Date: Sun, 21 Nov 2004 07:29:13 -0500

Author: "Thomas J. Bauer"

Subject: Re: vacuum bazooka velocity

Post: writes:
>Hi guys,
>Thanks for giving the ideas to having my vacuum bazooka worked 100%
>successful. But I have trouble now for measuring the velocity of the ball
>coming out of the tube. I used two photogates with a smart timer
>(PASCOís). I recorded the distance between the two gates and tried to get
>the time from the timer. Because of the ball goes too fast to pickup the
>time, or what? It just failed. I tried to use laser switches instead of
>the photogates, the timer still didnít pickup the data. Do I miss
>something here? It seems a simple measurement? Any suggestions will be
>greatly appreciated.
>Have a good weekend all.

Two suggestions for measuring the ping pong velocity.

1) Use a strobe light directeds along the path of the ball. Set a video
camera to view about 3m of the path of the ball after it leaves the
bazooka. Set up a known distance mark along the path of the ball. I used
the end of the bazooka and a cart at two meters. Set the strobe to 300Hz
(I have a Pasco strobe that does this) Video tape the ball as it leaves
the bazooka. Play back frame by frame and one field will contain a high
speed photo of the ball. This works with digital or tape recorders.
Digital is nice because you can analyze the photo right away with software
like Video Point.

2) Make a ballistic Pendulum. I used a 4"diameter paper shipping tube with
a wood plug at one end. The mass of the catcher is about 3.5 kg. I
suspended it from a camera tripod so the length of the pendulum was about
two meters. Place a couple layers of paper over the open end of the tube
to catch pieces of the ball from leaving the catcher. Keep the end of the
catcher about a meter away from the bazooka so that the out rushing air
does not disturb the pendulum.
To measure the swing of the pendulum, use a small rod held so that it can
slide with little friction and positioned against the cathcer.

I have get equivilent velocities of about 200m/s with both methods.

Tom Bauer
Wellesley College

From Sun Nov 21 08:14:38 2004