Relative Motion: Visceral Reminder of Its Meaning

In summary: Amtrak ride, especially an express train, it feels like the train is moving even when it's really just standing still.In summary, this person experienced a disorienting and anxiety-provoking situation where they thought their car was moving backwards.
  • #1
phinds
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I spend a lot of time here helping newbies understand that it simply is not meaningful to talk about motion without any reference what it is that the motion is relative to.

Today, I had THE most visceral reminder of that that I think I've ever had. My car's idle has somehow gone to being set way too high and I'm going to get into the mechanic soon, but meanwhile, I'm very aware of the vigorous running of the engine when I park and before I turn the car off.

In the grocery store parking lot I pulled through a space such that my car's front was facing the aisle and the cars on both sides of me had their trunks facing that aisle.

I parked and RIGHT as I put the car into park, I was fairly sure, the car next to me started backing out and I was so convince that MY car was moving backwards, due to my having inadvertently put the car in reverse that my stomach lurched and I pressed the brake petal so hard I damned near broke my foot.

It was a sheer panic reaction and of course would have been the right thing to do had I actually been moving. But I wasn't(*) o:)

* relative to the ground, which is what counted.
 
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  • #2
phinds said:
I spend a lot of time here helping newbies understand that it simply is not meaningful to talk about motion without any reference what it is that the motion is relative to.

Today, I had THE most visceral reminder of that that I think I've ever had. My car's idle has somehow gone to being set way too high and I'm going to get into the mechanic soon, but meanwhile, I'm very aware of the vigorous running of the engine when I park and before I turn the car off.

In the grocery store parking lot I pulled through a space such that my car's front was facing the aisle and the cars on both sides of me had their trunks facing that aisle.

I parked and RIGHT as I put the car into park, I was fairly sure, the car next to me started backing out and I was so convince that MY car was moving backwards, due to my having inadvertently put the car in reverse that my stomach lurched and I pressed the brake petal so hard I damned near broke my foot.

It was a sheer panic reaction and of course would have been the right thing to do had I actually been moving. But I wasn't(*) o:)

* relative to the ground, which is what counted.
I don't want to imagine what would've happened if during that moment your foot had hit the accelerator instead :nb)
Btw, shouldn't this go in the general discussion forum? (unless of course you want to discuss the scientific aspect of your experience)
 
  • #3
phinds said:
I parked and RIGHT as I put the car into park, I was fairly sure, the car next to me started backing out and I was so convince that MY car was moving backwards, due to my having inadvertently put the car in reverse that my stomach lurched and I pressed the brake petal so hard I damned near broke my foot.

I've had this happen 3 times myself. It's really disconcerting. That disconnect between I'm slamming on the brake as hard as I can, but the car is still moving is freaky.
Kinda glad to hear that I'm not the only one that this has happened to.
 
  • #4
Similar confusions are a common occurrence when several people are moving small boats at the same time in a crowded anchorage. At anchorage speeds there's no tactile cue from the motion of wind and water.
 
  • #5
Nugatory said:
Similar confusions are a common occurrence when several people are moving small boats at the same time in a crowded anchorage. At anchorage speeds there's no tactile cue from the motion of wind and water.
Oh, yeah, now that you remind me I had a similar experience on a sailboat a LONG time ago, but that wasn't a panic situation because I wasn't driving and it wasn't my boat, so I just grabbed something and then looked sheepish.
 
  • #6
PWiz said:
I don't want to imagine what would've happened if during that moment your foot had hit the accelerator instead :nb)
GADS ... I hadn't even thought of that.
Btw, shouldn't this go in the general discussion forum? (unless of course you want to discuss the scientific aspect of your experience)
That's where I started to put it but I don't seem to be navigating well, because all I saw were 5 or 6 specific sub forums and it clearly didn't seem to belong in any of them.
 
  • #7
It's a classic with trains. It doesn't happen with the dinky commuter trains because the motors are right under your feet and you can hear them start. But train sets with separate electric power cars are different - I've had a few "this train shouldn't be going yet, am I on the wrong one" moments before realising either it's the train at the next platform pulling out or the station's pulling out with us.

Side question, since phinds mentioned the concept: we typically say that there are no special or priviledged frames in SR, meaning that none is picked out by the laws of physics. But there are usually one or two frames picked out by the scenario - the local Earth's surface rest frame being a case in point. Does anyone know if there is an "official" term for these?
 
  • #8
Ibix said:
Side question, since phinds mentioned the concept: we typically say that there are no special or priviledged frames in SR, meaning that none is picked out by the laws of physics. But there are usually one or two frames picked out by the scenario - the local Earth's surface rest frame being a case in point. Does anyone know if there is an "official" term for these?

Convenient frame!
 
  • #9
Ibix said:
Does anyone know if there is an "official" term for these?
That's probably the 'Me' frame and the 'My ex' frame. We ended up drifting apart at a considerable fraction of c. I couldn't stand her obsession with time dilation, and she saw me as too much length contracted.
 
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  • #10
I think it would be great if you wrote an Insight article about this. Then, rather than having to answer each new thread with lots of dialogue, you can simply give a link to the Insight article.

Last week, I was driving on a straight flat section of the Jersey Turnpike, and tried to imagine that the car was standing still and all the scenery was moving by backwards. It was quite a weird feeling.

Chet
 
  • #11
Chestermiller said:
I think it would be great if you wrote an Insight article about this. Then, rather than having to answer each new thread with lots of dialogue, you can simply give a link to the Insight article.

Last week, I was driving on a straight flat section of the Jersey Turnpike, and tried to imagine that the car was standing still and all the scenery was moving by backwards. It was quite a weird feeling.

Chet

Along those same lines, I remember reading that something some astronauts have really enjoyed as part of being out on a spacewalk is this:

No wind, no environmental sounds, nothing, just floating in their suits in an EVA orbiting the Earth, it's very easy for them to forget that they're orbiting and to start thinking of themselves as floating still with the Earth spinning silently underneath them.

I can't help but imagine that must be a really amazing, profound feeling.

Here's a beautiful video that I think captures it really well:


Of course, what we're all talking about is how it's impossible to define absolute motion in a physical sense. Here, though, it's very difficult to decide whether the camera's orbiting the Earth or the Earth is spinning underneath in an (untrained) intuitive sense, too, though.
 
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Related to Relative Motion: Visceral Reminder of Its Meaning

1. What is relative motion?

Relative motion is the movement of an object in relation to another object. It is the change in position of an object with respect to a reference point or frame of reference.

2. How is relative motion different from absolute motion?

Absolute motion is the movement of an object with respect to a fixed reference point, while relative motion is the movement of an object with respect to another moving object. In relative motion, the reference point is constantly changing, making it a more complex concept to understand.

3. What is the significance of relative motion in everyday life?

Relative motion is an important concept in understanding the movement of objects in our daily lives. It helps us understand how objects move in relation to each other, and how our observations may change depending on our reference point. It is also crucial in fields such as physics, engineering, and astronomy.

4. How does the concept of relative motion apply to bodies in motion?

In the study of bodies in motion, relative motion is used to analyze the movement and interactions of different objects. It helps determine the velocity, acceleration, and direction of an object in relation to another object. This is important in understanding how forces and motion affect the behavior of bodies in motion.

5. Can you give an example of relative motion?

One example of relative motion is when two cars are traveling at different speeds on the same highway. To a passenger in one car, the other car may appear to be moving backwards or forwards, depending on its speed and direction. This is because the reference point is constantly changing as both cars are in motion.

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