Into the framework of Newtonian dynamics via the introduction of so-called fictitious forces-see Chapter 7.There was this fellow in England named Sir Isaac Newton. Furthermore, anyĭeviations of such a frame from a true inertial frame can be incorporated Possible to identify an approximate inertial frame. However, for a given dynamical problem, it is always To identify an absolute inertial frame-the best approximation to suchĪ frame would be one in which the cosmic microwave background appears Of the orbits from the predictions of Newtonian dynamicsĭue to the orbital motion of the Sun about the galactic center areįar too small to be measurable. To distant stars, is approximately inertial. In the Solar System, a reference frame whose origin is the center of the Sun, and whose coordinate axes are fixed with respect In this case, the deviation is due to the Earth's orbital Orbits are measured to extremely high precision then they willĪgain be found to deviate very slightly from the predictions of Newtonianĭynamics. Is the center of the Earth, and whose coordinate axes are fixed with respect Objects in orbit around the Earth, a reference frame whose origin Is due to the fact that the Earth is rotating, and its surface is thereforeĪccelerating towards its axis of rotation. Precision then it will be found to deviate slightly from the predictions If the trajectory of a projectile within such a frame is measured to high Respect to this surface is approximately inertial. If the first frame is an inertial frame then the second is not.Ī simple extension of the above argument allows us to conclude that anyįrame of reference which accelerates with respect to a given inertialįor most practical purposes, when studying the motions of objects close to theĮarth's surface, a reference frame which is fixed with Moving in a straight-line with constant speed in the first frame ( i.e., if According to the above formula, if an object is Where is the instantaneous velocity of the second frame Respect to the first? In this case, it is not hard to see that Equation ( 11) Just as good as another as far as Newtonian dynamics is concerned.īut, what happens if the second frame of reference accelerates with Motion is relative-hence, the name ``relativity'' for Einstein's theory. In fact, there is no absolute standard of rest: i.e., all However, Einstein showed that this is not the case. Newton through that one of these inertial frames was special, andĭefined an absolute standard of rest: i.e., a static object in this frame was in a state of absolute rest. We conclude that the second frame of reference is also an inertial frame.Ī simple extension of the above argument allows us to conclude that thereĪre an infinite number of different inertial frames moving with constant Moves in a (different) straight-line with (a different) constant speed Object is moving in a straight-line with constant speed in our original Object in the two reference frames satisfyĪccording to Equations ( 7) and ( 11), if an It is evident, from Figure 1, that at any given time,, the coordinates of the To the corresponding axes in the first frame, thatĪnd, finally, that the origins of the two frames instantaneously coincide at -see Figure 1. We can suppose that the Cartesian axes in the second frame are parallel Ĭonsider a second frame of reference moving with some With respect to the origin of the coordinate system, as a function of time. Of a point object can now be specified by giving its position vector, Set up a Cartesian coordinate system in this frame. Suppose that we have found an inertial frame of reference. Net external force moves in a straight-line with constant speed. Indeed, we can think of Newton'sįirst law as the definition of an inertial frame: i.e.,Īn inertial frame of reference is one in which a point object subject to zero However, this is only true in special frames of reference called inertial frames. In a straight-line with a constant speed ( i.e., it does not accelerate).

Newton's first law of motion essentially states that a point object Next: Newton's Second Law of Up: Newton's Laws of Motion Previous: Newton's Laws of Motion

First law of motion