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"Rest, in physics, refers to an object being stationary relative to a particular frame of reference or another object." - Wikipedia (emphasis mine) While on Earth, the planet is often treated as the default frame of reference. It is not a perfect frame of reference, but for many purposes it is good enough. Since there is no absolute frame of reference, ...


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"A state of rest" is a relative term. Relative means - measured in comparison to the things around it. When you sit in a train and sip from a cup of coffee, you can do so because the cup is still relative to you even though both of you might be hurtling through the countryside at 200 km/h. For most experiments, objects can be considered "at rest" if they ...


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Revolving around the sun is equivalent to free fall around the sun, so the revolution allows you not to 'feel' the sun's gravity. The rotation of the earth is something that can be measured: (i) a centrifugal force which is a small offset on gravity, and (ii) causes the coriolis force. Both these are small effects, so can often be ignored for laboratory ...


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When you're in a moving vehicle and see trees or buildings, who is moving? Are you moving forward, or are the trees and buildings moving backward? Its counter-intuitive for beginners but both these views are absolutely correct. We can only describe the motion of an object from a reference frame. A reference frame is a specific configuration from where you ...


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Solving lots of physics problems involved you choosing a frame of reference. As long as all your formulations are from a particular frame of reference, for example the energy of objects then the laws will work. Since you are also travelling with the object, (as the earth rotates) it is easier to say you are at rest. If you are travelling at constant velocity ...


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In non-eq stat mech the comment above isn't what they mean. We have to establish 3 separate things: Balance This is the condition that all transitions into and out of a state 'balance' ie $$ \sum_x p(x)k(x,y)=p(y) \quad \forall y$$ This ensures a stationary state, but nothing else Detailed balance This is the condition that all transitions ...


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When the light hangs off the ceiling by means of the electrical cable, the cable actually acts as a very stiff spring. The light bulb provides a downward force due to its weight $mg$. The cable acts like a spring, slightly idealised here as a Hookean spring which provides the counter force (what you called the force of tension) of $k\Delta y$ with $k$ the ...


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The simple word is "damping". Initially when you hang an object from a string (spring, etc), it will move - side to side, and up and down. While it is moving, there will be a changing force on the object - after all it is accelerating / decelerating. This shows up as a force in the string that changes with time. In all "real" systems, there is also a ...


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It's a general consequence of Newton's Laws of Motion that an object is stationary when no net forces or momenta act on it. Avoiding net forces or momenta is precisely what makes perfectly balancing a rectangular block on a triangular one so difficult. Above is a rectangular block with mass $m$, perfectly balanced on a triangular block. I've added the ...



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