Difference between relative velocity and effective velocity

In summary: Relative to the guy (or the boat), the rock has velocity vrg. Relative to the water, it has velocity vrg+vbw. Relative to the shore, it has velocity vrg+vbw+vws. Relative to the center of the Earth, it has velocity vrg+vbw+vws+vsc, where the last term is the speed of the surface relative to the center of the Earth. You can similarly calculate the velocity of the rock relative to the Sun, relative to the Milky Way, or relative to a galaxy far far away. All velocities are relative velocities and it is important to be clear about what they are relative to.As for effective velocity, it is a concept
  • #1
Abhimessi10
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Can anyone tell me the difference between concept of relative velocity and effective velocity and when to use the concept of relative velocity?

For example, if a guy throws a ball from a moving object at an angle theta it undergoes projectile motion we write horizontal velocity as ucostheta+v(effective velocity)why not ucostheta-v(relative velocity)
 
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  • #2
First you decide what reference frame to use, then you consider the velocity relative to the chosen frame. As long as you are consistent and refer all velocities to the chosen frame, you are OK. For example, suppose the guy is standing on a boat in a river moving with speed vbw relative to the water and the water is moving with speed vws relative to the shore. Now if the guy throws a rock and he sees it move away from him with speed vrg, there many velocities that the rock has depending on the frame in which yo want to express it.
Relative to the guy (or the boat), the rock has velocity vrg.
Relative to the water, it has velocity vrg+vbw.
Relative to the shore, it has velocity vrg+vbw+vws.
Relative to the center of the Earth, it has velocity vrg+vbw+vws+vsc, where the last term is the speed of the surface relative to the center of the Earth.
You can similarly calculate the velocity of the rock relative to the Sun, relative to the Milky Way or relative to a Galaxy far far away. You see how it goes. All velocities are relative velocities and you need to be clear what they are relative to, i.e. the frame of reference you have chosen to express them in.

As far as effective velocity is concerned, I didn't know what it was and looked it up. I found this link
http://probaseballinsider.com/effective-velocity-what-is-it-how-is-it-used-how-can-it-help-pitchers/
where it is stated that effective velocity (in baseball) is a combination of two things, (a) A hitters perceived velocity and (b) How far a hitter has to move his bat to make contact. In my opinion this definition is a statistical concept that may be useful in baseball but not in physics because item (a) is subjective and depends on the hitter while item (b) is an attempt to define this velocity as distance-dependent which adds to the fuzziness of the concept.
 
  • #3
You need to define ##u## and ##v## here.
 
  • #4
So
kuruman said:
First you decide what reference frame to use, then you consider the velocity relative to the chosen frame. As long as you are consistent and refer all velocities to the chosen frame, you are OK. For example, suppose the guy is standing on a boat in a river moving with speed vbw relative to the water and the water is moving with speed vws relative to the shore. Now if the guy throws a rock and he sees it move away from him with speed vrg, there many velocities that the rock has depending on the frame in which yo want to express it.
Relative to the guy (or the boat), the rock has velocity vrg.
Relative to the water, it has velocity vrg+vbw.
Relative to the shore, it has velocity vrg+vbw+vws.
Relative to the center of the Earth, it has velocity vrg+vbw+vws+vsc, where the last term is the speed of the surface relative to the center of the Earth.
You can similarly calculate the velocity of the rock relative to the Sun, relative to the Milky Way or relative to a Galaxy far far away. You see how it goes. All velocities are relative velocities and you need to be clear what they are relative to, i.e. the frame of reference you have chosen to express them in.

As far as effective velocity is concerned, I didn't know what it was and looked it up. I found this link
http://probaseballinsider.com/effective-velocity-what-is-it-how-is-it-used-how-can-it-help-pitchers/
where it is stated that effective velocity (in baseball) is a combination of two things, (a) A hitters perceived velocity and (b) How far a hitter has to move his bat to make contact. In my opinion this definition is a statistical concept that may be useful in baseball but not in physics because item (a) is subjective and depends on the hitter while item (b) is an attempt to define this velocity as distance-dependent which adds to the fuzziness of the concept.[/QUOT
kuruman said:
First you decide what reference frame to use, then you consider the velocity relative to the chosen frame. As long as you are consistent and refer all velocities to the chosen frame, you are OK. For example, suppose the guy is standing on a boat in a river moving with speed vbw relative to the water and the water is moving with speed vws relative to the shore. Now if the guy throws a rock and he sees it move away from him with speed vrg, there many velocities that the rock has depending on the frame in which yo want to express it.
Relative to the guy (or the boat), the rock has velocity vrg.
Relative to the water, it has velocity vrg+vbw.
Relative to the shore, it has velocity vrg+vbw+vws.
Relative to the center of the Earth, it has velocity vrg+vbw+vws+vsc, where the last term is the speed of the surface relative to the center of the Earth.
You can similarly calculate the velocity of the rock relative to the Sun, relative to the Milky Way or relative to a Galaxy far far away. You see how it goes. All velocities are relative velocities and you need to be clear what they are relative to, i.e. the frame of reference you have chosen to express them in.

As far as effective velocity is concerned, I didn't know what it was and looked it up. I found this link
http://probaseballinsider.com/effective-velocity-what-is-it-how-is-it-used-how-can-it-help-pitchers/
where it is stated that effective velocity (in baseball) is a combination of two things, (a) A hitters perceived velocity and (b) How far a hitter has to move his bat to make contact. In my opinion this definition is a statistical concept that may be useful in baseball but not in physics because item (a) is subjective and depends on the hitter while item (b) is an attempt to define this velocity as distance-dependent which adds to the fuzziness of the concept.
However you haven't cleared my doubt about the example that I have given.
 
  • #5
As @PeroK remarked you need to define ##u## and ##v##. They represent velocities relative to what? Also, how do you understand "effective velocity"? If your problem is with signs, i.e. when one uses plus as opposed to minus, remember that velocity is a vector and can be positive or negative. If the boat is moving to the right (positive) relative to the water and the guy throws the rock forward (also positive), then the velocity of the rock relative to the water will be vrw = vrg+vbw. If the guy throws the ball backwards (negative) then vrw = -vrg+vbw.
 
  • #6
kuruman said:
As @PeroK remarked you need to define ##u## and ##v##. They represent velocities relative to what? Also, how do you understand "effective velocity"? If your problem is with signs, i.e. when one uses plus as opposed to minus, remember that velocity is a vector and can be positive or negative. If the boat is moving to the right (positive) relative to the water and the guy throws the rock forward (also positive), then the velocity of the rock relative to the water will be vrw = vrg+vbw. If the guy throws the ball backwards (negative) then vrw = -vrg+vbw.
By effective velocity I mean resultant velocity
After I saw some videos I think that effective velocity is just another case of relative velocity which would depend on the frame of reference as you said
 
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  • #7
Abhimessi10 said:
By effective velocity I mean resultant velocity
OK, I see. Exactly what velocity you mean would be clearer if you stopped using the word "effective" or "resultant" and started using words or subscripts that clearly specify the frame of reference to which your velocity is referred as I did in post #2.
 
  • #8
Abhimessi10 said:
By effective velocity I mean resultant velocity
Abhimessi10 said:
By effective velocity I mean resultant velocity
After I saw some videos I think that effective velocity is just another case of relative velocity which would depend on the frame of reference as you said
If you don't mind you I could give the link to
the question (video)
 
  • #9
Abhimessi10 said:
By effective velocity I mean resultant velocity
Let me help.

In the ground reference frame an object is moving with velocity ##v## horizontally.

That object fires a projectile with speed ##u##, angle ##\theta## relative to itself - i.e in its frame of reference.

What is the velocity of the projectile in the ground frame? I.e the resultant or effective velocity.
 
  • #10
Abhimessi10 said:
If you don't mind you I could give the link to
the question (video)


He is talking about relative velocity of the ball with respect to ground right ?(ucostheta+v)
 
  • #11
Abhimessi10 said:
He is talking about relative velocity of the ball with respect to ground right ?(ucostheta+v)

I can't see the video, but that makes sense. The velocity of the ball in the ground frame is:

##(v+u\cos \theta, u \sin \theta)##
 
  • #12
Abhimessi10 said:
By effective velocity I mean resultant velocity
After I saw some videos I think that effective velocity is just another case of relative velocity which would depend on the frame of reference as you said
So while solving questions how do you choose the frame of reference?
 
  • #13
Abhimessi10 said:
So while solving questions how do you choose the frame of reference?
You choose the frame of reference that you think will make the problem easiest to solve. This is usually obvious but sometimes a clever change of reference frame make the problem much simpler to solve.
 

What is the difference between relative velocity and effective velocity?

Relative velocity refers to the velocity of an object with respect to a particular reference frame, while effective velocity refers to the velocity of an object taking into account the combined effects of its own velocity and the velocity of the reference frame.

How are relative velocity and effective velocity related?

Relative velocity and effective velocity are related through the principle of Galilean relativity, which states that the laws of physics are the same in all inertial reference frames. This means that the relative velocity of an object in different reference frames will be the same, while the effective velocity may vary depending on the reference frame.

Can relative velocity and effective velocity be the same?

No, relative velocity and effective velocity cannot be the same. Relative velocity is always measured with respect to a specific reference frame, while effective velocity takes into account the combined effects of the object's own motion and the motion of the reference frame. Therefore, even if the relative velocity is zero, the effective velocity may still be non-zero.

How do you calculate relative velocity and effective velocity?

Relative velocity can be calculated by finding the difference between the velocities of two objects or frames of reference. Effective velocity can be calculated by adding the relative velocity and the velocity of the reference frame using vector addition.

In which situations is it important to consider the difference between relative velocity and effective velocity?

It is important to consider the difference between relative velocity and effective velocity in scenarios where the motion of an object is affected by the motion of the reference frame. This can include situations such as moving vehicles, rotating objects, and objects in non-inertial reference frames.

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