# Uniform Circular Motion vs Change in speed of $x$ & $y$ Components

If you are moving at a set rotational speed the x,y components are constantly accelerating and decelerating (aka simple harmonic motion), this is obvious in order to travel in a circular path. My question is how come we don't feel the acceleration and deceleration of the individual components rather we feel a constant centripetal force towards the center of the circle.

• I don't understand what you mean by "feel[ing] the acceleration [...] of the individual components". What exactly do you think should be different? – ACuriousMind Jul 17 '19 at 18:07
• What I am saying is if you just follow the position of the x,y components of a mass in circular motion they are changing speed with the position of the mass.. To my understanding anything that changes speed should reflect a proportional force to the rate of accleration/deceleration. We don't get a proportional force we have a constant force know as centripetal acceleration. – Physicsrocks Jul 17 '19 at 18:23
• The component of force in the x or y direction is not constant. Just the magnitude of the total force is constant. – The Photon Jul 17 '19 at 18:36
• Same reason you don't feel infinite angular velocity walking across the South Pole: They're just coordinates. – JEB Jul 17 '19 at 19:03
• Vector directions are physical, coordinate frames are arbitrary. – Borun Chowdhury Jul 17 '19 at 19:11

Because we feel forces in the directions which they act.

The choice of x and y coordinates is entirely arbitrary. If you rotate your coordinate system 45° for example, you wouldn't expect to suddenly feel forces acting in different directions. The force still acts only in line with the direction it is applied.

Coordinates and orthogonal components become very useful when you have multiple different forces in different directions, and want to analyze the how they interact with each other.

how come we don't feel the acceleration and deceleration of the individual components rather we feel a constant centripetal force towards the center of the circle.

Your body doesn't have any sensors for "absolute" coordinates, only relative ones. There are carnival rides that whip you in a circle without rotation. The car you're in "orbits" the ride, but faces mostly in the same direction (such as North).

When this happens, you definitely feel the acceleration as being backward, left, forward, right, ... and so on.

• It's not just your body, it's physics, c.f. "coordinate-free physics". – JEB Jul 17 '19 at 19:05