Background Information

Background Information .:. About Projectile Motion .:. Statement of Problem .:. Hypothesis .:. Materials & Procedure .:. Analysis & Conclusion .:. Results .:. Bibliography .:. Return to Top .:. Return To Research

PROJECTILE MOTION

based on varying angles

Using a Pneumatic Cannon

Background Information

Pneumatics is the “use of pressurized gas to affect mechanical motion.” Pneumatic power if used in today’s industry where it is quite common to have factory units plumbed for compressed air; however, other compressed gases (that are inert) can be, and are used in smaller or self-contained systems. It is also used in a lot of industries such as dentistry, construction, or mining.

Pneumatic launchers are considered a little more difficult to build because there is the need to make it completely air tight—the construction must be precise. In general, these pneumatic cannons typically have four basic components: a filling valve, an air chamber, a pressure-release valve, and a barrel.

In a pneumatic spud gun, also known as a “potato gun”, air is pumped into the pressure chamber. After the specific pressure is reached, for example 40 psi’s, the pressure release valves open, which allows for the gas to go down the barrel, propelling the projectile forwards (in our case, it was a nerf gun “safety-cushioned” projectile, shaped like a tube or dart).

Range formula: R = (v^2 / g) * sin(2ө)

About Projectile Motion:

A projectile is any object that has been thrown, shot, or launched. The flight paths of these projectiles can be affected by two different factors: gravity and air resistance (Henderson, 2007). The effect gravity has on a projectile is fairly easy to understand. If there were to be no air friction, the projectile would fall at 9.8 meters every second. The projectile will gain height but because of gravity, its vertical velocity will become smaller and smaller until it reaches zero (Answers.com 2008). That is when it is at its maximum height. Then it begins descending and its velocity increases until it reaches the ground. If we had no air resistance, we could use this to predict the exact spot our projectile will land. But because we have no vacuum to work with, there will be air resistance. Friction from the air creates a slight drag on the projectile, which can cause it to fall slightly short of the expected distance. We will neglect air resistance and factor it into our uncertainty in this experiment.

Statement of Problem:

The purpose of this investigation is to compare the actual range with the predicted range of a spring-powered air soft gun pellet, shot at varying angles.

Hypothesis:

We believe that the actual range will be a slightly shorter range than the predicted range due to air friction acting on the projectile. Our independent variable is the changing angle in each trial. Our constant variables include mass of the projectile, the horizontal velocity, and the gun being used. Range will be defined as the horizontal distance that the projectile travels before hitting the level ground.

Materials and Procedure:

Materials:

- Nerf Gun dart (2)

- Pneumatic Cannon

- Tire pump containing pressure gauge

- Measuring tape (in meters, at least 300 feet)

- Workable protractor

- Logger-Pro computer software

- Video camera

- Level area

- Pen/Paper

- Calculator

Diagram

Procedure:

First we measured the angle of the pneumatic cannon. Then, we pumped air into the pneumatic cannon. Each time, we put in 40 psi, which is about three pumps from the tire pump. Next, we loaded the pneumatic cannon with the nerf gun dart and flipped the switch to open the pressure-release valve to release the air, thus forcing the nerf gun dart out. We measured from the tip of the cannon where the dart initially was, to where the dart first hit the ground. Then, we did four more trials of the same angle. We repeated this until we did it for all ten angles (0, 10, 20, 30, 40, 45, 50, 60, 70, 80). After we found all of our angles, we had to figure out the velocity of the dart at 40 psi. In order to do this, we shot the dart at a ninety degree angle in the air and recorded it on the camera. Then using logger pro, we were able to use SUVAT and figure out the velocity.

Results

Data File: Text | Excel

Analysis and Conclusion:

Our initial theory was that the actual range of the projectile (nerf-gun dart tube) would be slightly less than the predicted range, due to air resistance. In addition, the greatest distance covered by the projectile should be at, or around, a forty-five degree angle. After three separate trials, the distance the dart reached was approximately 30.6 meters. At this, the actual range at a forty-five degree angle should be 31.236 meters. All of our collected range distances tended to be less than the predicted ranges, which supports our theory (see attached data collection paper, to view predicted vs actual ranges) that air resistance affects range travel. Errors that could have also affected our experiment include: inaccuracy in measuring angles (form zero to eighty degrees), using a protractor, not measuring the same amount of pressure each trial (three different trials), as well as figuring out distance and measuring where the dart landed. For further research, we would most likely use a more accurate pressure gauge or base the experiment off the amount of pressure, instead of varying angles.

Uncertainty:

[ (highest-lowest) / 2] / (# trials)

Angle (Degrees) : 0

[ (8 - 6.9) / 2] / (3) = .1833 x 100% = 18.33% inaccuracy

Angle (Degrees) : 10

[ (11.5 – 9.1) / 2] / (3) = .4 x 100% = 40% inaccuracy

Bibliography:

[no author]. “Pneumatics.” 2009. <http://en.wikipedia.org/wiki/Pneumatic>.

[no author]. “Pneumatic Launchers.” 2009.

<http://en.wikipedia.org/wiki/Potato_cannon>.

Beckler, Matthew. “Pneumatic Cannon.” 2009. <http://www.mbeckler.org/pneumatic_cannon.html>.

Henderson, Tom. “Lesson 2: Projectile Motion.” The Physics Classroom Tutorial. 2007.