This result means the second athlete is 18 m on the left of the first one after 14 seconds. Thus, if the initial position of the object is x ⃗ 0 units to the reference point and the object is moving at constant velocity v ⃗, the equation of motion which gives the position x ⃗ of the object at any instant t, is This includes the situations described in Uniform Motion explained in the previous tutorials. Case 1 - Reference frame is at rest and the object is moving at constant velocity Therefore, we say "the motion is relative its parameters may be different in two different reference frames although the rhythm of motion may be the same."įor simplicity, in this tutorial we will focus purely on one-dimensional motions as the same approach can also be used for two and three-dimensional motion as well only the mathematical apparatus becomes more complex.
Therefore, if we take the Sun as a reference point (frame), we say it the Earth that is moving, not the Sun.Īs seen in the above examples, the motion of an object does not depend only on the values of its kinematic quantities but also on the reference frame chosen to study its motion. However, we know this does not occur due to the Sun movement (which takes place in any case), but because of the Earth's rotation around its axis from West to East. If we take our actual position as a reference point (frame), we say the Sun moves from East to West.However, if we chose the reference frame any object inside our car, it seems the trees are moving in the opposite direction of ours. It is obvious for a person who is sitting under a tree, we are moving together with our car past the trees.Therefore, it depends on the reference frame chosen saying whether we are moving or not. However, for somebody who is watching us from outside the Earth, for example from a satellite, we are moving (rotating) together with the Earth. In the first question, we can say that if the actual position of our body is taken as reference frame, then we are at rest.To help readers understand this point as easier as possible, let's answer to the questions posed in the "Introduction" paragraph. The motion involved in such cases is known as "relative motion." In this tutorial, we will discuss about the relationship between the kinematic quantities when the reference point is not stationary. Hence, the approach with moveable origin is more realistic than that with stationary one. In fact, everything in the universe is moveable. So far, we have discussed situations involving motions whose kinematic quantities were measured starting from a fixed location known as "reference point (frame)" or "origin." It means the origin was presumed as unmoveable.īut happens if the origin is not stationary? It is obvious the values of kinematic quantities will not be the same as if origin was stationary. Does the Sun really move or maybe something else happens instead? Explain your opinion. When you look the Sun, it does not seem to be at the same position it was one or two hours ago. Are the trees really moving? Explain your opinion again.ģ. The sideways trees look moving in the opposite direction of you. Do you think you are completely at rest or you are moving in any way? Explain your opinion.Ģ.
How to calculate the position of objects in different situations during a relative motion?ġ.
How do the kinematic quantities change during the relative motion?.How does the movement of reference frame affects the motion of an object?.Immediately we spot that the final velocity, $v$ and the time, $t$ are not in SI units.In this Physics tutorial, you will learn: