Name: high-speed optical diagnostics of a supersonic ping-pong cannon
Uploaded: 2023-03-24T13:10:00
Description: Watch this Scientific Journal Video about High-Speed Optical Diagnostics of a Supersonic Ping-Pong Cannon at JoVE.com

This work is supported by the NSF Division of Undergraduate Education (award # 2021157) as part of the IUSE: EHR program

1. Building and assembly of the ping-pong cannon (PPC)
<ol>
	<li>Assemble all the components of the PPC according to Figure 1.</li>
	<li>Insert two high-clarity acrylic windows in the sides of the cannon to allow for optical probing across the interior of the cannon.
	<ol>
		<li>Drill two 1/2 in holes through opposite sides of the PVC near the cannon&#39;s exit.</li>
		<li>Prepare two 1/8 in thick acrylic windows using a laser engraver. Download the three supplementary svg...

<ol>
	<li>Peterson, R. W., Pulford, B. N., Stein, K. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+ping-pong+cannon:+A+closer+look.">The ping-pong cannon: A closer look.</a> The Physics Teacher. 43 (1), 22-25 (2005).</li><li>Olson, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+shock+waves+in+expansion+tube+accelerators.">The role of shock waves in expansion tube accelerators.</a> American Journal of Physics. 74 (12), 1071-1076 (2006).</li><li>Cockman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+vacuum+bazooka.">Improved vacuum bazooka.</a> The Physics Teacher. 41 (4), 246-247 (2003).</li><li>Ayars, E., Buchholtz, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+the+vacuum+cannon.">Analysis of the vacuum cannon.</a> American Journal of Physics. 72 (7), 961-963 (2004).</li><li>Thuecks, D. J., Demas, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+the+effect+of+air-intake+aperture+size+in+the+ping-pong+ball+cannon.">Modeling the effect of air-intake aperture size in the ping-pong ball cannon.</a> American Journal of Physics. 87 (2), 136-140 (2019).</li><li>Liepmann, H. W., Roshko, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Elements of gas dynamics. , (1957).</li><li>Settles, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Schlieren and shadowgraph techniques. , (2001).</li><li>Geisert, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+single+mirror+schlieren+optical+system.">A single mirror schlieren optical system.</a> American Journal of Physics. 52 (5), 467 (1984).</li><li>French, R. M., Gorrepati, V., Alcorta, E., Jackson, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mechanics+of+a+ping-pong+ball+gun.">The mechanics of a ping-pong ball gun.</a> Experimental Techniques. 32 (1), 24-30 (2008).</li><li>French, M., Zehrung, C., Stratton, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+supersonic+ping-pong+gun.">A supersonic ping-pong gun.</a> arXiv. , (2013).</li><li>French, F., Choudhuri, R., Stratton, J., Zehrung, C., Huston, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+modular+supersonic+ping-pong+gun.">A modular supersonic ping-pong gun.</a> arXiv. , (2018).</li><li>Fredrick, C. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Complementary+studies+on+supersonic+nozzle+flow:+heterodyne+interferometry,+high-speed+video+shadowgraphy,+and+numerical+simulation.">Complementary studies on supersonic nozzle flow: heterodyne interferometry, high-speed video shadowgraphy, and numerical simulation.</a> WIT Transactions on Modelling and Simulation. 59, 223-234 (2015).</li></ol>

We have presented a method for the construction of a PPC and an SSPPC along with optical diagnostics for the measurement of ball velocities and for the characterization of shock propagation near the exit of the cannon. The standard PPC is constructed with a 2 m section of 1.5 in schedule 80 PVC pipe. The pipe is fitted with flanges at each end, quick-connect vacuum fittings, and acrylic windows near the exit for laser diagnostics. A detailed schematic of the PPC is shown in Figure 1. Prior t...

The PPC is a popular physics demonstration used to show the immense air pressure to which people are continually exposed1,2,3,4,5. The demonstration involves the placement of a ping-pong ball in a section of pipe that has an inner diameter that is approximately equal to the diameter of the ball. The pipe is sealed off on each end with tape and evacuated to an internal pressure of less than 2 Torr. The tape on one end of the pipe is punctured, which allows air to enter the cannon and causes the ball to experience peak accelerations of approximately 5,000 g&#39;s. The ball, which is accelerated by atmospheric pressure alone, exits the cannon at a speed of approximately 300 m/s after traveling 2 m.
Although the PPC is commonly operated as a simple demonstration of atmospheric pressure, it is also an apparatus that exhibits complex compressible flow physics, which has resulted in numerous open-ended student projects. The dynamics of the ball are influenced by secondary factors such as wall friction, the leakage of air around the ball, and the formation of shock waves by the accelerating ball. The substantial acceleration of the ball introduces a large-amplitude compression wave that travels down the tube in front of the ball. These compressions travel faster than the local sound speed, resulting in a steepening of the compression wave and the eventual formation of a shock wave6. Previous work has studied the rapid buildup of pressure at the exit of the tube due to the reflections of the shock wave between the ball and the taped exit of the tube and the resulting detachment of the tape prior to the exit of the ball2. High-speed video using a single-mirror schlieren imaging technique has revealed the response of the tape to the reflecting shock waves and the eventual detachment of the tape at the exit of the PPC7,8 (Video 1). Thus, the PPC serves as both a simple demonstration of air pressure that intrigues audiences of all ages and as a device exhibiting complex fluid physics, which can be studied in great detail in a laboratory setting.
With the standard PPC, the ping-pong ball speeds are limited by the speed of sound. This basic version of the PPC is covered in the scope of this paper, along with a modified cannon used to boost the ball to supersonic speeds. In previous work by French et al., supersonic ping-pong ball speeds have been achieved by utilizing pressure-driven flow through a converging-diverging nozzle9,10,11. The SSPPC presented here utilizes a pressurized (driver) pipe to provide a larger pressure differential on the ping-pong ball than is provided by atmospheric pressure alone. A thin polyester diaphragm is utilized to separate the driver pipe from the evacuated (driven) pipe containing the ball. This diaphragm ruptures under sufficient gage pressure (generally 5-70 psi, depending on the diaphragm thickness), thus accelerating the ping-pong ball to speeds up to Mach 1.4. The supersonic ping-pong ball produces a standing shock wave, as can be seen using high-speed shadowgraph imaging techniques7,12 (Video 2).
A low-power (class II) HeNe laser is used to carry out optical diagnostic studies on the performance of the cannon. The HeNe laser beam is split into two paths, with one path traversing through a set of acrylic windows near the exit of the cannon and the second path traversing just past the exit of the cannon. Each path terminates on a photoreceiver, and the signal is displayed on a dual-channel oscilloscope. The oscilloscope trace recorded during the firing of the cannon reveals information about both the speed of the accelerated ping-pong ball and the compressible flow and shock waves that precede the exit of the ball from the cannon. The speed of the 40 mm diameter ping-pong ball at each beam location is directly related to the time the ball blocks the beam. A sensitive &#34;knife-edge&#34; shock detection setup is achieved by covering half of the detector with a piece of black electrical tape and positioning the edge of the tape at the center of the beam2. With this setup, slight deflections of the He-Ne laser beam, produced by the compressible flow-induced index of refraction gradients, are clearly visible as voltage spikes on the oscilloscope trace. The shock waves traveling toward the cannon exit and the reflected shock waves deflect the beam in opposite directions and are, therefore, identified by either a positive or negative voltage spike.
Here, we provide instructions for the construction and utilization of an optimized PPC and SSPPC, as well as optical diagnostic techniques (Figure 1, Figure 2, and Figure 3). The optical diagnostic techniques and measurements have been developed through previous years of study1,2.

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high-speed optical diagnostics of a supersonic ping-pong cannon

The traditional ping-pong cannon (PPC) is an educational apparatus that launches a ping-pong ball down an evacuated pipe to nearly sonic speeds using atmospheric pressure alone. The SSPPC, an augmented version of the PPC, achieves supersonic speeds by accelerating the ball with greater than atmospheric pressure. We provide instructions for the construction and utilization of an optimized PPC and SSPPC.
Optical diagnostics are implemented for the purpose of investigating the cannon dynamics. A HeNe laser that is sent through two acrylic windows near the exit of the pipe is terminated on a photoreceiver sensor. A microprocessor measures the time that the beam is obstructed by the ping-pong ball to automatically calculate the ball's velocity. The results are immediately presented on an LCD display. 
An optical knife-edge setup provides a highly sensitive means of detecting shock waves by cutting off a fraction of the HeNe beam at the sensor. Shock waves cause refraction-induced deflections of the beam, which are observed as small voltage spikes in the electrical signal from the photoreceiver. 
The methods presented are highly reproducible and offer the opportunity for further investigation in a laboratory setting.

Here, we provide instructions for the construction and utilization of a PPC and an SSPPC, along with the implementation of the optical diagnostics for shock characterization and velocity measurements. Representative experimental results are also provided. The completed systems of the PPC and SSPPC, along with necessary accessories, are shown in Figure 1 and Figure 2. The SSPPC is an augmented version of the PPC, where a driving, pressurized section of pipe is co...

Watch this Scientific Journal Video about High-Speed Optical Diagnostics of a Supersonic Ping-Pong Cannon at JoVE.com

High-Speed Optical Diagnostics of a Supersonic Ping-Pong Cannon

We describe a method for the construction of a supersonic ping-pong cannon (SSPPC) along with optical diagnostic techniques for the measurement of ball velocities and the characterization of propagating shock waves during the firing of the cannon.

The traditional ping-pong cannon (PPC) is an educational apparatus that launches a ping-pong ball down an evacuated pipe to nearly sonic speeds using ...

We provide instructions to construct and operate a supersonic ping pong cannon along with optical diagnostic techniques for measuring ball speeds and detecting shockwaves. The optical knife edge setup is highly sensitive to small, traverse deflections of a laser beam and provides a means for detecting shockwaves associated with the cannon. To begin, power the photo receivers and laser module by connecting them to a 15 volts current limited power supply and laser power supply.Then, attach the photo receivers to the two channels of the oscilloscope using BNC cables. For optical diagnostic setup, place the laser perpendicular to the fabricated cannon with the first beam traversing through the acrylic windows inside the pipe, and the second just outside the cannon exit. Place black electrical tape over half of the photo receiver sensor, creating a knife edge shock detection setup.To avoid clipping, adjust the beam position on the knife edge so that the baseline voltage is approximately 50%of the maximum. Next, adjust the settings on the oscilloscope to collect 20 million data points. Use the horizontal scale knob to set the data acquisition rate to 500 megahertz.Turn the trigger knob to trip at a voltage slightly below the set baseline acquired from the photo receiver. Before firing the PPC, wear ear and eye protection. Insert a ping pong ball into the exit of the cannon and blow lightly into the end of the cannon until it hits the vacuum fitting near the pipe entrance.Seal the cannon's exit flange and acrylic cap using two pieces of square tape. Ensure the laser beam is centered on the knife edge, the trigger is correctly positioned, and the catching container is secure. Turn on the vacuum pump to evacuate the pipe to a reduced absolute pressure of less than two Torr.Once a sufficient vacuum is reached, use a broadhead tip to puncture the tape at the entrance. After firing, turn off the vacuum pump and remove any remaining tape from the exit flange and the acrylic cap. For firing the supersonic PPC, close the valve connecting the driver pipe to the air compressor and fill the air compressor tank.Blow the ball, as previously demonstrated. After sealing the supersonic PPC exit flange, insert a thin precut polyester diaphragm between two rubber gaskets and place them between the cannon's driver and driven sections. Connect the two sections using four cam clamps.Once pressure is reduced in the pipe, release the pressure from the air compressor into the driver pipe, allowing pressure to increase until the diaphragm ruptures and the compressed air within the driver pipe fills the evacuated driven pipe. After the supersonic PPC firing, turn off the air compressor and the vacuum pump. Remove the ruptured polyester diaphragm and tape from the cannon.The propagating shockwave, reflected throughout the cannon firing process, was represented by a change in voltage with respect to time. A positive or negative spike demonstrates the direction of the shockwave in the signal, and velocity was calculated through the square pulse width, produced by the ball cutting off the beam. A microprocessor was used to process the signal from the beam transversing the pipe interior to automatically calculate and display the ball velocity near the cannon exit.The oscilloscope traces demonstrated the dual channel firing of the supersonic PPC. The upper trace represents the beam traversing the cannon interior, near the exit. Whereas the lower trace corresponds to the beam traversing the ping pong ball path after exiting the cannon.A cutoff signal indicated that the ball passed and obstructed each beam. The plot of pressure differential versus Mach number revealed that 0.001 and 0.002 inch thick diaphragms rupture at sufficient pressure differential to accelerate the ping pong ball to supersonic speed. The ball speed was consistently greater than Mach 1.3 with a 0.002 inch thick diaphragm.The presented supersonic ping pong cannon and the optical diagnostics will enhance the value of the cannon, both as a demonstration device and as an apparatus for follow-on laboratory experiments.

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Writing Bragg Gratings in Multicore Fibers

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Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and ...