Projectile Motion - Lab Book
Purpose: To investigate projectile motion and verify the equations used. To determine
how the vertical distance the ball drops is related to the horizontal distance the ball
travels when launched horizontally.
Background and Introduction: You should already be familiar with the projectile
launcher and how to measure the initial velocity of the ball. In this lab you will be setting
up your own experimental design in order to verify that the motion equations we have
been using really work. To begin, a good experiment has one variable which you control,
one variable you measure, and all other variables held constant. Once you have collected
the data a graph should be made of the variable you control and the variable which is
measured (one is independent and the other is dependent). Examine the shape of the
graph and it should show a relationship described by the equation. Straighten the graph
and the slope will be related to the variables which were held constant. A percent error
can be calculated by comparing the experimental value (slope) with the theoretical value
(using the constant values (either given or found in the Fire Away lab) in the equation to
determine what the slope should be).
Theory: The range is the horizontal distance, x, between the muzzle of the launcher and
the place where the ball lands. The range is given by x = (v0 cos ø) t, where vo is the
initial speed of the ball as it leaves the muzzle, ø is the angle of inclination above the
horizontal, and t is the time of flight.
If the ball is shot horizontally (ø = 0), then the cos ø = 1 and the range is given by
x = v0 t. The time of flight will be
t = x / v0
Eqn 1
The vertical distance, y, that the ball falls in time t is given by y = v0y t + 1/2 g t2 where
v0y = 0 thus giving y = 1/2 g t2. Substituting for time, t with eqn 1 will yield
y = (g / 2 v02) x2
Eqn 2
Procedure: To verify the case indicated in theory section you will control the x distance
and measure the y distance. Set the projectile launcher to fire horizontally off the table.
Use a vertical board as a target. You will need to measure how far the ball has fallen
when it hits the board. Use the same setting for the launcher each time to ensure a
constant velocity.
Conclusion: Your grade for this assignment will center around your conclusion. Type
your conclusion (individually) with the following formatting: underline any scientific
claims you make and bold any evidence you cite.
Notes:
Grading: This assignment is worth 40 pts. Points will be assigned for the following
areas:
Introduction (10) – Inclusion of purpose, written procedures in detail with pictures
Data (5) – table with appropriate data and formatting
Analysis (10) – inclusion and proper formatting of any sample calculations, graphs with
proper formatting, slope calculated or shown, calculation of theoretical slope, comparison
of theory to experimental
Conclusion (15) – Discuss what you did, what you found and how you know. Follow the
guidelines above concerning formatting. Think about the purpose as you write the
conclusion.