Acceleration of a pumpkin from an air cannon

[philip porhammer]

Summary: what is the equation for a pumkin's acceleration when the air pressure in not constant.

My Daughter and I are going to Pumpkin chunkin for the first time.
I would like to get two orange shirts and scribble:
what part of this don't you understand:
(DifEq?) acceleration of a pumpkin from an air cannon. acceleration is not constant.
I will draw out an air cannon. this is only for my daughter and I. not making any for sale. just having fun!
will post a pic here from the event...

 

[anorlunda]

Pumpkin chunkin

Good for you. That sounds like a great activity for father and daughter.

The first principle equation is the familiar f=ma. But the devil is figuring out what f is. You'll find that it is not a simple formula, but a long list of equations with unknown coefficients.

I am very skeptical that the analytic approach will be much help with pumpkin chunkin. Learn from others; watch lots of Youtube videos; experiment. There is still lots of room for experimental physics/engineering in this world.

 

[philip porhammer]

air cannon theory has good equations! thanks!

 

[jedishrfu]

Like so many things today, there's a tool for this and an app for that. In this case, there's a calculator for pumpkin Chunkin:

http://www.iconico.com/ultimaCalc/punkin_balllistics.aspx
First I imagine the launch force will be constant for all pumpkin shots so that means that by measuring a few shots you could get the equations calibrated. From there, knowing the weight of the pumpkin (can you weigh it?) and the angle of the shot you could figure the distance. Also remember that since the pumpkin isn't a point particle that there is air drag that will blunt the parabolic trajectory of a perfect shot.

 

[philip porhammer]

I just looking to make a t-shirt for my daughter and I with some equations and an air cannon, thantks

 

[jedishrfu]

But wouldn't it be cooler to actually win and then you could sell tons of the t-shirt that made it all possible. :-)

 

[gmax137]

wiki "projectile motion"

scroll down to the section
Trajectory of a projectile with air resistance

Look for equations sx (this is the horizontal distance reached). That ought to be good enough for a tee shirt

 

[jedishrfu]

Here's some slides with projectile motion and graphs for your t-shirt (just add a pumpkin somewhere):

http://hydrogen.physik.uni-wuppertal.de/hyperphysics/hyperphysics/hbase/traj.html