3D Velocity Of A Moving Object To A Stationary Object

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    3d Velocity
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Discussion Overview

The discussion centers on calculating the speed of a moving object (Object 2) towards or away from a stationary object (Object 1) in a 3D space. The focus is on the mathematical approach to determine the rate of change of distance between the two objects based on Object 2's velocity and position.

Discussion Character

  • Mathematical reasoning

Main Points Raised

  • One participant describes the need to calculate the speed at which Object 2 is moving towards or away from Object 1, emphasizing that this is not simply Object 2's speed.
  • Another participant suggests that to find the rate of change of distance between the objects, one must determine the component of Object 2's velocity that is parallel to its position vector relative to Object 1.
  • A subsequent participant confirms they have Object 2's position and requests further details on the calculation process.
  • Another reply indicates that the calculation involves finding a unit vector pointing from Object 1 to Object 2 and using the scalar product of Object 2's velocity with that unit vector to determine the velocity component in that direction.

Areas of Agreement / Disagreement

Participants generally agree on the mathematical approach needed to calculate the speed towards or away from Object 1, but the discussion remains unresolved regarding the specific steps and details of the calculation.

Contextual Notes

Participants have not fully detailed the assumptions regarding the positions and velocities involved, nor have they resolved the mathematical steps necessary for the calculation.

phys123
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There are 2 objects. Object 1 is stationary and Object 2 is in motion. Object 1's position in the 3D world is (x=0,y=0,z=0). I have Object 2's velocity (also in x,y,z directions). I need to calculate the speed at which Object 2 is moving towards (or away from) Object 1. Keep in mind that this will not be Object 2's speed, because it is not moving directly towards Object 1. It is moving on it's own path, but I need to know the change in speed towards Object 1. Hope I explained that good enough, if not then ask. How can this be done?
 
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You'll need Object 2's position. At any moment, find the component of Object 2's velocity parallel to its position vector with respect to the origin. That will be the rate of change of the distance between the Objects.
 
I do have Object 2's position, forgot to mention that. And what you are saying is exactly what I need to do. Can you go into detail on how I would calculate this? My physics isn't very strong
 
Not much physics here, just a bit of math. Find the unit vector pointing from 1 to 2--that gives you the direction. To find the component of 2's velocity in that direction, take the scalar product of the velocity with that unit vector.
 

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