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These last weeks many of us have been following the olympics.
I was watching the canoe races and was impressed by the skill and energy of athletes.

I thought if an olympian would have several boomerangs and the skills to be able to throw them in a way that he can get them back. If he repeats this throwing in a regular pace say once per second, could he get propulsion out of this chain of action like a rocket engine and make the canoe move? Assuming he is skillful enough to throw them in a way that they burn most of their energy in the air as drag?

Example and some numbers
So he ejects them with high speed and retrieve them with low speed?
lets say an efficient boomerang thrower uses 1 kilogram boomerangs and throw them at a speed of 36 kilometers/hour at a rate of one per second. So he is exerting $ E=1/2 (1.(9.8)*(36*1000/3600)^2= 500 watts $ which is beyond our dream but Olympians may be able to do it.
If he can make them come back and land gently on the basket he has for them he can produce o.7 horse power! It would be an exciting game to watch.

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  • $\begingroup$ From what I found on the net the speed of the boomerang is about constant, and cannot be tuned . The motion of the boat will be another complication. It is not clear that the boomerang will undershoot so as to be caught further forward than the original throw point. Possibly special design boomerangs might. And then again possibly not. $\endgroup$ – anna v Aug 23 '16 at 5:19
  • $\begingroup$ Interesting thing is the speed of boomerang really doesn't matter beyond the release point. it's just a media to let the arm of the Olympian work creating the momentum, which will have equal momentum in opposite direction on canoe. For all intensive proposes we could consider the boomerangs as a bucket which he fills with water and throws out fast, albeit the boomerang idea would be nicer for a YouTube video clip. How ever I believe the ballasting the airfoils and designing the pitch and angle and aspect ratio of the boomerang will change its flight and momentum loading or handling properties! $\endgroup$ – kamran Aug 23 '16 at 6:06
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In theory he could. The trick would be that he would need to throw the boomerang in such a way that it bleeds off much of its momentum to the air before being returned. If the Olympian did so, they would be able to generate thrust.

A highly related Mythbusters video: Can you blow your own sail.

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