question: How can a stream of air from a vacuum stabilise a ping-pong ball midair?
comment: Because when an object is introduced to airflow, the air travels on practically all sides of said object. A shape like a sphere is easier to do this with because there are no edges to stop, slow, or block the air from hitting all the surface area. So when you hold an airflow below an object, the center of airflow is the strongest, and gravity is pushing down on the top. Because a ping pong ball is effected by gravity less than something like a bowling ball, a less powerful airflow is needed. Hence why it floats, rather than infinitely rise or fall. It's both going up and down at the same time, keeping it relatively stable. The gravity pulls it down, but the airflow pushes it up and locks it in place due to the airflow moving around the surface area of said object.
passages: The Coandă effect can be demonstrated by directing a small jet of air upwards at an angle over a ping pong ball. The jet is drawn to and follows the upper surface of the ball curving around it, due to the (radial) acceleration (slowing and turning) of the air around the ball. With enough airflow, this change in momentum is balanced by the equal and opposite force on the ball supporting its weight. This demonstration can be performed using a vacuum cleaner if the outlet can be attached to the pipe and aimed upwards at an angle.
   In geometry, a body with a single stable resting position is called "monostatic", and the term "mono-monostatic" has been coined to describe a body which additionally has only one unstable point of balance. (The previously known monostatic polyhedron does not qualify, as it has three unstable equilibria.) A sphere weighted so that its center of mass is shifted from the geometrical center is a mono-monostatic body. A more common example is the Comeback Kid, Weeble or roly-poly toy (see left figure). Not only does it have a low center of mass, but it also has a specific shape. At equilibrium, the center of mass and the contact point are on the line perpendicular to the ground. When the toy is pushed, its center of mass rises and also shifts away from that line. This produces a righting moment which returns the toy to the equilibrium position.
   Prof. Masaaki Kumagai, who developed BallIP introduced another ball drive mechanism that uses partially sliding rollers
  
  . The objective of this design was to develop 3-DOF actuation on the ball using a low cost mechanism.
  
  Section::::System description.:Sensors.
   Section::::System description.:Ball and actuation.
  
  The ball is the core element of a ballbot, it has to transmit and bear all arising forces and withstand mechanical wear caused by rough contact surfaces. A high friction coefficient of its surface and a low inertia are essential. The CMU Ballbot and Rezero used a hollow metal sphere with poly-urethane coating. B.B. Rider used a basketball, while BallIP and Adelaide Ballbot used bowling balls coated with a thin layer of rubber.
  
  In order to solve the rather complex problem of actuating a sphere, a variety of different actuation mechanisms have been introduced. 
   The European "Hop!" balls appeared in the beginning of the 1990s and are still available. Made by Italy's Ledragomma/Ledraplastic, these are essentially the quality exercise ball with a handle attached. The sizes of these balls range from the "Hop! 45" to the "Hop! 66" (66 cm, about 26 in).
   A Parable begins at a ping-pong ball factory. Each ball is made in exactly the same way, and machines test them to get rid of anomalies. As the balls are being tested for their bounce levels, one bounces much higher than the rest. It is placed in a chute which leads to a garbage can outside the factory. It proceeds to bounce across town to a park, where it begins to bounce. Quickly, a cluster of ping-pong balls gather around it. It keeps bouncing higher and higher, until it doesn't come back. It concludes with the comment:br
   Section::::Trivia.
  
  The game features the penguin protagonist from Konami's earlier title "Antarctic Adventure" on the title screen and as a member of the audience in the game. This penguin would be later be known as Penta. In the introductory animation, a pingpong ball bounces along the table, and finally hits Penta on the head, who appears to faint.
  
  Section::::Ports.
   This was the principle employed by WW2-period British inventor Barnes Wallace when he developed the "bouncing bomb" used in the famous "Dam Busters" raid against the Ruhr District dams. He had been inspired by the story of a technique historically used by the British navy that bounced spherical canon balls off the ocean surface to achieve accurate hits against enemy ships. Wallace worked out the physics by bouncing marbles, steel spheres, and various sizes and shapes of balls across a pond and then a long trough before progressing to larger-scale experiments. Even solid steel balls would bounce across water.
   Generally, high-performance waterballs have little friction on the water, they are relatively small in size and density making them generally a handball size. With a certain amount of force they skip, bounce and glide in a straight line on the water surface and can travel fast and long distance. They can be projected on the water between players at a range of 3– 200 feet as there is very little friction slow them on the water surface – particularly the sealed waterball. Each time they bounce, skip or roll on the water surface, the inertia is reduced by opposing forces of gravity, friction, surface tension, surface drag.
   The single-screen levels are inhabited by enemies, who can be killed by the firing of one of the balls. When a ball hits an enemy, it will continue moving in the same direction, intervening walls, and pushing the player backwards slightly. Balls can also be pushed forwards or pulled backwards, including around corners. Once a ball is placed onto its pad, it can be still be moved. Also included is a small bonus Kick-Ball game for two players, which doubles as practice with the control system.
  
  Section::::Other Appearances.
   The most common serve is the same as in table tennis where the ball must bounce first in the server's side of the table and then on the receiver's one. A mistake in service gives a point to the opponent, this can happen when the ball hits the net, bounces on the server's court or on one of the server's obstacles and does not pass onto the opponent's court, or if it does not bounce on the opponent's court. If the ball touches the net upon service and passes onto the opponent's court, service shall be done again. .
   Section::::General characteristics.:Length of the game.
   Section::::Characteristics.:Short distribution time.
  
  On average, 1.5 seconds is required for the screen process to reach a steady state and for particles to cover the screen. This is induced by the circular motion. The rotary acceleration has a loosening effect on the particles on the deck. Centrifugal forces spread particles across the screen. With the combination of the gravitational component, the efficiency of small particle passing through aperture is improved, and large size particles are carried forward towards the discharge end.
  
  Section::::Characteristics.:Vibration separation.
   As a consequence, for example, within a shell of uniform thickness and density there is "no net" gravitational acceleration anywhere within the hollow sphere.
   Rolling ball sculptures rarely use circular-cross-sectioned tubes for the runs; tubes can induce balls to oscillate in ways that can introduce unpredictable delays; because of this, most sculptures use parallel guide rails on either side of the ball.
  
  The tallest rolling ball sculpture in the world, at tall, is said to be the "Energy Machine", located in the Hong Kong Science Museum in Hong Kong.
  
  Section::::Toys and kits.
   The physics of the operation of the pop pop boat is very similar to that of the "Feynman sprinkler," a submerged sprinkler which is seen to turn weakly or not at all as water is sucked in through it. In both cases, the reaction force on the solid device caused by the sucking in of the fluid is balanced by the fluid impinging on the inside of the device.
  
  Section::::See also.
  
  BULLET::::- Steam engine
  
  BULLET::::- Pulse jet engine
  
  BULLET::::- Valveless pulse jet
  
  BULLET::::- Feynman sprinkler
  
  Section::::External links.
  
  BULLET::::- The Pop Pop Pages including extensive references and vendors
  
  BULLET::::- 4Physics.com description
   A sealed ball displaces and bounces on water as it interacts with the water surface. On impact with the water surface or a player's hand, the sealed waterball deforms and deflects and transfers its energy in the opposite direction as it bounces on impact. But a sealed waterball no matter how soft still maintains its spherical shape and ball like properties. The fluid dynamics and shape characteristics are relatively unchanged as the sealed waterball does not change its density.
   In addition to leading Geomagic, Fu has held a number of advisory roles relating to technology and entrepreneurship and with charitable organizations. She has served on the U.S. National Advisory Council on Innovation and Entrepreneurship since 2010 and is also a member of the National Council on Women in Technology. In 2012, she was appointed to the board of the Long Now Foundation, a non-profit organization focused on long-term thinking and enduring technology. She also serves on the board of the Frank Hawkins Kenan Institute of Private Enterprise at the University of North Carolina, the board of Live Nation Entertainment and is an advisor at Modern Meadow, an organization focused on tissue engineering.
   A hollow ball in latex revolves around a metallic mast (1,70m high) which is linked by a nylon thread (fishing thread type) of 1,70m length. The thread is knotted to the mast by a loop or a plastic ring freely revolving around a reel. The mast is fixed in a base from 40 kg to 90 kg. The ball is elliptic and is hit with a rigid plastic racquet with a small handle and a strings around 25 cm of diameter. The speed-ball court is about 6x4 m. for the single match and 8x6 m. for the doubles.
  
  Section::::Rules.
   The paddles and balls to be used also depend on the variety previously agreed upon for the development of the match or tournament. In the classic variations of pingpongo the traditional paddles and ball of ping pong are used.
  
  Section::::General characteristics.:Obstacles.
  
  Obstacles can be either tangible or intangible. Pingpongo has the stated purpose of promoting dialogue and consensus; thus, any obstacle must be determined by mutual agreement of the players of a given match or tournament.
   The space hopper is a heavy rubber balloon about in diameter, with two rubber handles protruding from the top. A valve at the top allows the balloon to be inflated by a bicycle pump or car tire pump.
  
  A child can sit on top, holding the two handles, and bounce up and down until the balloon leaves the ground. By leaning, the driver can make the balloon bounce in a particular direction. In practical terms, this is a very inefficient form of locomotion, but its simplicity, ease of use, low cost and cheerful appearance appeal to children.
  
  Section::::History.
   BULLET::::- Two or four players playing respectively single or double
  
  BULLET::::- One ballbag with weight or floor embedded hook
  
  BULLET::::- A qianball racket for each player
  
  BULLET::::- A qianball ball with rubber band
  
  BULLET::::- A net or similar at a height of 81 cm
  
  The game is played by placing the ball bag 2.1 m from the net in the so-called Qianball point. the end of the rubber band is attached to the turning rings or the floor embedded hook. 
   Section::::In Laos.
   A close terrestrial analogy is provided by a tennis ball bouncing off the front of a moving train. Imagine standing on a train platform, and throwing a ball at 30 km/h toward a train approaching at 50 km/h. The driver of the train sees the ball approaching at 80 km/h and then departing at 80 km/h after the ball bounces elastically off the front of the train. Because of the train's motion, however, that departure is at 130 km/h relative to the train platform; the ball has added twice the train's velocity to its own.
   BULLET::::- eXplore: In the underwater event, the manually-controlled robots dive and release several light weight balls held at different coordinates in a large water tank. The robots then collect the balls that are floating on the surface and bring them to the designed area of the arena called the victory zone.
  
raw_presuppositions: Ping pong ball should not be stable in air when in vacuum stream.
raw_corrections: Stream of air goes around the entire object and pushes it in as well as up against gravity. 