Learn more physics!
Q:
If a sailboat, in calm air, had a fan mounted on the back, blowing air at the sail, would it/could it propel the sailboat forward? If so, why/why not?
I could see where the reflection of the air back off the sail might cause motion, but I can’t see how the forward motion of the fan air itself could do the job.
- Mark (age 50)
S. Salem NY
A:
Yup, you can make the sailboat move in this fashion, but there are some ways to set it up that will work better than others.
Pointing a fan mounted on the back pointing it straight at a sail
whose surface is perpendicular to the air coming from the fan. This is
very ineffective, as the fan pulls the boat backwards by shoving the
air forwards, and the sail pulls the boat forwards with almost the same
force by stopping the air again. The boat may not stay exactly
stationary, but it sure won't make much progress.
The best way to do this is to remove the sail entirely, and point
the fan so it blows air backwards. Then the boat feels the full
reaction force pushing forwards. This is how those swamp boats work.
Tom
(published on 10/22/2007)
Follow-up on this answer.
