# The Feeling of Accelerated Motion

1. Jul 31, 2007

### nealh149

I've read some theories (for example Mach's principle of distant stars being the basis) of why we feel accelerated motion. What are modern sciences thoughts on this?

Couldn't it simply be collisions of particles against nerves just like the seat of a car pushes up against you in an accelerating car?

2. Jul 31, 2007

### DaveC426913

Yeah.

I'm kind of curious about these "theories". Do the proponents of them feel that why we feel what we do is an unanswered question?

3. Jul 31, 2007

### Danger

Yeah, that sounds like a sort of strange question. The various parts of our bodies don't have the same inertia, so they interact differently under acceleration.

4. Jul 31, 2007

### nealh149

I guess the question is why isn't acceleration relative motion, what makes it distinguishable between reference frames.

5. Jul 31, 2007

### Danger

Maybe it's just the beer, but that last post of yours just made no sense whatsoever to me.

6. Jul 31, 2007

### Staff: Mentor

No, it's not the beer, because I'm drinking wine at the moment (in moderation of course). The OP is going to Cornell next year, which may explain the question.... J/K

7. Aug 1, 2007

### Danger

Well, I'm on the last of my beer, but I've still got a couple of W's Corona left, and a dozen ounces or so of tequila. Maybe by the time they're gone, I can interpret that question.

8. Aug 1, 2007

### nealh149

Sorry guys, let me try to rephrase this. I don't know if you ever heard Newton's Bucket problem, but here it goes:

If you had a water filled bucket and spin it, the water will become concave and push up against the sides of it. If you somehow suspended this bucket in empty space (a theoretical space where no other matter exists) would it still be concave. In other words, the bucket wouldn't have any external cues to measure it's rotation against, but could it still "feel" it internally?

9. Aug 1, 2007

### ZapperZ

Staff Emeritus
Yes, because the bucket and the water have inertia. Inertia is independent of gravitational field.

Zz.

10. Aug 1, 2007

### DaveC426913

Accelerated motion can only occur as a result of a force. We feel that force.

If you are way out in outer space such that you have no reference frame to give you clues, you can still tell if there is a force acting upon you. The corollary is that if you are not experiencing a force, you are not accelerating, you are in a state of inertial motion.

The bucket knows if it is experiencing a force; it is experiencing the centripetal force of the rope pulling it out of its straight-line inertial motion.

11. Aug 1, 2007

### rcgldr

Humans feel the force due to compression at the point of contact, and fluid pressure from accelerated blood.

12. Aug 1, 2007

### D H

Staff Emeritus
The OP appears to be asking about Mach's Principle, which attempts to explain why inertia exists and which is embodied in the mathematics of General Relativity. So answering that the reason we feel acceleration because of inertia is taking a step backward.