2. The dots at the very top of the tape may be too close together to be useful. Choose one of the first dots which is clearly separate from nearby dots, circle it, and label it with the number 1. Proceed down the tape, circling and numbering dots until you reach dots which appear to have been made after the falling object hit the ground. As you go down the strip, look at the spacing between the dots, and try to identify any problems such as missing dots, extraneous marks which might be mistaken for dots, or dots which are not in a straight line. If in doubt, ask the instructor or lab assistant.

3. Lay a meter stick edgewise along the tape, and record the position yn of each dot to the nearest tenth of a centimeter (see the data table). The position of dot 1 is arbitrary, but you should make it close to zero. Do not lift the meter stick between readings, just proceed along the meter stick. Fill in the time column as shown in the table. We are (arbitrarily) choosing the point where time starts (i.e. t = 0) as the dot immediately before dot 1. If there is a missing dot, you can still get good results if you number the empty region on your tape, and leave a blank space for the missing dot in your table (see data table). If you don't account for a missing dot, this mistake will eventually show up as a small step in your graphs.

4. Use y₃ and y₁ to calculate the average velocity v₂ for an interval which includes dot 2. A subtle detail of this experiment is that we are going associate this average velocity with dot 2. You will eventually find out that v₂ is the same as the instantaneous velocity at dot 2.

Example (see table) : v₂ = (y₃ - y₁)/(t₃ - t₁) = (8.1 cm - 1.0 cm)/(2/30 s)

Note that we are using a time interval of 2*(1/30) and that division by 2/30 is the same as multiplication by 15. Proceed down the table calculating the average velocity for each interval. Note that you cannot calculate v₁, the last average velocity, and possibly some other velocities if you have any missing dots.

5. Make a graph of v_n (vertical axis) versus t_n (horizontal axis). Pick scales on your axes which will make your graph cover as much of the page as possible. Circle your points as you plot them. Your points should be on a straight line (or nearly so). If this is the case, you are going to assume that there is a fundamental law of nature that dictates that the points really should be on a straight line, but that imperfections in the experiment have caused some minor deviations from this law. How large a deviation can still be considered minor is a matter of judgment. Use a ruler to draw one straight line which is close to all your data points. One rule of thumb is to position the line such that there are just as many points above the line as are below it. A straight line is a very strong indication of a constant acceleration. We can't really say that we have proved that the acceleration is constant, because we are using average velocities in this experiment. If your graph levels off at some point, there may have been some friction present.

6. Assuming you have a straight line, the slope of your line is the acceleration of the falling object. Calculate this slope from two points on the line that are very far apart. These two points need/should not be data points.

7. The free fall acceleration in Emporia is expected to be g=980.0 cm/s². Calculate the percentage difference between your result and this expected value.

8. Make a graph of yn (vertical axis) versus tn (horizontal axis). You will notice that the points do not lie on a straight line, instead they are on a curve, part of a parabola to be precise. Connect the points with a smooth curve.

9. Important note: Keep this lab handy! You will need the data from it in a couple of weeks.