Physics Question

Amp34 said:
It makes oh so much sense, although it would be better slightly modified. A single prop boat with tide/wind pushing it at an accelerating pace to the left. :p
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Except that wind or a tide would not give rise to constant acceleration, the rate of acceleration would decrease as it approached the speed of the tide or the wind - i.e. if the side wind speed was 30mph then the boat could never exceed or even reach 30mph.

Otherwise speed boats would have sails rather than engines and the global energy crisis would be solved :)

The boat with 2 props and no water resistance is better, although even a prop can't provide constant acceleration.

In fact I don't know what can, even a spaceship with super rocket boosters is going to make this all messy as it approaches relativistic speeds.

Hope this helps :D
 
Ok, now I've got my head round the actual question by ignoring the fact it's a plane and imagining it's something else which has constant thrust and drag factors, lift acting at an agle and mavity acting straight down... (we'll call it a pigeon...)

By assuming that the vertical component of the lift is still equal to the mavity component, my initial thoguhts would be that it would continue in a stright line without going up or down (as specified by the OP). however, because we're imagining this as a plane, and ignoring all the other forces and laws of aerodynamics, the horizontal component is the only other factor to consider. In a real plane obviously you would slide to the right without any rudder input due to this horizontal component of the lift. Int his situation we're obviously ignoring this.

With everything being constant, no drag force to slow the aircraft, no unbalanced force between vertical lift and mavity, the only unbalanced force is the horizantal component. Therefore, with this being constant, the aircraft will either go into a constant circle or simply fly in a diagonal line. I can't decide which as the turning motion is usually induced by operation of the elevators to maintain altitude in a turn, but we're ignoring the altitiude in this question...

The graph shown overleaf makes no sense to me as there is nothing slowing the aircraft down, jsut the constant forces mentioned above..

I will admit to having skipped over the majority of the pages as I was confusing myself, and I've spent too many hours fixing aircraft, setting up flying controls and messing about on flightsim to try and understand some of the arguements here...:D

It's a question of balanced and unbalanced forces, not aerodynamics IMO...
 
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The graph overleaf makes perfect sense - at each timestep the plane moves forward 5 squares, so moves forward at constant velocity since there is no net force in that direction. It isn't slowing down. The force is sideways, which gives an acceleration sideways which is why at each timestep the sideways movement is bigger and bigger.
 
jimmymctavish said:
Except that wind or a tide would not give rise to constant acceleration, the rate of acceleration would decrease as it approached the speed of the tide or the wind - i.e. if the side wind speed was 30mph then the boat could never exceed or even reach 30mph.

Otherwise speed boats would have sails rather than engines and the global energy crisis would be solved :)

The boat with 2 props and no water resistance is better, although even a prop can't provide constant acceleration.

In fact I don't know what can, even a spaceship with super rocket boosters is going to make this all messy as it approaches relativistic speeds.

Hope this helps :D
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SiriusB said:
A tide makes more sense I guess. I was trying to keep it simple before someone started mentioning phases of the moon and whether or not it was morning or evening blah blah blah. Pedantic lot in here! :p

Excellent graph and proves that my boat rules. Stupid aeroplane :eek::D
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There you go SiriusB...:p

Amp34 said:
Ha, yeah I didn't think of that (although the only reason I could think of a tide accelerating was just after it had turned, but I doubt it would do so so uniformly... :p).

The original question is a perfect exam question however, way, way, way to complicated for what it is actually asking. As usual the hardest part is actually understanding what the question is actually asking you to do. :D
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jimmymctavish as you can see, we already discussed that. :p Also there would be no rate of acceleration as it reached the speed of the tide, as the boat is in the water (as long as there are no other forces acting on it other than water resistance and the tide) you will be going the speed of the tide straight away (you are essentially just another water particle). As I mentioned in the quote as well, if the tide had just changed you could have an acceleration up to the maximum flow of the tide, which could take a while so it's a perfectly feasable option, unless we are talking about t=infinity, which there is no need to do.

EDIT: But yeah, it's all about compromise a bit, and far better than the plane idea. :D
 
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jimmymctavish said:
The graph overleaf makes perfect sense - at each timestep the plane moves forward 5 squares, so moves forward at constant velocity since there is no net force in that direction. It isn't slowing down. The force is sideways, which gives an acceleration sideways which is why at each timestep the sideways movement is bigger and bigger.
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Yup, I think I get it more now actually. As you say, it's an acceleration, therefore it will get bigger in the speed aspect every time it's measured. Again, thinking of this as an object, not an airplane, with all other forces balanced, it will accelerate to silly speeds sideways over time.

It's been far too long since I've done proper physics, as I'd got it in my head it going sideways at a constant speed due to the unbalanced force. This of course makes no sense, as an unbalanced force is an acceleration...

I concede the graph is perfectly accurate, and will hang my head in shame...

Which muppet said this was an airplane to start with? Or a boat...? :rolleyes:
 
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