Lab
– Data Sheet
Determining the spring constant of the rubber band
Stretch (meters) Force (newtons)
1. Record the slope and the y -intercept from your calculator slope ___ typical value 61.6 m/N _____ y-intercept ___ typical value 0.121 N ____
2. What does the y -intercept represent?
The amount of force required to produce zero stretch.
3. What does the slope represent?
The slope represents the spring constant, the ratio of stretch to force.
Prepare the car launcher.
Initial length of the rubber band when attached to the launcher ____________
Length of the rubber band when launcher is set to second position (2 clicks)
____________
Mass of car with flag and clay Typical value 0.041 kg
Car Launchers: Lab Teacher Data Key
© 2004 The University of Texas at Austin and the GE Foundation
Page 1 of 3

Analyze the data
Explain what is being recorded in each region of the graph from the calculator.
A. Car out of range
B. Useful data, car is approaching CBR
C. Car has passed CBR
D. Car out of range
LinReg y = ax + b a = _____ b = _____
Velocity of the car typical value –2.2 m/s
Car Launchers: Lab Teacher Data Key
© 2004 The University of Texas at Austin and the GE Foundation
Page 2 of 3

Calculate input and Output Work
Work done in stretching the rubber band.
1. Differential equation for work in terms of distance and the spring constant dW
 kx dx
2. Equation for work written as a definite integral W
  kxdx
3. Work done in stretching the rubber band Typical value, 0.21 J
Kinetic energy of the car.
Velocity of car after launch (slope from linear regression) Typical value –2.2 m/s
Kinetic energy of car after launch Typical value 0.19 J
Comparing Input and Output Work
Percent of input work lost when car is launched Typical value 9.5 %
Car Launchers: Lab Teacher Data Key
© 2004 The University of Texas at Austin and the GE Foundation
Page 3 of 3