How would we define a value for acceleration if only the direction is changing?

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SUMMARY

Acceleration is defined as the time derivative of velocity, represented mathematically as ##\vec a = d\vec v/dt##. In scenarios where speed remains constant, such as uniform circular motion, the velocity can be expressed as ##\vec v = v\vec e##, where ##\vec e## is a unit vector. The resulting acceleration is given by ##\vec a = v (d\vec e/dt)##, indicating that acceleration occurs due to changes in direction rather than speed. This phenomenon is exemplified by centripetal acceleration, which directs towards the center of the circular path.

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Homework Statement
How would we define a value for acceleration if only the direction is changing and not the speed?
Relevant Equations
acceleration has both speed and direction
How would we define a value for acceleration if only the direction is changing and not the speed?
 
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Acceleration is the time derivative of velocity, not speed. It is defined as ##\vec a = d\vec v/dt##.

Edit: If speed ##v## is constant, then ##\vec v = v\vec e## where ##\vec e## is a unit vector. The acceleration would then be ##\vec a = v (d\vec e/dt)##, ie, the speed multiplied by the derivative of the unit direction.
 
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mancity said:
Homework Statement: How would we define a value for acceleration if only the direction is changing and not the speed?
Relevant Equations: acceleration has both speed and direction

How would we define a value for acceleration if only the direction is changing and not the speed?
The most common example of this is uniform circular motion, where an object or particle moves in a circle at constant speed. In this case, the acceleration vector points to the centre of the circle. This is known as centripetal acceleration. See, for example:

https://byjus.com/physics/uniform-circular-motion/

Or, a more advanced analysis here:

https://openstax.org/books/university-physics-volume-1/pages/4-4-uniform-circular-motion
 
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