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Physics questions

F

FFactory0x

Diamond Member
Why when you smack someone do they feel pain?

Why dont you tailgate

and why when you spin a bottle with water and a ball in it, the water moves to the outside and the ball towards the middle?


Think joules, energy, etc
 
when you smack someone or something, nerve endings called nociceptors in your very-prone-to-pain areas (ex. finger tip. they are everywhere, but very concentrated here) relay an electrical message to your brain that something is hurting you. typical speed from finger tip to brain is over 150mph. as far as physically why, im not sure, but i would guess it has something to do with internal pressure and a rapid change in it, or a breaking point, that when it reaches a certain value it causes the nerves to say "omfg it hurts!" and it sends the message.

edit: derr hit enter too early

why dont i tailgate? like tailgating in a car? because if someone stops before me, it takes time for a human to respond and that delay causes me to stop later than them. the average reaction time of a healthy person at the wheel is 1/4 of a second. that isnt the time it takes you to move your foot - that is the time for you to realize something is wrong. then it takes an additional 1/4 second to move your foot and start stopping, which takes a few seconds as well. you add 1/2 a second of time before you start breaking simply from human reflex limitations. in that time, if you are going 60 miles per hour, which is 88 feet per second, you went an additional 44 feet before you ever STARTED to stop.
 
centrifugal force acts kind of like gravity towards the outside of the bottle so the ball "floats" to the center, if the ball would float on water that is. if it's got higher density it'd "sink" to the side of the bottle
 
as far as the bottle goes, when you spin it (assuming it isnt being translated across the plane (the floor)). the ball would be shooting to the outside if the water wasnt in it. since the water is viscous, it is keeping the ball toward the center, effectively acting like a string tethering the ball. that may be wrong, but i think its right...

anything spinning applies a radial acceleration to anything in or attached to it. the water is being pressed outward because it isnt being held inward by anything, so the tangential acceleration that results from the spinning is contantly trying to throw it at a tangent to its position on the "cicle". if the bottle was open, it would all come out and the bottle would start spinning faster because it lots a ton of its inertia. because momentum (except for friction loss) is conserved, if the intertia goes down, speed goes up. im not too sure about the ball, but i have a feeling its because of the tension of the water...i dont full understand the picture though, so i could be totally off.
 
Originally posted by: FFactory0x
Originally posted by: habib89
you dont' tailgate because f=ma.. you car has a large m so it takes more force to stop the car..
Click to expand...

Thats whats i thought
Click to expand...

i thought you were looking for something less elementary than that...

that doesnt even come close to describing the situation in its entirety...thats just a small part of it. the other car has been stopping for 1/2 a second before you started to stop.

after you reach that point, then you can use simply equations to figure out how much work your car is doing to stop. delta W = K2 - K1. K = 1/2*mass*velocity^2. plug in the mass of your car, the speed you were going, and fill it in. that is how much work your car did stopping.

k2 = when the car is stopped, so your velocity is 0, so that term is 0. that makes k1 negative, which means the acceleration is negative and also makes the work negative.
 
Originally posted by: dighn
centrifugal force acts kind of like gravity towards the outside of the bottle so the ball "floats" to the center, if the ball would float on water that is. if it's got higher density it'd "sink" to the side of the bottle
Click to expand...

centrifugal force is not real though...its a felt effect of radial acceleration and the friction caused by it.

centripital force is the force toward the center (Axis of rotation, whatever you wanna call it). it is parallel with the radial acceleration and is going in the same direction. "centrifugal" is the negative vector of centripital, but it isnt a real force.
 
Originally posted by: Bigsm00th
Originally posted by: dighn
centrifugal force acts kind of like gravity towards the outside of the bottle so the ball "floats" to the center, if the ball would float on water that is. if it's got higher density it'd "sink" to the side of the bottle
Click to expand...

centrifugal force is not real though...its a felt effect of radial acceleration and the friction caused by it.
Click to expand...

yes but the effect is kind of like gravity. once you can draw that parallel it's just a matter of applying buyoncy (sp)
 
Originally posted by: dighn
Originally posted by: Bigsm00th
Originally posted by: dighn
centrifugal force acts kind of like gravity towards the outside of the bottle so the ball "floats" to the center, if the ball would float on water that is. if it's got higher density it'd "sink" to the side of the bottle
Click to expand...

centrifugal force is not real though...its a felt effect of radial acceleration and the friction caused by it.
Click to expand...

yes but the effect is kind of like gravity. once you can draw that parallel it's just a matter of applying buyoncy (sp)
Click to expand...

yeah, thats true. but i dont think they know that, so i was just trying to keep them from being confused.
 
Originally posted by: FFactory0x
Wow. Bigsm00th. You are the man. That was extremely detailed. How the hell do you know all that stuff. Incredible
Click to expand...

dighn probably knows more than me about this stuff to be honest, but to answer your question im a physics/CE major.
 
Originally posted by: dighn
Originally posted by: Bigsm00th
Originally posted by: dighn
centrifugal force acts kind of like gravity towards the outside of the bottle so the ball "floats" to the center, if the ball would float on water that is. if it's got higher density it'd "sink" to the side of the bottle
Click to expand...

centrifugal force is not real though...its a felt effect of radial acceleration and the friction caused by it.
Click to expand...

yes but the effect is kind of like gravity. once you can draw that parallel it's just a matter of applying buyoncy (sp)
Click to expand...

the spinning bottle thing is best related to a centifuge. (ahem...centrifugal force)
when they spin a your vial of blood around, the heavier elements spin to the outside and the lighter elements are closer to the center.

actually..there is no such 'force' as centrifugal force, it is actually the absence of centripetal force.

Centrifugal Force
A non existent force which is actually the absence of a centripetal force.
Centripetal Force
A center seeking net force that is required to keep moving objects in a circular path. If the requirement is not met, then objects move into larger curved paths or go off on a tangent as they follow Newton's First Law.
 
Originally posted by: Bigsm00th
Originally posted by: FFactory0x
Wow. Bigsm00th. You are the man. That was extremely detailed. How the hell do you know all that stuff. Incredible
Click to expand...

dighn probably knows more than me about this stuff to be honest, but to answer your question im a physics/CE major.
Click to expand...

yeah...a physics major must know his physics stuff. kudos to you.
 
Im a finance major and i dont know jack. Well guess im just too used to Gui's doing all the work for me instaed of long hand like they teach
 
Originally posted by: cerebusPu
Originally posted by: Bigsm00th
Originally posted by: FFactory0x
Wow. Bigsm00th. You are the man. That was extremely detailed. How the hell do you know all that stuff. Incredible
Click to expand...

dighn probably knows more than me about this stuff to be honest, but to answer your question im a physics/CE major.
Click to expand...

yeah...a physics major must know his physics stuff. kudos to you.
Click to expand...

cant tell if you are being sarcastic, and i dont see why you would be, but if you arent, thanks. i really enjoy learning about this stuff and it never gets boring. its fun for me to be able to look around and understand why things are they way they are.
 
Originally posted by: cerebusPu
Originally posted by: dighn
Originally posted by: Bigsm00th
Originally posted by: dighn
centrifugal force acts kind of like gravity towards the outside of the bottle so the ball "floats" to the center, if the ball would float on water that is. if it's got higher density it'd "sink" to the side of the bottle
Click to expand...

centrifugal force is not real though...its a felt effect of radial acceleration and the friction caused by it.
Click to expand...

yes but the effect is kind of like gravity. once you can draw that parallel it's just a matter of applying buyoncy (sp)
Click to expand...

the spinning bottle thing is best related to a centifuge. (ahem...centrifugal force)
when they spin a your vial of blood around, the heavier elements spin to the outside and the lighter elements are closer to the center.

actually..there is no such 'force' as centrifugal force, it is actually the absence of centripetal force.

Centrifugal Force
A non existent force which is actually the absence of a centripetal force.
Centripetal Force
A center seeking net force that is required to keep moving objects in a circular path. If the requirement is not met, then objects move into larger curved paths or go off on a tangent as they follow Newton's First Law.
Click to expand...

QFT. thats what i meant when i said it is trying to throw the water tangentially to the axis of rotation, but maybe that didnt make sense to anyone but me.
 
Originally posted by: Bigsm00th
Originally posted by: cerebusPu
Originally posted by: Bigsm00th
Originally posted by: FFactory0x
Wow. Bigsm00th. You are the man. That was extremely detailed. How the hell do you know all that stuff. Incredible
Click to expand...

dighn probably knows more than me about this stuff to be honest, but to answer your question im a physics/CE major.
Click to expand...

yeah...a physics major must know his physics stuff. kudos to you.
Click to expand...

cant tell if you are being sarcastic, and i dont see why you would be, but if you arent, thanks. i really enjoy learning about this stuff and it never gets boring. its fun for me to be able to look around and understand why things are they way they are.
Click to expand...

no no..Im not being sarcastic. i think physics majors are truly capable of abstract theory and complex math.

thats and also my dad's a physics professor and he made me believe that. heh.
 
Originally posted by: cerebusPu

no no..Im not being sarcastic. i think physics majors are truly capable of abstract theory and complex math.

thats and also my dad's a physics professor and he made me believe that. heh.
Click to expand...

i didnt think you were, but this is AT after all, and some people strike at any opportunity. i was just making sure 😀

abstract thinking is basically a requirement to be able to do a lot of physics. some stuff just isnt tangible to understand, so you must be able see it in front of you when there really isnt anything there. its like when you do calculus and they give you an equation like x = 5cos(theta) in 3-space. you have to see it as a circle with radius 2.5 symmetric to the x-axis and the z-axis is an element of its cylindrical translation through space. that is a VERY elementary problem, but its a good one to start with because of its relative simplicity to the rest of calculus (in this area).
 
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