the String Racer slides down or is pushed up the string.

    The String Racer is no longer readily available. One can easily be made using the directions below for approximately $4.50/unit.

    Assembly Directions for String Racer

    Assembly Directions for Accelerometer

    This lab activity is based upon an activity developed as an AAPT/PTRA training activity by Jodi and Roy McCullough.