# Launcher Design

## Main Question or Discussion Point

Do you guys think it is possible to build a spring launcher that launches a small projectile like a tennis ball or baseball like 600 feet...If it is, what kind of spring would one use.

Or maybe a different launcher approach would be better. LET Me Know

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600 feet....Up, downrange, what?

600 feet for a tennis ball is quite a ways. Does it have to be mechanical? You could try a pressure vessel, but I wouldn't recommend it if you have to prior experience with them. To launch a tennis ball 600 feet you'll need some high pressure, and that can be very dangerous.

You could build a large trebuchet, but the problem is that your tennis ball is pretty light and wont really get a great deal of momentum. (maybe a baseball...)

The energy stored in a compressed spring is:

U = 1/2 * k *x^2

k = spring constant
x = spring displacement from rest.

You could equate this to the potential energy of the tennis ball:

PE = m g h
m = mass of tennis ball
h = 600 ft

And you could find combinations of k & x and see if they are available.

Be carefull if you actually do this - it could be dangerous !

Due to atmospheric air drag, it would require about 1000 meters per second vertical launch velocity for a tennis ball to reach 600 feet elevation. The drag coefficient for turbulent drag is about 0.6 due to the fuzz.. For a baseball (hardball), about 130 meters per second is adequate. I had to use numerical integration as follows:

PROGRAM launchtennisball
REM vertical launch
OPTION NOLET
g=9.81 ! gravity
m=0.057 ! mass in kg
d=0.065 ! diameter in meters
C=0.6 ! drag coedfficient
dens=1.2 ! density of air in kg per m^3
v0=100 ! vertical launch velocity in meters per sec
CALL launch(v0,g,m,d,C,dens,ymax,t)
PRINT ymax,t
END

SUB launch(v0,g,m,d,C,dens,ymax,t)
v=v0
t=0
dt=0.001
A=pi*d^2/4
y=0
ymax=0
DO
t=t+dt
dv=(0.5*dens*C*A*v^2/m)*dt+g*dt
v=v-dv
y=y+v*dt
LOOP until v<0
ymax=y
END SUB

Bob S

LOL! I must say that college kids are probably a bit saner than we used to be. . . .

Google "spud gun" or "potato gun" or "beer can cannon". 600 ft might be a bit far for something as light in sectional density as a tennis ball, but. . . it HAS been done! :-) "Iron City" beer cans (steel with rolled rims) made for good barrel material but you could use tennis ball cans. Add on a healthy layer of fiber tape to make up for the lack of barrel strength. Add lighter fluid (naptha) a tennis ball and fire away! LOL! Recommendation: Tape the barrel to a stick of wood and you have a regular "hand cannone" of the 12th century variety! :-)