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Physics 20: eLab Activity

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Projectile Analysis

Background:

The time that a projectile is in the air and the distance it travels is dependant a great deal on the angle of launch and the initial velocity of the projectile. Analyzing this projectile motion can be challenging because small changes in launch angle can produce equally small changes in flight time that can be difficult to record.

In this lab you will use a projectile launcher and timing pad to gather accurate flight time data for projectiles. The range and time data collected will be compared to theoretical values to determine the efficacy of projectile motion analysis equations.

The Question:

What is the flight time and range of a launched projectile?

Variables:

This experiment involves these variables: launch angle, initial velocity, flight time, range. Identify and state the manipulated, responding, and controlled variables in this investigation.

Materials:

  • projectile launcher
  • two photogate heads
  • Pasco 750 interface or USB links and 2 photogate ports
  • time of flight accessory with phone jack extender cable
  • plastic projectile launcher balls
  • tape measure
  • safety glasses
  • computer and DataStudio software

Procedure:

Step 1:

Mount your photogate heads to the projectile launcher, then connect the photogates to the interface (either the 750 interface or the photogate ports connected to USB links). The photogate mounted closest to the projectile launcher should be plugged into position 1.

Another photogate port (or the third port on the 750 interface) will be used to plug in the time of flight accessory.

Step 2:

Configure your data collection software to display digital displays of initial velocity and flight time. A table display of those values will also work. An easy way to do this is to open the pre-configured experiment "P37 Time of Flight" from the DataStudio library. If you don't have the library, you can download it:
mac files (2.0 MB)
windows files (1.4 MB)

When you have opened the Time of Flight file, a table will open (close the workbook window, it is not needed) - it will have some pre-recorded sample data already in it; either delete the data or ignore it:

Step 3:

Make sure the projectile launcher is firmly secured to the surface it's resting on. Set the launcher to fire horizontally. Note that the projectile launcher indicates launch angle at the back of the launcher:

Step 4:

Make sure you are wearing your safety glasses. Load the launcher to the shortest range setting with a plastic ball using the provided plunger. Place the time of flight pad on the floor in front of the launcher. Make sure the firing path in front of the launcher is clear. Pull on the trigger of the launcher and note where the ball lands. Adjust the time of flight pad position on the floor accordingly, and repeat loading and firing the launcher until you are sure the time of flight pad is in the correct position.

Step 5.

Reload the projectile launcher. Press "start" in the DataStudio software, then pull the trigger of the launcher to fire the ball. Observe the time of flight pad carefully and note where on the pad the ball strikes the pad. Once the ball strikes the pad, press "stop". Record the values reported for initial velocity and flight time. Repeat two more times.

Step 6.

Use the tape measure to determine how far horizontally the ball traveled. Do this by measuring from the second photogate on the projectile launcher to the horizontal distance where the ball struck the time of flight pad. Also measure how far the ball fell (height) by measuring from the floor to the height of the second photogate attached to the projectile launcher:

Record the height and range you have measured.

Step 7.

Repeat procedure steps 4 through 6 using the different range settings on the projectile launcher. Perform the following Analyzing and Interpreting steps for each of the range setting launches you perform.

Analyzing and Interpreting:

1. Use the values you recorded for flight time and initial velocity to calculate the theoretical range of the ball. Compare this theoretical value to the actual range you recorded with the tape measure. Calculate the percentage difference between the two values, and account for any significant difference.
2. Based on the height measurement you recorded in procedure step 6, calculate the theoretical flight time of the ball. Compare this theoretical value to the actual time you recorded with the computer. Calculate the percentage difference between the two values, and account for any significant difference.

Forming Conclusions:

3. What is the flight time and range of a horizontally launched projectile? What factors affect how far a horizontally launched projectile travels?

Applying and Connecting:

4.

Earlier in Unit 1 you learned how to construct velocity-time graphs. Sketch a velocity-time graph, and on it plot two lines. Considering the results of this lab:

  • the first plotted line should represent the horizontal component of the motion of the projectile.
  • the second plotted line should represent the vertical component of the motion of the projectile.

Extending:

5. Consider repeating this lab under the following circumstances:
  • Launching the projectile at different angles with zero vertical displacement. To accomplish this, you will have to raise the time-of-flight pad to the same horizontal height as the second photogate on the projectile launcher, and set the projectile launcher at an angle.
  • Launching the projectile with non-zero vertical displacement. To accomplish this, you will have to lower the time-of-flight pad to a position lower than the projectile launcher, and set the projectile launcher at an angle.
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