Vector Proof Of Constant Speed Means Perpendicular Acceleration.

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SUMMARY

The discussion centers on proving that when speed is constant, the velocity vector V(T) and the acceleration vector A(T) are perpendicular. Participants emphasize the importance of the dot product, which must equal zero to demonstrate this relationship. A key example provided is uniform circular motion, where speed remains constant while acceleration is directed towards the center, highlighting that constant speed does not imply zero acceleration. The necessity of applying the product rule for differentiating dot products of vectors is also noted as a crucial step in the proof.

PREREQUISITES
  • Understanding of vector mathematics, specifically dot products.
  • Familiarity with the concepts of velocity and acceleration as vectors.
  • Knowledge of uniform circular motion and its implications on speed and acceleration.
  • Basic calculus, particularly the product rule for differentiation.
NEXT STEPS
  • Study the properties of dot products in vector calculus.
  • Learn about uniform circular motion and its characteristics in physics.
  • Review the product rule for differentiation in the context of vector functions.
  • Explore the relationship between speed, velocity, and acceleration in various motion scenarios.
USEFUL FOR

Students of physics, particularly those studying mechanics, as well as educators and anyone seeking to deepen their understanding of vector relationships in motion.

Baumer8993
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Homework Statement



Prove that when speed is constant that V(T), and A(T) are perpendicular.

Homework Equations



I know this involves the dot product to show that the dot product of the vectors is zero.


The Attempt at a Solution



In my head I thought that since the speed is constant that there must be no acceleration. When I dot the zero acceleration vector to the velocity vector it is zero, but I am thinking that there is no way this can be right.
 
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What is "speed"? I'm guessing V and A are vectors
 
Baumer8993 said:

Homework Statement



Prove that when speed is constant that V(T), and A(T) are perpendicular.

Homework Equations



I know this involves the dot product to show that the dot product of the vectors is zero.


The Attempt at a Solution



In my head I thought that since the speed is constant that there must be no acceleration. When I dot the zero acceleration vector to the velocity vector it is zero, but I am thinking that there is no way this can be right.
How does speed relate to velocity? Your book should give a definition for speed.
 
Baumer8993 said:

Homework Statement



Prove that when speed is constant that V(T), and A(T) are perpendicular.

Homework Equations



I know this involves the dot product to show that the dot product of the vectors is zero.


The Attempt at a Solution



In my head I thought that since the speed is constant that there must be no acceleration. When I dot the zero acceleration vector to the velocity vector it is zero, but I am thinking that there is no way this can be right.

That isn't true. For example, in uniform circular motion the speed is constant but the acceleration is nonzero towards the center. Think about differentiating ##\vec V\cdot \vec V##.
 
How do you differentiate v dot v?
 
It is a product. How do you differentiate a product?

ehild
 
Oh well duh that makes sense.
 
Of course, you first have to prove that the product rule works for dot products of vectors.
 

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