ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: Tomanomanous on September 24, 2011, 02:23:19 pm
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I don't know. This question confused me on Newtons Third Law of Motion:
Two students, James and Tania, are discussing the
forces acting on a lunchbox that is sitting on the
laboratory bench. James states that a weight force
and a normal force are acting on the lunchbox and
that since these forces are equal in magnitude but
opposite in direction, they comprise a Newton’s third
law action–reaction pair. Tania disagrees saying that
these forces are not an action–reaction pair. Who is
correct and why?
Could someone please tell me the answer and explain how they got it? It'd be much appreciated. Thanks!
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Tania is correct; this is not an example of an action/reaction pair. Such pairs of forces must act on *different* objects, whereas here the object acted on - the lunchbox - is the same for both forces. That is, the normal force acts on the lunchbox, and so does gravity (i.e. the weight force).
The 'reaction' force to the weight force is actually the force that the lunchbox exerts on the Earth. That is, the Earth exerts a gravitational force on the lunchbox, and the lunchbox exerts a force equal in magnitude but opposite in direction on the Earth.
I hope that helped :)
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Recall that Newton's third law pairs have to act upon two different objects.
The forces that James describes both act upon the lunchbox.
Therefore Tania is correct.
edit: beaten
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I am not too sure if this is the right place to ask a Year 11 Physics Questions.
How are plane mirrors constructed? (If not relevant to Year 12, Don't Worry! :) )
How can I find the gradient of a line if the axis is sin(i) versus sin(r)? (y2-y1/x2-x1 = m)?
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I am not too sure if this is the right place to ask a Year 11 Physics Questions.
How are plane mirrors constructed? (If not relevant to Year 12, Don't Worry! :) )
How can I find the gradient of a line if the axis is sin(i) versus sin(r)? (y2-y1/x2-x1 = m)?
Not sure about plane mirrors!
But the gradient of the line of sin(i) against sin(r) is just the ratio of the diffractive indicies
so the refractive index (n) of the "after refraction" medium over the refractive index of the "before refraction" medium = gradient
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I was under the impression that plane mirrors were something like a layer of glass coated with some sort of reflective material.
I think the ancient Greeks/Egyptians (not sure which) used to polish bronze or copper to produce mirrors. I think the method we use today is slightly more complex.
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I was under the impression that plane mirrors were something like a layer of glass coated with some sort of reflective material.
I think the ancient Greeks/Egyptians (not sure which) used to polish bronze or copper to produce mirrors. I think the method we use today is slightly more complex.
That's correct, a plane mirror will just be a flat polished piece of metal (often aluminum, sometimes silver) that can be covered with glass to protect it. You do not need to understand how it reflects light, that involves electrodynamics (2nd/3rd year uni).
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This is quite funny, how is knowing that a flat polished piece of metal is what a mirror is made of, in any way, aid in the understanding of physics? :P
VCE Physics = Physics Minus the Maths = Random and Irrelevant Facts :D