12/7/2023 0 Comments Harbor freight air compressor![]() Say a boat is moving to the north at 4m/s on a river. This can be stretched to as many entities/observers/reference frames as you want. NOTE: If instead of three (as in this example), there are four entities involved, we can simply calculate the relative velocities as So to find the velocity of the cat with respect to the ground observer, we need to add the velocity of the cat with respect to the train and the velocity of the train with respect to the ground observer. Then we calculate relative velocity of the cat with respect to the ground observer as The velocity of the train with respect to ground observer is The velocity of the cat with respect to ground observer is The velocity of the cat with respect to the train is The the cat is also walking away on the train towards the east. Lets say the train is moving towards the east. Now let us go back to our very first example with the cat, the train and an observer on the ground. This concept of moving co-ordinate system will play an important part in understanding Einsten’s Theory of Relativity So for car-B, car-A is moving towards the right with 50m/s ![]() So car-B will see car-A moving towards car-B at 50m/s. You will also notice that since the co-ordinate system moves along with car-B, its own position never changes on this co-ordinate system! So we see the co-ordinate system of car-B moves with it when car-B moves to the left, and thus the position of car-A on this co-ordinate system changes from point-p1 to point-p2! Remember that observers are always at rest in their own reference frame. to the left.Īs we can see the picture, the position of car-B changes as it moves to the left on the co-ordinate system of car-A.īut, what if we take car-B to be the observer? Now if we take car-A to be the observer, then car-B will be moving at 50m/s towards car -A, i.e. Ĭar-A is stationary but car-B is moving at a constant velocity of 50m/s to the left towards car-A according to an observer on the ground. Car-A (at the leftmost end) and car-B(at the rightmost end). Lets take an example to understand relative motion. Remember the reference frame can be considered a co-ordinate system that is moving along with the observer! Whenever we talk about motion in physics, it is always relative to an observer or a frame of reference.Īn observer is always stationary in his/her own reference frame and everything else moves or is at rest with respect to this reference frame. Relative Motionįor the reasons we have discussed this far, we never talk about absolute motion. You will not be able to notice any difference and if all the windows are closed, you won’t be able to tell if the plane is flying or is stationary just by observing the motion of the basketball. Now say you are on the plane and it is flying very smoothly (without any turbulence) and you again dribble the basketball. But these make so little difference most of the time, that for present purposes we will consider it as an inertial, non-accelerating frame of reference.Īnother important point to note is that it is impossible to figure out whether motion of an object is being observed from a stationary reference frame or a frame moving in constant velocity, by just observing the motion of the object.įor example, say a plane is stationary on the ground without any movement and you dribble a basketball inside the plane. *technically earth in not inertial since it is rotating around its axis, revolving around the sun, etc. Since most of the motion we are concerned with takes place on the surface of our planet, earth is the most common reference frame. The laws of physics observed from all inertial reference frames are same. It moves in the same manner as the observer.Ī reference frame describe the motion of an observer.įor the time being we will deal with only reference frames which are inertial, which means they are non-accelerating. ![]() What is a Reference Frame?Ī reference frame is the co-ordinate system that the observer uses to measure motion. This is where the concept of Reative Motion arises. Thus the motion is always relative to the reference frame of an observer. So for you this cat is stationary.īut if a person from outside the train observes, he or she will see this cat moving away at the same speed – ‘v’as the train! Lets say a cat is sitting on a chair in front of you. Say you are on a train, which is moving with a constant velocity – ‘v’. ![]() If two observers are moving different manners, they might observe the same event in differently. In Physics, motion is always described from the point of view of an observer. ![]()
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