Lab Assignment 2: Projectile Motion, physics homework help
Lab Assignment 2: Projectile Motion
Instructor’s Overview
Projectile motion is a part of our everyday experience. When you strike a baseball or softball, you are creating a projectile motion scenario. Similarly, you yourself are a projectile when you jump into a pool to cool off on a sweltering summer day. In this lab you will get some handson experience with projectile motion and apply the twodimensional kinematic equations that we have developed. You will perform experiments and compare your results to theory.
This activity is based on Lab 7 of the eScience Lab kit. Although you should read all of the content in Lab 7, we will be performing a targeted subset of the eScience experiments.
Our lab consists of two main components. These components are described in detail in the eScience manual (pages 8388). Here is a quick overview:
 In the first part of the lab, you will launch a marble off of a table or other elevated surface and measuring the horizontal distance that the marble travels. From this distance, you will calculate the launch velocity of the marble. You’ll then repeat the experiment using a different launch height and try to predict the new horizontal distance using the velocity that you derived from the first part of the experiment.
 In the second part of the lab, you will launch small foam rockets. The first part of this experiment involves measuring the flight time of the rocket and deriving launch speed. In the second part of the experiment, you will explore the dependence of range on launch angle.
Note: In the rocket experiment, perform and document steps 17. Then launch your rocket at three angles: 30 degrees, 45 degrees, and 60 degrees. Record all of your data in the tables that are provided in this document. Don’t use the tables in the eScience manual.
Take detailed notes as you perform the experiment and fill out the sections below. This document serves as your lab report. Please include detailed descriptions of your experimental methods and observations.
Experiment Tips:
Marble on a ramp
 Although you are welcome to use the water and corn starch technique outlined in the eScience lab manual, I used a slightly less messy technique. Take a towel and fold it into several layers. Place the towel in the marble landing area and smooth the surface with your hand. When the marble hits the towel, its landing is deadened and you will see a slight impression of where it landed. Measure to this impression to determine the range of the marble.
 Make sure that you place your marble at the same position on your ramp. This helps insure the repeatability of launch speed.
Rocket experiment
· I had the best results when I didn’t squeeze the launch bulb excessively. The rocket flies more consistently and travels a manageable distance from a measurement perspective.
· Before collecting data, make sure you practice you launch technique. Try to squeeze the launch bulb in a consistent manner to minimize experimental variation.
· Launch the rocket close to the ground for your range measurements.
Date:
Student: Sheena Beierman
Abstract
Introduction
Background: A projectile is an object acted on by gravity alone. A projectile is any object which, once projected, continues in motion by its own inertia and is influenced only by the downward force of gravity. In this lab, it can be assumed that projectiles are fired either vertically or horizontally.
Objective: The objective of this experiment is to predict the range of a projectile set in motion
Hypothesis: My hypothesis is that the audible noise will not be evenly spaced between each nut (part 1 of experiment), but instead will increase. With part 2 of the experiment, I believe the audible noise will be more evenly spaced due to the farther distance between nuts.
Material and Methods
The materials needed for this lab are provided below:
Experiment 1:
Ramp
Marble
Corn starch
4 sheets of black construction paper
Tape measure
Monofilament line
Fishing sinker
Paper towel*
Water*
*You must provide
Procedure:
1. Place the ramp on a table and mark the location on at which you will release the marble. This will ensure the marble achieves the same velocity with each trial.
2. Create a plumb line by launching the fishing sinker to the monofilament line.
3. Hold the string to the edge of the ramp, and mark the spot at which the weight touches the ground. Note: The plumb line helps to measure the exact distance from the edge of the ramp to the position where the marble “lands.”
4. Lay down a runway of black construct on paper.
5. Wet the marble all over with water, and drop into the cornstarch bag to coat. Roll on a paper towel to achieve a smooth, even coat of corn starch all over the marble (you do not want any chunks as it will affect the path of motion.) When the marble hits the construction paper, the force will cause some of the corn starch to come off, and leave a mark on the construction paper so you can see the point of first contact!
6. Begin the experiment by releasing the marble at the marked point on the ramp.
7. Measure the distance traveled to the first mark made on the carbon paper using the tape measure. Record this value in Table 1 on the following page.
8. Repeat steps 57 nine more times and record your data in Table 1.
9. Next, use your data to calculate the velocity of the marble for each t
Experiment 2:
4 Squeeze Rockets™
1 Squeeze Rocket™ Bulb
Protractor
Tape measure
Stopwatch
Procedure:
1. Mark the spot from which the rockets will be launched.
2. Load a Squeeze Rocket™ onto the bulb.
Note: The Squeeze Rocket™ is a trademark product name. The “rocket” itself does not use a selfpropelled mechanism. ACer a rocket is launched, gravity is the only major force which acts upon the “rocket”.
3. Using a protractor, align the rocket to an angle of 90° (vertical).
4. Squeeze the bulb (you will need to replicate the same pressure for each trial), and simultaneously start the stopwatch upon launch (alternatively, have a partner help you keep time). Measure and record the total _me the rocket is in the air. Repeat this step three or more times, and average your results. Record your results in Table 3.
tavg=______________
5. Calculate the initial velocity of the rocket (v_{initial} = v_{oy}) using the kinematics equations.
6. Record your calculation in Table 3. (Hint: you can take the initial height as zero. The vertical velocity is zero at the peak of the flight, when the time is equal to t/2.)
7. Repeat this trial two more times, and record the values in Table 3.
8. Choose four additional angles to fire the rocket from. Before launching the rocket, calculate the expected range using the vertical velocity and the angle from which the rockets will be fired. Remember that you can use zero for any initial positions, and that the acceleration due to gravity, g, is 9.8 m/s2 . Record these values in Table 3.
9. Next, align the rocket with the first angle choice and fire it with the same force you used initially. Try to record launches where the rocket travels in a parabola and does not stall or flutter at the top. Measure the distance traveled with the tape measure. Repeat this for two additional trials, recording the actual range in Table 3.
Results
Data table for marble experiment (Procedure 1):
Height = 0.610 meters 

Trial Number 
Distance (meters) 
Calculated velocity (m/s) 
1 
0.346 

2 
0.325 

3 
0.366 

4 
0.325 

5 
0.305 

6 
0.325 

7 
0.366 

8 
0.366 

9 
0.325 

10 
0.305 

Average 
0.336 

Standard Deviation 
0.0240 
Data table for marble experiment (Procedure 2):
Height = 0.814 meters 

Trial Number 
Observed Distance (meters) 
Predicted Distance (meters) 
Difference between observed and predicted distances (meters) 
1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

Average 

Standard Deviation 
Data table for rocket experiment – vertical launch
Trial Number 
Flight time (sec) 
Calculated velocity (m/s) 
1 
11.29 

2 
21.26 

3 
30.95 

4 
41.17 

5 
51.04 

6 
60.82 

7 
71.38 

8 
80.73 

9 
90.95 

10 
100.90 

Average 

Standard Deviation 
Data tables for rocket experiment – angle experiments
Angle = 30 degrees 

Trial Number 
Predicted range (meters) 
Measured range (meters) 
Difference (meters) 
1 

2 

3 

4 

5 

Average 

Standard Deviation 
Angle = 45 degrees 

Trial Number 
Predicted range (meters) 
Measured range (meters) 
Difference (meters) 
1 

2 

3 

4 

5 

Average 

Standard Deviation 
Angle = 60 degrees 

Trial Number 
Predicted range (meters) 
Measured range (meters) 
Difference (meters) 
1 

2 

3 

4 

5 

Average 

Standard Deviation 
Analysis and Discussion
Marble experiment calculations
Show your calculation of the launch velocity of the marble as a function of height and distance travelled (needed for Procedure 1 in the eScience manual):
Use your equation above to solve for the range as a function of launch velocity and height (needed for Procedure 2 in the eScience manual):
Rocket calculations
Show your calculation of the launch velocity of the rocket as a function of flight time.
Describe how you came up with your predicted ranges. What relation did you use?
Based on your experimental results, please answer the following questions:
Marble Experiment
· Suppose you altered your existing ramp so that the marbles had twice their initial velocity right before leaving the ramp. How would this change the total distance traveled and the time that the marbles were in the air?
The total distance traveled would double because they had double the horizontal speed. At the same time both marbles would spend about the same amount of time in the air since vertical motion is not affected.
· Did your prediction in Procedure 2 come close to the actual spot? Find the percent error of your predicted distance (expected) compared to the actual average distance (observed). What are some sources of error in this experiment?
% error = [ (observed value ‐ expected value)]/ expected valueX100
Air resistance could cause a source of error as well as the movement of the marble across the table. If it doesn’t roll perfectly horizontally it will cause error.
Rocket Experiment
· Of the three angles that you tested, what angle gave the greatest range? The least?
The angle that gives the greatest range is the one at 45 degrees.
· Draw a FBD for a rocket launched at an arbitrary angle (assume the rocket has just only barely left the launch tube, and neglect air resistance).
· What role does air resistance play in affecting your data?
Air resistance always plays a role in these types of experiments. Air resistance will affect the rocket’s speed as gravity pulls down. All in all, air resistance will reduce the acceleration of the rocket.
· Discuss any additional sources of error, and suggest how these errors might be reduced if you were to redesign the experiment.
Inconsistent launch speeds and movement of the rocket during the launch, since these rockets are so testy, could also be a source of error. The perfect experiment would be to use a vacuum with an automatic launcher. This would reduce the air resistance source of error as well as the movement of the rocket during launch.
· How would a kicker on a football team use his knowledge of physics to better his game? List some other examples in sports or other applications where this information would be important or useful.
To make the maximum distance for the ball to be kicked, the ideal conditions are to kick the ball at a 45 degree angle. This would make the ball move the furthest horizontally and not vertically. If I am trying to put out a fire at work with a hose, I would also want to use the same angle to ensure that enough water is hitting the fire, a type of projectile motion.
Conclusions
References
Lab 7: Projectile Motion. (2011). In Lab Manual Introductory Physics (Vol. 3.3). Sheridan, CO: Esciencelabs.com.