Relative velocity of river swimmer

In summary, the conversation discusses the concept of velocity in still water in the context of swimmer-river physics problems. The question is whether the velocity should be considered with respect to the ground or with respect to the river. It is explained that in still water, both choices are correct. However, if there is a current, it is important to specify the reference point. The idea of relative velocity is also mentioned, and it is suggested to think of absolute motion as a combination of relative motion and dragging motion. Finally, it is recommended to consult a physics textbook or teacher for a better understanding of the concept.
  • #1
gracy
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in swimmer-river physics problems ,velocity of swimmer in still water=velocity of swimmer with respect to ground OR velocity of swimmer in still water=velocity of swimmer with respect to river
which of these is correct .I am really confused.
 
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  • #2
I don't know anything about swimming. In flying, a pilot uses "ground speed" for navigation and "airspeed" for performance characteristics. They're related and both are necessary. I would expect swimming to be similar, since fluid dynamics rules both situations.
 
  • #3
Danger said:
I don't know anything about swimming. In flying, a pilot uses "ground speed" for navigation and "airspeed" for performance characteristics. They're related and both are necessary. I would expect swimming to be similar, since fluid dynamics rules both situations.
i am talking in context of swimmer-river physics numericals.
 
  • #4
Sorry... I just re-read your first post more carefully. In still water, there is no difference between the river and the ground as reference points, so both of your choices are correct.
 
  • #5
gracy said:
in swimmer-river physics problems ,velocity of swimmer in still water=velocity of swimmer with respect to ground OR velocity of swimmer in still water=velocity of swimmer with respect to river
which of these is correct .I am really confused.

In still water, they're the same so are both equally correct. If there's a current, then the problem is incompletely specified if it doesn't say which one is intended.

In some problems, you will be expected to figure out which one is intended from the context.
 
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  • #6
There is no problem if you use the velocity through the water vector and the velocity of the water vector. The velocity over the ground is the vector sum. How is that confusing? Vectors work that way and sticking to the rules will give the right answer. (As long as we avoid relativistic situations or different geometries)
 
  • #7
I have done so many problems like these (river-boat). I have done those from I E IRODOV and S S KROTOV. There I took velocity in still water as velocity wrt river.
Reason : if I am the river, to me I am at rest. To earth, I am flowing. Hence to me the boat moves with the velocity the sailor thinks he is moving...
I have got all answers using this. I was confused initially.IF U HAVE A SPECIFIC QUESTION, I CAN SHOW YOU HOW TO USE RELATIVE VELOCITY CONCEPT.
 
  • #8
AdityaDev said:
I have done so many problems like these (river-boat). I have done those from I E IRODOV and S S KROTOV. There I took velocity in still water as velocity wrt river.
Reason : if I am the river, to me I am at rest. To earth, I am flowing. Hence to me the boat moves with the velocity the sailor thinks he is moving...
I have got all answers using this. I was confused initially.IF U HAVE A SPECIFIC QUESTION, I CAN SHOW YOU HOW TO USE RELATIVE VELOCITY CONCEPT.
you are right in my textbook also velocity in still water is taken as velocity wrt river.But i am still not getting it' reason.
 
  • #9
gracy said:
you are right in my textbook also velocity in still water is taken as velocity wrt river.But i am still not getting it' reason.
I guess "velocity In still water" is short for "velocity in the reference frame where the water is at rest", or for "velocity in the ground frame if the water wouldn't move relative to the ground".
 
  • #10
Always remember the simple rule that absolute motion is relative motion plus dragging motion, where:

Absolute motion => that of the swimmer with respect to the river's bank
Relative motion => that of the swimmer with respect to the water
Dragging motion => that of the water with respect to the river's bank

With that in mind, solving that type of problems becomes very easy.
 
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  • #11
gracy said:
you are right in my textbook also velocity in still water is taken as velocity wrt river.But i am still not getting it' reason.
1)Imagine you are the river.to you, you are at rest.
2)Now velocity in still water means that the water is not flowing. The possibilities are that it can be with respect to ground or wrt river.
3) If I am the ground, I can see the river flowing.Hence it is not wrt ground.
4)If I am the river I feel that I am at rest. It is like traveling in a train on a very smooth track. You can't feel the train moving unless you look out of the window.Hence it has to be wrt river.
5) If you still don't understand ask your physics teacher or refer " Halliday Resnick and Krane" book or any mechanics book by reputed authors.
 

1. What is the relative velocity of a river swimmer?

The relative velocity of a river swimmer refers to the speed and direction at which the swimmer is moving in relation to the current of the river. It takes into account both the swimmer's own velocity and the velocity of the river's current.

2. How is the relative velocity of a river swimmer calculated?

The relative velocity of a river swimmer can be calculated using vector addition. The swimmer's own velocity vector is added to the velocity vector of the river's current, resulting in the relative velocity vector of the swimmer.

3. Does the relative velocity of a river swimmer affect their speed?

Yes, the relative velocity of a river swimmer can either increase or decrease their speed depending on the direction and magnitude of the current. If the current is moving in the same direction as the swimmer, their speed will increase. If the current is moving in the opposite direction, their speed will decrease.

4. Can the relative velocity of a river swimmer be changed?

Yes, the relative velocity of a river swimmer can be changed by altering either their own velocity or the velocity of the river's current. The swimmer can adjust their own speed and direction by changing their stroke technique, while the current's velocity can be affected by factors such as water depth and obstacles.

5. Why is understanding the relative velocity of a river swimmer important?

Understanding the relative velocity of a river swimmer is important because it can help the swimmer navigate the river more effectively and efficiently. By taking into account the current's velocity, the swimmer can choose the most efficient path and conserve energy. It is also important for safety, as the current's velocity can pose a risk to swimmers if not accounted for.

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