Why is it so important to have a frame of reference when measuring motion?

Why is it so important to have a frame of reference when measuring motion?



what are the differences between, speed; velocity; average speed; and instantaneous speed.



What do they all have in common?



Frame of reference is pretty confusing. if anyone can help that'd be great!Why is it so important to have a frame of reference when measuring motion?frame of reference is important because if you are floating in space and their is nothing else you have no way to tell where you are, you can only define motion relative to another object.

velocity has a direction but speed does not. average speed is the change in position divided by change in time, instantaneous speed is the absolute value of the derivative of position.

they are all rates of change in positionWhy is it so important to have a frame of reference when measuring motion?because without a reference it's difficult to sense the motion. For example we are traveling with the Earth at a very high speed revolving the sun but if we use Earth as the frame of reference we are still without motion at all.



Speed is directionless and is a generic term for distance traveled within a certain period of time. It's called a scalar (only magnitude without direction)

velocity has direction so it's called a vector (opposed to scalar, a vector has both length or magnitude and direction)

average speed is the distance traveled within a period of time divided by time

instantaneous speed is the average speed over a tiny period of time (unless you know the concept of limit)Why is it so important to have a frame of reference when measuring motion?Alright...thought experiment time:

You are riding a train. You've just woken up after a sleep that lasted several hours. The train could've gone thorugh numerous coupling/de-coupling cycles, so any reference you initially made at the time of boarding is meaningless. All curtains are closed over the windows and all windows themselves are closed. Your train cabin is completely isolated, nowhere does it tell you which way front and back are.

You can tell the train is moving? How? BUT, can you tell which direction? (Hint: no)
How can you tell when the train is accelerating (in the full physics form of the word)?

Is there any experiment you can do entirely within the train cabin to measure its speed?


And finally, since there isn't, what reference frame are you ultimately forced to use for all your kinematics measurements?


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With that in mind, we define a reference frame as: an "imaginary black box" that is used to define our immediate environment, and from which we use as the basis of all kinematics measurements. I.e. the reference frame itself defines as stationary, all motion is measured relative to it.