### Vacuum Bazooka [ Version 2.0 ]

Presenter: Tony Wayne, Albemarle High School, twayne[at symbol]albemarle.org.

Va. SOL:
PH.7 The student will investigate and understand properties of fluids. Key concepts include
density and pressure.

National Standards:
Fluids and pressure
Topic/Concept
Shows that pressure exerts a force and balance of pressure
Materials

 • Vacuum Bazooka • PingPong(tm) ball • Vacuum pump • 3” wide sealing tape (Staples) • Screw driver

Safety Considerations
• The bazooka shoots a ping pong ball in excess of 600 mph!!! Don’t have anyone stand in front of it. Have a everyone stand far away. It will bounce off the wall it hits. It you drop or damage the pipe in ANY way. Get a new pipe. Irregularities, nicks and cracks can cause the pipe to implode and send pieces flying. Inspect the pipe before creating the vacuum.
• The initiation of the vacuum release is loud. Everyone should protect his or her ears.
• When dealing with vast differences in pressure, there is always a risk of implosion. BE SAFE. Always think of the students’ safety first. Keep the students far away from the pipe. Use it at your own risk. ( I assume no responsibility for your use of this design since I cannot oversee it’s safe use or construction. )

Presentation
Get a student volunteer to place the pingpong ball in the front of the bazooka. It will roll down the pipe until it hits the air stem inside. Place a piece of 3” sealing tape across the front and another piece against the rear. It needs to make a tight seal. Aim it towards a sturdy wall. Not towards a door, window or student. Pull the sides of the tape down on the pipe to hold it in place. Connect the vacuum pump. Keep your fingers away from the front and rear of the pipe now. You don’t want it to accidentally fire and do damage to your fingers or students. To “fire” the bazooka, stab the tape at the rear end with a screwdriver. It will ricochet off the wall it hits and make a VERY loud noise Then give the student worksheet to the students. It is a problem based on this demonstration.

How the physics is demonstrated

When the student removes her hand. The pressure is unbalanced. The 1 atmosphere of pressure at the rear of the bazooka pushes the ball forward.

Construction and Tips Regarding the Demonstraton

Here is a calculation you can do. I give this out as a student handout.

To find the speed, use kinematics. But you will need “a.”
To find “a” use F=ma
To find “F” use P=F/A. “A” is the cross-sectional area is the ball.
NOTE: You could use energy instead of kinematics to solve.

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