If I am standing in the back of a moving truck, the truck is now my frame of reference and everything will be measured compared to it. Anything that you see, watch, or measure will be compared to the reference point of the ground. In each of the above examples, we are really talking about two different people having two different frames of reference while measuring the relative velocity of one object.ДЇrame of reference: When you are standing on the ground, that is your frame of reference. My friend on the sidewalk will say that the apple is moving at ( 20m/s + -15m/s) 5m/s!.The only thing I might say that is different is that it is -15m/s, since even I should be able to notice they are going in the opposite direction now. I will still say that my apples are moving at 15m/s, because from my way of looking at it, thatвЂ™s how fast the apple is moving.Now I turn around and start throwing the apples from the rear of the truck, backwards!.

When I have thrown the apple forward, adding more velocity to it, she will say it is going at ( 20m/s + 15m/s) 35m/s!.Well, even before I throw it, sheвЂ™ll say that the apple is moving at 20m/s (the speed of everything on the truck).How fast does my friend on the sidewalk say the apple is moving?.Still 15m/s! Relative to me, I can only make an apple move away from me at 15m/s, so thatвЂ™s how fast I measure the apple moving away from me.If I am really not paying attention to whatвЂ™s going on around me (like the fact that I am standing in the back of a moving truck), how fast would I say the apples are moving?.I am still throwing apples forwards, exactly the same as I was throwing them before, at 15m/s. Now the truck starts to move forwards at 20m/s.Since she will see them exactly the same way as me ( we're both in the same reference frame), she will say 15m/s.If a person were standing on the sidewalk, how fast would she say the apples are moving?.I know that I can throw an apple at exactly 15m/s every time. In all of the following examples, ignore air resistance.Д®xample 1: LetвЂ™s say I am standing on the back of a pickup truck (that is motionless), and I am throwing apples forwards.The best way to see how this is possible is to look at some examples.This is not because one of them is wrong, but because they are using different frames of reference.Relative motion is just a way of saying that sometimes different people will say different things about the motion of the same object. This is called an inertial frame of reference. A frame of reference can be thought of as any spot your doing your measurement from as long as it is not accelerating.

Quartzcode use relative frame