The nature of water pressure?

[DrMike]

You guys need to go back to school.

 

[Don Burke]

You guys need to go back to school.

Thanks for the insight.

 

[coberry7]

Astronauts do NOt exist in an environment outside most of the effcts of gravity. Instead, in orbit the force of gravity (weight) upon their bodies and their spacecraft is compensated by an equal and oppositely directed force, cenrifugal force. Likewise, a neutral diver's weight is compensated by and equal and opposite force, buoyancy.

Quite correct Don for astronauts in orbit. I should have clarified my statement to reflect astronauts not in orbit under the effects of CENTRIPETAL force as they are slung around the perimeter of a planet. Centrifugal force would sling the spacecraft off on a tangent opposite of the force of gravity, or whatever the heck hose astronauts decided to orbit. Think water in a bucket being slung round and round. If you let go of the bucket it does not travel in a circle, like the astronauts in orbit would.

 

[jonnythan]

Quite correct Don for astronauts in orbit. I should have clarified my statement to reflect astronauts not in orbit under the effects of CENTRIPETAL force as they are slung around the perimeter of a planet. Centrifugal force would sling the spacecraft off on a tangent opposite of the force of gravity, or whatever the heck hose astronauts decided to orbit. Think water in a bucket being slung round and round. If you let go of the bucket it does not travel in a circle, like the astronauts in orbit would.

It doesn't quite work that way.

The centripetal force is gravity. The astronauts and their spaceship are in a freefall in earth's gravitational field. They're just moving perpendicularly to the force with just the right velocity that they never actually get closer to the ground. This is the nature of orbit.

Centrifugal force, on the other hand, is not an actual force. It's a "percieved" force. For example, when you're in a car taking a corner, the "centrifugal" force is the "force" tossing you towards the outside of the turn. It doesn't actually exist. Were you to do any calculations on the astronauts, the only force you'd find on their bodies is gravity.

Since the *only* force they're experiencing is gravity in a downward direction, they're quite literally accelerating straight down in direct proportion to gravity [acceleration is force divided by mass]. The "centrifugal" force pushing them outward is sort of an imaginary concept to compensate for what the body "feels" as it moves in a circular path.

 

[coberry7]

Thanks Jonnythan. Been a while since I studied that stuff.

 

[DrMike]

Centrifugal force, on the other hand, is not an actual force. It's a "percieved" force. For example, when you're in a car taking a corner, the "centrifugal" force is the "force" tossing you towards the outside of the turn. It doesn't actually exist. The "centrifugal" force pushing them outward is sort of an imaginary concept to compensate for what the body "feels" as it moves in a circular path.

Thats a load of rubbish.

 

[cornfed]

Thats a load of rubbish.

Please explain...

 

[jonnythan]

Thats a load of rubbish.

Except for the fact that it's true. Centrifugal force is an "experienced" force, but it doesn't actually exist. If you were to take a physics or dynamics class, you would draw "free body diagrams" of objects. For a body in orbit, you'd draw the force of gravity, and that's it. For a person in a car turning a corner, there's the centripetal force (the car pushing them towards the inside of the turn), the force of your butt down on the seat, the seat pushing back up against you, and a static friction force. There's no centrifugal force, unless you want to count the outward force on the holder of a string or something.

Note: When a body moves in a circle with uniform velocity, a force must act on the body to keep it in the circle without change of velocity. The direction of this force is towards the center of the circle. If this force is applied by means of a string to the body, the string will be in a state of tension. To a person holding the other end of the string, this tension will appear to be directed toward the body as if the body had a tendency to move away from the center of the circle which it is describing. Hence this latter force is often called centrifugal force. The force which really acts on the body being directed towards the center of the circle is called centripetal force, and in some popular treatises the centripetal and centrifugal forces are described as opposing and balancing each other. But they are merely the different aspects of the same stress.

 

[DrMike]

Please explain...

Not disagreeing at all with what hes saying - just the way its said it.

Saying what a body experiences 'doesnt exist' or is 'imaginary' is not very scientific. There is an real inertial force in play with real conseqences. A better way of putting it -

Centrifugal force is actually not a force but the experience of an inertial force experienced in a rotating reference frame acting away from the center of the rotation. It is equal in magnitude but opposite to the centripetal force required to constrain the body to move in a circular motion.

I know, I know Im being an ass - but yould also be in a bad mood if some tosser just vandalised your car

 

[Uncle Pug]

I know, I know Im being an ass - but yould also be in a bad mood if some tosser just vandalised your car

Perhaps you are confusing cause for effect.