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The rocket on the bottle

 The rocket on the bottle
Materials and mounting
instructions:		   a half litre plastic bottle, two straws with different diameters, some putty. Make a hole in the lid of the bottle and insert the smaller straw, trying to obtain a tight fit (eventually improve it with silicon sealer). Close the bottle. Plug one end of the larger straw with putty and slip it, from the other end, on top of the smaller straw.
How to play:   squeeze rapidly the bottle with both hands, directing the “rocket” in the desired direction. The activity can be turned into a game to obtain the largest distance of throw.
Physics:  
  • force and pressure: the force applied by the hands while squeezing the bottle, produces a pressure that propagates to the air in the bottle and inside the straws (Pascal’s principle),
  • the increase of pressure reduces the volume of the trapped air (Boyle’s law),
  • the larger pressure under the cap of the large straw pushes it and sets it in motion with a high velocity,
  • by squeezing, energy is transferred from the hands to the air in the bottle, as energy of compressed air, and from it to the rocket-straw as kinetic energy,
  • a larger distance of throw is obtained by a larger and faster energy transfer from the hands to the trapped air and from this to the straw-rocket.
Educational aspects:  
  • discover the relation between the force applied by the hands and the pressure of the air in the bottle (Pa),
  • discover the propagation of pressure in the air (Pb),
  • discover that compressed air can set things in motion (Pe),
  • discover energy transfers to and from compressed air (Ee),
  • measure the distances obtained in different throws (Sa)
  • compare with your expectations.
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Last modified: Thu Nov 16 11:30:10 CET 2000