# Tag Info

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In my opinion "description of trajectory" is not a topic of physics it is a topic of kinematics (geometry of motion, see http://en.wikipedia.org/wiki/Kinematics). Whereas explaining the mechanism which causes an object to follow a particular trajectory IS a matter for physics. To say that "B goes around C" is to describe a trajectory in space and time. A ...

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We can do that using states of Matter. If temperature is frame dependent, the observers in different frames should observe different states of matter near Melting and Boiling points which is not the case. This was the easiest explanation I could think of.

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Acceleration need not be relative to any object. It is relative to space (/spacetime), which is like a universal coordinate system. Whenever you accelerate, there are signs. For example, imagine you are in an elevator in deep space. If you begin to accelerate upwards (in the direction normal to the top of the elevator car) at 9.8 m/s^2, you will begin to ...

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If you stick to gases then things are relatively straightforward because the temperature is related to the relative velocity of the gas molecules, that is the velocity of the gas molecules relative to each other. If you put your canister of gas in a fast moving (but non-relativistic) rocket moving at some velocity $v$ then you add the same velocity $v$ to ...

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Let us say you are in an inertial reference frame with a circular planar disk. If you take your meter measuring rods (or perhaps tape measure) you can find the diameter and circumference of the disk. Then the distance ratios between constituents of the disk edge can certainly be determined; and a midpoint of the disk may be identified (also in terms of ...

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"Newton's second law says F=ma. Now if we put F=0 we get a=0 which is Newton's first law. So why do we need Newton's first law ?" I don't think this is obvious from Newton's statement of the Second Law. In the Principia, he says that a force causes an acceleration. Without the first law, this doesn't necessarily imply that zero force means zero ...

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Newton's first law postulates that there is (at least) one inertial reference frame for every object, in which said object will continue in uniform motion unless acted upon by a force. Newton second law states that, within the inertial reference frame for any object, $F = ma$. Without the first law to assert that there is indeed a frame in which $F=0$ ...

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Inertial forces are considered non-assigned forces and thus are regarded as fictitious forces (even though they are real and the observer experiences these forces). They are mostly related to relative motion between (non-inertial, accelerated) frames of reference and transformation(s) thereof (eg centrifugal, Coriolis force, etc.. ). Apart from that, ...

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Instead of a disc, let's use a ring. Now remember it is a ring I refer to when I tell you to make a measurement. If you sit inside a ring, you aren't moving. Like sitting inside a hula hoop which someone is rotating around you without touching you by applying tangential forces on the hula hoop. Your metre sticks are always in a state of rest w.r.t. you or ...

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