Lab Activity: Projectile Motion
Phys221
Projectile Motion
Goal
To find, in three different ways, the initial velocity v0 of the ball launched by a spring gun.
Equipment
Spring gun, ball, meter sticks, carbon paper
Procedure
Method 1: launch horizontally
1.
2.
3.
4.
5.
6.
7.
Draw a sketch of your setup.
Make sure the space is clear in front of the ball-launcher. After the initial trial to find out how far
the ball will travel, station one of your lab group members at the end of your “lane” to stop people
from passing through.
Do not cock the spring gun until just before firing it.
Keep the pendulum raised up; we won’t use the pendulum for this lab.
To load it, place the ball on the end of the launcher and press hard until the trigger engages the
spring. Note that there are three cocking positions, so choose one and use it consistently.
After one trial firing to find out approximately where the ball will land, tape a piece of carbon
paper face up on the floor and tape a piece of regular paper over it. If we don’t have carbon paper,
just tape regular paper to the floor. In this case, you will need to watch very carefully and mark
where the ball lands with a pencil.
Now take data: launch the ball about six times to measure the horizontal distance which the ball
travels. You may find it useful to hang a plumb-bob (a weight at the end of a string) from the
edge of the table in order to make accurate distance measurements.
Method 2: launch vertically
1.
Use a meter stick to measure the vertical height attained by the ball when it is launched straight
up. Again, take about six measurements.
Method 3: launch at an angle
1.
2.
3.
Prop up the front end of the ball-launcher.
Measure the angle at which the ball will be launched (your angle must be greater than 25 degrees).
Measure the distance the ball travels using the paper and carbon paper (or pencil). Take about six
measurements.
Calculations
1.
2.
3.
For each of the three ways of measuring above, find the average displacement x traveled by the
ball.
Use this displacement, other known quantities, and your kinematic equations to find the initial
velocity vi of the ball. Do this three times, one for each different method.
Compare the three results. Are they reasonably similar? Relative errors?
Typed report (1 per group)
For each setup do points 1-4:
1. Description of the experiment (include a sketch of the setup that introduces all variables used)
2. Derive an equation that allows you to determine the launch speed experimentally and clearly state
which quantities you need to measure.
3. Present your data (organized in tables if necessary)
4. Show your calculations and result for the launch speed.
Finally, …
5. Compare your three results and give your conclusion (errors, etc…)