The ping-pong ball water cannon
The course “Phy Ex” was created by Yves Couder in the Paris VII university to teach experimental physics through projects. In this article, we present this teaching method through a particular project that took place in the autumn semester 2019: the ping-pong ball water cannon. In this experiment, a...
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| Format: | Article |
| Language: | English |
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Académie des sciences
2020-11-01
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| Series: | Comptes Rendus. Mécanique |
| Subjects: | |
| Online Access: | https://comptes-rendus.academie-sciences.fr/mecanique/articles/10.5802/crmeca.46/ |
| _version_ | 1797651487522816000 |
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| author | Andreotti, Bruno Toutain, Wladimir Noûs, Camille El Rhandour-Essmaili, Sofia Pérignon-Hubert, Guillaume Daerr, Adrian |
| author_facet | Andreotti, Bruno Toutain, Wladimir Noûs, Camille El Rhandour-Essmaili, Sofia Pérignon-Hubert, Guillaume Daerr, Adrian |
| author_sort | Andreotti, Bruno |
| collection | DOAJ |
| description | The course “Phy Ex” was created by Yves Couder in the Paris VII university to teach experimental physics through projects. In this article, we present this teaching method through a particular project that took place in the autumn semester 2019: the ping-pong ball water cannon. In this experiment, a glass containing water and a floating table tennis ball is dropped from some height to the ground. Following the impact, the ball is ejected vertically upwards at speeds that can be several times the impact speed. We report the student team’s initial dimensional and order-of-magnitude analysis, and describe the successive experimental set-ups that showed (1) that free flight is essential for the phenomenon to occur, (2) that the order of magnitude of the ball ejection momentum is correctly predicted by a momentum balance based on integrating the pressure impulse during impact and (3) that making the ball surface more wettable, or stirring the liquid, drastically increases the momentum transfer. The proposed explanation, confirmed by direct high-speed video observations, is that the immersion depth of the ball increases during free fall due to capillary forces or vortex depression—in the absence of buoyancy—and that the enormous excess pressure on the bottom of the ball during impact drives the ball up towards its buoyancy equilibrium. The transfered momentum is sufficient to expel the ball at high velocity, very similar to the formation of liquid jets in collapsing cavities in liquids. |
| first_indexed | 2024-03-11T16:15:23Z |
| format | Article |
| id | doaj.art-a5734ea1cd5746aea6072ec5e6a39a1c |
| institution | Directory Open Access Journal |
| issn | 1873-7234 |
| language | English |
| last_indexed | 2024-03-11T16:15:23Z |
| publishDate | 2020-11-01 |
| publisher | Académie des sciences |
| record_format | Article |
| series | Comptes Rendus. Mécanique |
| spelling | doaj.art-a5734ea1cd5746aea6072ec5e6a39a1c2023-10-24T14:20:55ZengAcadémie des sciencesComptes Rendus. Mécanique1873-72342020-11-013486-742343710.5802/crmeca.4610.5802/crmeca.46The ping-pong ball water cannonAndreotti, Bruno0Toutain, Wladimir1Noûs, Camille2El Rhandour-Essmaili, Sofia3Pérignon-Hubert, Guillaume4Daerr, Adrian5Laboratoire de Physique de l’ENS, UMR 8550 Ecole Normale Supérieure – CNRS – Université de Paris – Sorbonne Université, 24 rue Lhomond, 75005 Paris, FranceMatière et Systèmes Complexes, UMR 7057 Université de Paris – CNRS, 10 rue Alice Domon et Léonie Duquet, 75013 Paris, FranceLaboratoire Cogitamus, FranceMatière et Systèmes Complexes, UMR 7057 Université de Paris – CNRS, 10 rue Alice Domon et Léonie Duquet, 75013 Paris, FranceMatière et Systèmes Complexes, UMR 7057 Université de Paris – CNRS, 10 rue Alice Domon et Léonie Duquet, 75013 Paris, FranceMatière et Systèmes Complexes, UMR 7057 Université de Paris – CNRS, 10 rue Alice Domon et Léonie Duquet, 75013 Paris, FranceThe course “Phy Ex” was created by Yves Couder in the Paris VII university to teach experimental physics through projects. In this article, we present this teaching method through a particular project that took place in the autumn semester 2019: the ping-pong ball water cannon. In this experiment, a glass containing water and a floating table tennis ball is dropped from some height to the ground. Following the impact, the ball is ejected vertically upwards at speeds that can be several times the impact speed. We report the student team’s initial dimensional and order-of-magnitude analysis, and describe the successive experimental set-ups that showed (1) that free flight is essential for the phenomenon to occur, (2) that the order of magnitude of the ball ejection momentum is correctly predicted by a momentum balance based on integrating the pressure impulse during impact and (3) that making the ball surface more wettable, or stirring the liquid, drastically increases the momentum transfer. The proposed explanation, confirmed by direct high-speed video observations, is that the immersion depth of the ball increases during free fall due to capillary forces or vortex depression—in the absence of buoyancy—and that the enormous excess pressure on the bottom of the ball during impact drives the ball up towards its buoyancy equilibrium. The transfered momentum is sufficient to expel the ball at high velocity, very similar to the formation of liquid jets in collapsing cavities in liquids.https://comptes-rendus.academie-sciences.fr/mecanique/articles/10.5802/crmeca.46/Scientific methodTeaching of researchFluid mechanicsHydraulic catapultShock wavePressure focussingLiquid projection |
| spellingShingle | Andreotti, Bruno Toutain, Wladimir Noûs, Camille El Rhandour-Essmaili, Sofia Pérignon-Hubert, Guillaume Daerr, Adrian The ping-pong ball water cannon Comptes Rendus. Mécanique Scientific method Teaching of research Fluid mechanics Hydraulic catapult Shock wave Pressure focussing Liquid projection |
| title | The ping-pong ball water cannon |
| title_full | The ping-pong ball water cannon |
| title_fullStr | The ping-pong ball water cannon |
| title_full_unstemmed | The ping-pong ball water cannon |
| title_short | The ping-pong ball water cannon |
| title_sort | ping pong ball water cannon |
| topic | Scientific method Teaching of research Fluid mechanics Hydraulic catapult Shock wave Pressure focussing Liquid projection |
| url | https://comptes-rendus.academie-sciences.fr/mecanique/articles/10.5802/crmeca.46/ |
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