Relative speed when someone runs on the treadmill

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Discussion Overview

The discussion revolves around the concept of relative speed in the context of a person running on a treadmill while using VR technology. Participants explore how the speeds of the person and the treadmill interact, particularly when viewed by an observer. The scope includes theoretical considerations and practical implications for a study involving individuals with spinal cord injuries.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants question how the running speed of a person can differ from the treadmill speed, suggesting that a diagram might clarify the scenario.
  • One participant notes that if the speeds are much smaller than the speed of light, they can be added normally.
  • Another participant raises concerns about the implications of differing speeds, suggesting that a person could fall off the treadmill if their speed does not match the treadmill's.
  • Several participants discuss the mechanics of speed addition or subtraction depending on the direction of movement, using analogies such as moving walkways to illustrate their points.
  • One participant emphasizes that the speed of the person relative to the ground is fixed by a harness, implying that the treadmill speed must match to prevent injury.
  • A later reply questions the rationale for updating the VR view based on what an observer sees rather than the runner's perspective.
  • Another participant clarifies that if person A runs at 5 m/s relative to the treadmill and the treadmill runs at 7 m/s, person B would see person A moving backwards at 2 m/s.
  • Concerns are raised about the need for the treadmill speed to match the runner's speed to maintain safety and proper functioning of the VR system.

Areas of Agreement / Disagreement

Participants express confusion and differing views regarding the relationship between the speeds of the person and the treadmill. There is no consensus on how to approach the problem, and multiple competing interpretations of the scenario remain present.

Contextual Notes

Participants highlight the importance of visual aids, such as diagrams, to clarify the scenario. There are unresolved assumptions regarding the fixed nature of the runner's speed and the implications of speed differences on safety.

canucks
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We are using VR technology for people with spinal cord injury ( incomplete so they can walk with assistance) for a study. They will be walking on a treadmill wearing an oculus. We have a question regarding relative speed since we are updating the software view based on that
if person A runs at 5 m/s , treadmill runs at 7 m/s , opposite direction of the person . If person B is watching, at what speed do they appear..aka what's the relative speed? what if treadmill and peron run in the same direction as person A . What speed does person B see him?
 
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I'm confused: how can the running and treadmill speeds be different? A diagram might help...
 
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russ_watters said:
I'm confused: how can the running and treadmill speeds be different? A diagram might help...
Imagine if you running really fast on the treadmill or grabbing on the parallel bar and walking slowly.
 
Assuming that speeds involved are much smaller than the speed of light in vacuum, they just add normally.

russ_watters said:
I'm confused: how can the running and treadmill speeds be different? A diagram might help...
The person could change position relative to the treadmill? Of course, this would eventually lead to the person falling off the treadmill...
 
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canucks said:
Imagine if you running really fast on the treadmill or grabbing on the parallel bar and walking slowly.
This doesn't help. If my speed and the treadmill speed don't match, don't I fall off?
 
We are using Lokomat treadmill so he is wearing a harness and won't fall. Are we adding or deducting the speeds if they move on the same direction?
 
Orodruin said:
The person could change position relative to the treadmill? Of course, this would eventually lead to the person falling off the treadmill...
Yes, though I don't think I'd use the word "eventually" to describe a half second...
 
russ_watters said:
Yes, though I don't think I'd use the word "eventually" to describe a half second...
Depends on the size of the treadmill ;)
 
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  • #10
canucks said:
We are using Lokomat treadmill so he is wearing a harness and won't fall. Are we adding or deducting the speeds if they move on the same direction?
Sorry, I can't help you until you fully describe the scenario. A diagram is highly recommended.
 
  • #11
Orodruin said:
Depends on the size of the treadmill ;)
Agreed.
 
  • #12
canucks said:
We are using Lokomat treadmill so he is wearing a harness and won't fall. Are we adding or deducting the speeds if they move on the same direction?
Think about it this way - if you are walking on one of those travellator moving walkways, you do it to go faster, right? Does the belt move towards your destination or away from it?
 
  • #13
canucks said:
We are using Lokomat treadmill so he is wearing a harness and won't fall. Are we adding or deducting the speeds if they move on the same direction?

If someone is on a moving walkway at the airport and that is going at, say, 2m/s. And you watch them, then they are going at 2m/s relative to you.

If they start to walk at 1m/s relative to the walkway then you see them move at 3m/s.

If they walk at 1m/s "the wrong way" on the walkway, then you see them move at 1m/s.

Isn't that all rather obvious?
 
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  • #14
I think it is not so relevant to the OPs question though. It seems the speed of the person relative to the ground is fixed by a harness so the treadmill speed needs to be exactly opposite to the treadmill speed or the person will likely get injured.
 
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  • #15
Orodruin said:
treadmill speed needs to be exactly opposite to the treadmill speed
That is often accomplished with poured concrete. :-)
 
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  • #16
jbriggs444 said:
That is often accomplished with poured concrete. :-)
Oops. Meant to have one of those as the walking speed ...
 
  • #17
canucks said:
We are using VR technology for people with spinal cord injury ( incomplete so they can walk with assistance) for a study. They will be walking on a treadmill wearing an oculus. We have a question regarding relative speed since we are updating the software view based on that
if person A runs at 5 m/s , treadmill runs at 7 m/s , opposite direction of the person . If person B is watching, at what speed do they appear..aka what's the relative speed? what if treadmill and peron run in the same direction as person A . What speed does person B see him?

Why are you updating the VR view based on what some person B sees, and not on what A would see running at 5 m/s?
 
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  • #18
canucks said:
if person A runs at 5 m/s , treadmill runs at 7 m/s , opposite direction of the person . If person B is watching, at what speed do they appear..aka what's the relative speed?

So person A runs at 5 m/s relative to the treadmill belt.
Treadmill runs at 7 m/s relative to the ground the treadmill machine is standing on.

If person B is standing on the ground then it appear to him that Person A is moving backwards at 2m/s.

If the treadmill machine is say 2m long he will fall off the back of the treadmill in 1 second unless he runs faster.

If he is lightly suspended in a harness that attempts to fix his position relative to the ground his feet will be swept out from under him unless he runs faster (eg at the same speed as the belt).

I believe you need to match the speed of the belt to the runner and show the VR at the same speed.
 

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