Projectile motion experiment is used by most schools for their first Physics practical assessment task. This is because most Projectile Motion practical investigation is relatively easy to design and conduct by students.
A typical Projectile Motion practical assessment task used by schools is outlined below.
Task titleTask 1 of 4 OpenEnded Investigation Report on Projectile Motion from Module 5 Advanced Mechanics. Task weighting20% of Overall school assessment Description of Assessment Task

In this sample practical assessment task, we are required to investigate the relationship between the range s_x and the launch velocity of a projectile released from an elevated position.
Let’s apply the scientific method to design and conduct a practical investigation for the assessment task outlined above.
The simplest type of projectile motion is a ball being projected horizontally from an elevated position.
In this situation, the range of a projectile is dependent on the time of flight and the horizontal velocity. Hence this experiment is based on the equation s_x=u_xt .
To express the time of flight t in terms of the acceleration due to gravity, we analyse the vertical motion of the projectile
s_y=u_yt+\frac{1}{2}at^2
h=0+\frac{1}{2}(g)t^2
t^2=\frac{2h}{g}
t=\sqrt{\frac{2h}{g}}
Hence the range of a projectile can be expressed in terms of the horizontal velocity and the other control variables such as y and g by substituting t=\sqrt{\frac{2h}{g}} expression into s_x=u_xt :
s_x=u_xt
s_x = u_x \times (\sqrt{\frac{2h}{g}})
\therefore s_x = (\sqrt{\frac{2h}{g}}) u_x
Before designing your investigation, all the variables need to be identified.
Keeping the control variables constant allows the experiment to be more valid.
To learn more about how to improve the validity of your experiment, read the Matrix blog on ‘Validity, Reliability and Accuracy of Experiments‘
To determine the relationship between the range of a projectile \Delta x and its horizontal launch velocity u_x and use the results to calculate the acceleration due to gravity g .
The results are given in the table below. Using the times taken for the ball to travel 1 metre. Data collected from the experiment is highlighted in blue.
Vertical height on ramp \Delta h \ (m)  Time to travel 1 \ m \ (s)  Range \Delta x \ (m) 
0.6  0.30  1.37 
0.5  0.31  1.26 
0.4  0.37  1.14 
0.3  0.40  0.98 
0.2  0.53  0.81 
Calculate the horizontal velocity of the ball as it leaves the table and hence complete the table.
Vertical height on ramp \Delta h \ (m)  Time to travel 1 \ m \ (s)  Launch velocity u_x \ (ms^{1})  Range \Delta x \ (m) 
0.6  0.30  u_x = \frac {s_x}{ t} u_x= \frac{1}{0.30} = 3.33  1.37 
0.5  0.31  u_x= \frac{1}{0.31} = 3.23  1.26 
0.4  0.37  u_x= \frac{1}{0.37} = 2.70  1.14 
0.3  0.40  u_x= \frac{1}{0.40} = 2.50  0.98 
0.2  0.53  u_x= \frac{1}{0.53} = 1.89  0.81 
Plot the range of the ball \Delta x against the launch velocity u_x and draw in the line of best fit.
Determine the relationship between the launch velocity u_x and the range of the ball \Delta x and hence discuss its significance
Use the gradient to find the acceleration due to gravity
Action  Detail 
Step 1: Find the gradient of the line of best fit. 

Step 2: Identify the variables 

Step 3: Rewrite \Delta x = (t) u_x in the form y = (k)x to determine the relationship between the dependent, independent and control variables.  \Delta x = u_x t \Delta x = (t) u_x \Delta x = (\sqrt{\frac{2H}{g}}) u_x 
Step 4: Write the gradient in terms of control variables.  Since \Delta x is directly proportional to u_x , the gradient equals to \sqrt{\frac{2H}{g}} 
Step 5: Find the unknown in the control variable.  Using the launch height y = 0.7 m and the gradient, determine the acceleration due to gravity g. gradient = \sqrt{\frac{2H}{g}} g= {\frac{2H}{(gradient)^2}} g= {\frac{2 \times 0.7}{(0.4)^2}} g= 8.75 ms^{2} The acceleration due to gravity is 8.75 ms^{2} downwards. 
Let’s investigate the errors, reliability and accuracy of this experiment.
Question  Answer 
How would you determine if the results are reliable? 

Suggest a method of improving the reliability of your results. 

What are some potential errors in this experiment? How can these errors be reduced?  The main errors experienced in this experiment are:

If a foam ball or PingPong ball was used instead of the metal ball, what would happen to the range and the value of g obtained? 

Would the use of the pingpong ball affect accuracy, reliability and/or validity? Justify your answer. 

Get free access to syllabus specific Physics Practicals written by expert HSC teachers. Join 10000+ students who are getting ahead with Learnable. Try for free now.
Learnable Education and www.learnable.education, 2019. Unauthorised use and/or duplications of this material without express and written permission from this site's author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Learnable Education and www.learnable.education with appropriate and specific direction to the original content.