# The Naked Scientists Forum

### Author Topic: How do two separate atomic clocks measure the velocity of two falling particles?  (Read 918 times)

#### Thebox

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##### How do two separate atomic clocks measure the velocity of two falling particles?
« on: 11/04/2016 08:00:46 »
If we have two identical objects, that are falling at the same speed and hitting the ground simultaneously, and we were to record the time is takes for them to fall on two different atomic clocks,

Clock 1 in the inertia reference frame,

Clock 2 in dilation on an aeroplane,

Hows does that work ?

Does the objects slow down for one clock because time slows down?

I woke up confused, sorry for so many questions.

« Last Edit: 11/04/2016 09:00:50 by chris »

#### evan_au

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##### Re: How do two separate atomic clocks measure the velocity of two falling particles?
« Reply #1 on: 11/04/2016 11:33:55 »
Quote from: TheBox
Clock 1 in the inertia reference frame
There is not a single "inertial" reference frame, there are many. And Einstein suggested that any inertial frame is just as valid as any other inertial frame.

If you take two observers in two different inertial frames, they may disagree about how long things took, or in what order they occurred, if they occurred in different places. So some observers may see the two objects being dropped at the same instant, while others with think one (or the other) dropped first. Similarly, some observers will think that one (or the other) hit the ground first.

So the observers will not know when to start and stop their clocks.

This is the problem of simultaneity, see: https://en.wikipedia.org/wiki/Relativity_of_simultaneity

Note: As I understand it, someone standing on the ground is not in an inertial frame of reference, because the ground is pushing up on their feet and/or seat.

Quote
Clock 2 in dilation on an aeroplane
How do you know that the clock on the plane will be running slowly?
• It is true that a clock traveling quickly at ground level will seem to be running more slowly.
• But planes normally travel very high, so they are farther out of Earth's gravitational field, so the clock in the plane should run faster than the clock on the ground.
• Whether the clock on the plane is running faster or slower than one on the ground depends on what speed, and at what altitude.

• Someone on the ground, near the dropping balls will see the clock on the fast plane running slow.
• Someone on the fast plane, looking at the person on the ground will see the clock on the ground running slow.
Which clock is really running slow?

Einstein says it doesn't matter. Time is all relative anyway. Get over it.

#### Thebox

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##### Re: How do two separate atomic clocks measure the velocity of two falling particles?
« Reply #2 on: 11/04/2016 13:33:03 »
Quote from: TheBox
Clock 1 in the inertia reference frame
There is not a single "inertial" reference frame, there are many. And Einstein suggested that any inertial frame is just as valid as any other inertial frame.

If you take two observers in two different inertial frames, they may disagree about how long things took, or in what order they occurred, if they occurred in different places. So some observers may see the two objects being dropped at the same instant, while others with think one (or the other) dropped first. Similarly, some observers will think that one (or the other) hit the ground first.

So the observers will not know when to start and stop their clocks.

This is the problem of simultaneity, see: https://en.wikipedia.org/wiki/Relativity_of_simultaneity

Note: As I understand it, someone standing on the ground is not in an inertial frame of reference, because the ground is pushing up on their feet and/or seat.

Quote
Clock 2 in dilation on an aeroplane
How do you know that the clock on the plane will be running slowly?
• It is true that a clock traveling quickly at ground level will seem to be running more slowly.
• But planes normally travel very high, so they are farther out of Earth's gravitational field, so the clock in the plane should run faster than the clock on the ground.
• Whether the clock on the plane is running faster or slower than one on the ground depends on what speed, and at what altitude.

• Someone on the ground, near the dropping balls will see the clock on the fast plane running slow.
• Someone on the fast plane, looking at the person on the ground will see the clock on the ground running slow.
Which clock is really running slow?

Einstein says it doesn't matter. Time is all relative anyway. Get over it.

While I associate myself with the twins paradox , can you please explain how the ground is able to apply opposite direction to gravity and push back according to Newtons third law?

The ground is clearly travelling the same direction has the object and it is surely the object imposes a force on the ground and gravity imposes a force on the ground.  The ground is not capable of pushing back it is only capable of density which is the resistance to ''falling'',  when are we ever not falling?

#### Thebox

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##### Re: How do two separate atomic clocks measure the velocity of two falling particles?
« Reply #3 on: 11/04/2016 13:37:07 »

The twin leaves earth at 0t  ,  he returns at 0t ,  why he was gone they were counting, none of them managed to count at the same rate causing an imaginary age difference. They aged the same but the numbers showed a different because they did not have a constant counting system.

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#### Colin2B

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##### Re: How do two separate atomic clocks measure the velocity of two falling particles?
« Reply #4 on: 11/04/2016 14:27:00 »
causing an imaginary age difference. They aged the same ......
Experimental evidence shows otherwise.

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#### Thebox

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##### Re: How do two separate atomic clocks measure the velocity of two falling particles?
« Reply #5 on: 11/04/2016 14:40:37 »

Experimental evidence shows otherwise.

What experimental evidence related to time shows this to be true then?

#### evan_au

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##### Re: How do two separate atomic clocks measure the velocity of two falling particles?
« Reply #6 on: 11/04/2016 22:24:53 »
Quote from: TheBox
when are we ever not falling?
When we are asleep on our beds. We have to wake up every so often and turn over to get comfortable, because the bed is pushing up on us.

Astronauts on the ISS are falling. You can tell because they are in microgravity.

#### Thebox

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##### Re: How do two separate atomic clocks measure the velocity of two falling particles?
« Reply #7 on: 11/04/2016 22:28:03 »
Quote from: TheBox
when are we ever not falling?
When we are asleep on our beds. We have to wake up every so often and turn over to get comfortable, because the bed is pushing up on us.

Astronauts on the ISS are falling. You can tell because they are in microgravity.

When we are asleep in our beds, the bed and us want to fall through the ceiling.

I fail to see how you have answered the question about falling..   An object in an inertia reference frame experiences Newtons of force while at rest mass, the object is still trying to fall is it not?

We are still accelerating at 9.81m/s but not moving is that not so?

#### The Naked Scientists Forum

##### Re: How do two separate atomic clocks measure the velocity of two falling particles?
« Reply #7 on: 11/04/2016 22:28:03 »