x Turn on thread page Beta
 You are Here: Home >< Physics

# Inertial reference frames watch

1. From my understanding, we talk about reference frames when comparing two different objects. If two objects are either stationary or moving at constant velocity relative to the other, then we say that one is an inertial reference frame when describing the motion of the other(Is this right?).
So, if you have two identical 100m runners, that both accelerate at the same rate(and run in the same direction), then would you say one of the 100m runners is an inertial reference frame when talking about the other?
2. An Inertial Reference Frame must describe time and space (in a time independent manner) but with dimensional homogeneity (having the same units of measurements on both sides of an equation i.e. M L T) and is isotropic (has uniformity in all orientations, but no necessarily so when dealing with manifolds when isotropy has a different meaning).

Using that description then, the independent runners must each be referred to their own frame of reference.

So, both runners will have their own frame of reference which could either be the same or different.
If the frames of reference are the same, then both runners must agree with all measurements and observations

If the frames of reference are different, then the runners may not agree with mutual observations.
3. (Original post by uberteknik)
An Inertial Reference Frame must describe time and space (in a time independent manner) but with dimensional homogeneity (having the same units of measurements on both sides of an equation i.e. M L T) and is isotropic (has uniformity in all orientations, but no necessarily so when dealing with manifolds when isotropy has a different meaning).

Using that description then, the independent runners must each be referred to their own frame of reference.

So, both runners will have their own frame of reference which could either be the same or different.
If the frames of reference are the same, then both runners must agree with all measurements and observations

If the frames of reference are different, then the runners may not agree with mutual observations.
Thanks for the response, though admittedly I'm still pretty confused. I'll just have to ask one of my teachers
4. (Original post by InternetGangster)
Thanks for the response, though admittedly I'm still pretty confused. I'll just have to ask one of my teachers
You have to define what is meant by an inertial reference frame.

That is if you can measure an object to be moving in a staight line at a constant velocity or at rest when you know there are no forces acting on that object, then you are in an inertial reference frame with that object.

If you measure the body changing direction or accelerating when you know there are no forces acting on it, you are not in the same inertial reference frame, you are in different reference frames which could either be inertial or non-inertial.
5. (Original post by uberteknik)
You have to define what is meant by an inertial reference frame.

That is if you can measure an object to be moving in a staight line at a constant velocity or at rest when you know there are no forces acting on that object, then you are in an inertial reference frame with that object.

If you measure the body changing direction or accelerating when you know there are no forces acting on it, you are not in an inertial reference frame, you are in different reference frames.
Okay, I think that seemed to clear things up.
a) If, say, I am at a bowling alley, and a bowling ball is moving away from me at constant velocity, then when describing the motion of the ball, I am said to be an inertial reference frame, and the ball is said to be in an inertial reference frame. (?)
b) If that bowling ball then collides with the pins and decelerates, I am still an inertial reference frame because the deceleration can be explained using Newton's laws (?)
c) If, while the bowling ball is moving at constant velocity relative to me, a friend pushes me over, I am no longer an inertial reference frame because the acceleration of the ball cannot be explained using Newton's laws (?)
d) If, while the bowling ball is moving at constant velocity relative to me, the floor suddenly opens up and all objects including me and the bowling ball accelerate downwards with the same magnitude, then I am still an inertial reference frame (?)
6. (Original post by InternetGangster)
Okay, I think that seemed to clear things up.
a) If, say, I am at a bowling alley, and a bowling ball is moving away from me at constant velocity, then when describing the motion of the ball, I am said to be an inertial reference frame, and the ball is said to be in an inertial reference frame. (?)
b) If that bowling ball then collides with the pins and decelerates, I am still an inertial reference frame because the deceleration can be explained using Newton's laws (?)
c) If, while the bowling ball is moving at constant velocity relative to me, a friend pushes me over, I am no longer an inertial reference frame because the acceleration of the ball cannot be explained using Newton's laws (?)
d) If, while the bowling ball is moving at constant velocity relative to me, the floor suddenly opens up and all objects including me and the bowling ball accelerate downwards with the same magnitude, then I am still an inertial reference frame (?)
Be careful. A different inertial reference frame is one where only the relative motions have changed:

a), b) & d) All correct. You and the ball are measured using the SAME inertial reference frame.

c) You and the ball are in different inertial reference frames but they are nonetheless still inertial reference frames. The only thing that has changed is the relative motion between you and the ball. Newtons laws still hold true for both you and the ball.

Transformimg between the frames is simply by addition and subtraction of velocities because you and the ball agree on absolute time and space.

Non-inertial reference frames are ones where different observers cannot agree on an absolute definition of space and time.
7. Thank you for your time

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 11, 2013
Today on TSR

### Any tips for freshers...

who are introverts?

### More snow?!

Discussions on TSR

• Latest
Poll
Discussions on TSR

• Latest

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE