I've been across a lot of questions like these, but I'm never quite able to get them. In this question, I reasoned that if I consider the boat and the fan to be a system, then there is actually no external force acting on it, so there is no reason for it to move. But, I have this gut feeling that the boat should actually move, but I'm not able to convince myself of this mathematically.
Help will be appreciated. Do try and really break it down for me. I'm an eleventh grader, and I've only just started delving into the realms of physics. If your fan-boat is in vacuum, they won't move. In the air, they will. Your assumption conflicts with your intuition is because you isolated the system from the air, which should not. The boat may obviously move forward.
That's how airplanes move, too. The turbines etc. A more interesting fact is that it may also move forward by creating "wind in the forward direction" by its own fan if this wind is reflected from the sail. There exist many approximate pictures in which the forces are guaranteed to cancel but none of those calculations is quite exact in the real world.
Ultimately, there have to be terms that don't cancel in the real world. And these terms have a similar effect on the boat as the motions of our hands when we swim. Swimming clearly doesn't contradict the laws of physics. When we push our hands through water behind our bodies, we are creating a higher pressure of the water on the rear side and lower pressure on the front size of the hands.
That's why the net force goes forward. One may imagine that the air is composed of "particles" it's the atoms in the air but imagine it's marbles and the fan is picking them from the air, shooting to the sail in front, and they get reflected from the sail. The reason why the boat is moving to the front is that the marbles it shoots are ultimately moving "mostly backwards", after they're reflected from the sail, but when they're picked from the fan, they're more or less caught as "marbles coming from all directions".
So the boat is changing the marbles' velocity to be "more to the back" after the maneuver than before that which is why the boat itself is moving forward.
This picture of "marbles" would completely disagree with ideal fluids etc. If all fluids air and water were perfectly ideal etc.
But the nonzero viscosity and similar things makes the fluids behave "a little bit as if they were marbles", and a little bit of this effect is enough to get the boat moving. The fan moves air pushing it from the front of the boat to the back.
Conservation of momentum say that "if something moves one way, something else must move in the opposite direction".
In this case - air moves back, boat moves forward. If you were holding the fan in your hands you would feel a force as it is pushing against the air. With the help of sound expert, they found that the suppressor reduced the sound level considerably, from to decibels for the. Jamie blew up a car rigged with primer cord and 2 gallons of gasoline. He, Adam, and the sound expert observed that the movie explosion had a longer duration and covered a wider range of frequencies than the real sound.
A second attempt, using 2. Previous: Episode Torpedo Tastic. The movie sound effect of a punch sounds like its real-world counterpart. The movie sound effect of a gun fitted with a silencer a.
Then the boat feels the full reaction force pushing forwards. This is how those swamp boats work. In that case, I say we throw the fan overboard well, attach it astern on the boat and have the blades of the fan thrust the boat forward using water as a propellant instead of air!
I aint no engineer, never mind an english major, but isn't driving a propeller through water more efficient than having it push air? Extra credit, due Monday. Mike W.
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