Projectile motion

[TheBigDog]

So this brings up another question. Should questions like these be in a text book that is supposed to be teaching?

 

I understand the value of asking hard questions, and getting students to sort out the eroneous information, but really, this question seems to be crossing a line. In a real world situation, should I need to calculate this angle, I would take all the measurements I needed. I would not tell myself, "Now this is projectile motion because the puck is moving in an arc across the surface of the table." If I didn't need that information.

CWES, After reading Kingwinner's next question...

 

http://hypography.com/forums/physics-mathematics/5665-projectile-motion-aiming-monkey.html

 

I think I understand the point of this one. It is trying to illustrate that the trajectory of the puck is irrelevant to the way that it is influenced by gravity. That is the lesson of the next question and King's current dilemma.

 

Bill

[Qfwfq]

Right King, a bit more than 4 degrees, although it isn't really necessary to use Newton's 2nd. You can do the trig and vector algebra directly on g since it's on the same mass.

[cwes99_03]

Degrees of freedom in classical mechanics means that, if there are n of them, then the configuration space is an n-dimensional differentiable manifold. Now, there are no two ways about that.:confused:

 

I would talk about tangent, not normal forces. The board is a 2-dimensional manifold embedded in the 3-dimensional one, effective g for the problem is therefore the tangent component of the vertical effective g.

 

For some finding the tangent forces is a snap and takes place automatically in the mind and out through the keyboard of the nearest calculator pops the first answer (which is in fact what the bloke is looking for so we must go no further). Thus if I then wanted to do any more work, say figuring out what kind of force across the surface of the board (which is now our 2-d manifold or plane) is necessary to cause the puck to accelerate in a straight line toward the corner of the table I could. However we are not asking that question, we are trying to find the tangent part of the normal force. Thus we are not interested in talking about tangent forces but finding them.

 

Now discussing n-dimensional manifolds and the like are well above the understanding of first-year students trying to understand the complexities of physics.

 

Big-Dog: That does simplify things a bit. I like questions that build on previous questions, but I'm not fully convinced that this happened here. Granted the section may be covering this sort of thing, but that was still an awful question in my mind. I can't really say without having the chance to look at the book myself. HOWEVER, it raises my initial point, that Kingwinner may need to do a bit more reading on his own to understand these things instead of getting someone else to always answer the question for him. Otherwise, I suggest he find another subject to study.

[Qfwfq]

Now discussing n-dimensional manifolds and the like are well above the understanding of first-year students trying to understand the complexities of physics.

That stuff was meant for you and TBD, who King prolly wasn't following. :confused: