Physics 12 Lab #2
Measuring Speed and Acceleration
Theory
Speed = Distance / Time
Acceleration = Change in Speed / Time
These formulae should actually be written in vector form. We will do this later...
Procedure
You need to follow the sections in order this time. You will have to share apparatus. Be sure to stick to one sparker timer or your calibration won't be correct.
Part #1 Calibrating the Sparker Timer
The sparker timer gives off sparks that mark the ticker tape with black dots. These dots are given off at an approximately constant rate.
- Cut a piece of ticker tape of about 1.2 m length. Run this through the sparker at a fairly constant rate. Use a stopwatch to get an accurate timing of how long you are running the tape through the sparker. (It should take a couple of seconds to go the length of the tape.) The idea is to get the marks separated well enough that you can distinguish between them. However, you also want the right total number of marks: too few and you aren't getting an accurate calibration; too many and you are spending too much time counting.
- Count how many marks there are on the "run through" part of the tape. (Ignore the super cluster of marks at the beginning and end of the tape.) By dividing the time by the number of marks counted you get a calibration of the amount of time per spark for your sparker timer. If I count the number of spark intervals on a length of tape and mulitply this by the calibration factor above I can find the time elapsed from the first spark until the last. (Time = Number spark intervals x Amount of time per spark)
Part #2 Measuring Speed
If you think you did a pretty good job of getting at least a significant region of your tape with constant speed in part 1 you can use the same tape for this part.
- Find the region of the ticker tape over which the speed appears to be constant. Divide it into two halves and count the number of intervals (number of marks minus one... why?) and measure the distance for each half. Calculate the time elapsed for each half. (Remember reading errors.)
- Using the time and distance measurements above calculate the speed for each half of the tape and see if they lie within each others errors..
Part #3 Measuring Distance vs. Time for Constant Acceleration Due to Gravity
- Repeat the exercise from part 2 but use a mass attached to the ticker tape. Drop the mass from rest at the lab bench while the sparker runs. Look at the tape. How do the marks appear different from those in part 2?
- Measure the distance of the marks after each ten intervals and fill in a table of data labelled distance and time. The distance should be the overall distance from the starting point (the cluster of dots at the beginning). The time will be ten times the calibration factor for the first measurement, twenty times the calibration factor for the second measurement, etc.
- Graph distance vs. time for your data. Ignore errors.
Part #4 Measuring the Acceleration Due to Gravity
Use the data from part 3.
- Find the average speed from the tenth to the twentieth marks using the method of part 2. Do the same for ten intervals of the marks about ten marks before the end of the tape. Find the difference in speed between these two results. (For full marks do the error analysis for this.)
- The time difference between these two speeds is found by counting the number of intervals between the first marks of each segment and multiplying by the calibration factor.
- Use the formula in the theory section to find the acceleration. The accepted value is 9.8 m/s2 for the acceleration due to gravity, ignoring friction.