Lol, I'm still not understanding it from your guys's explanations, the book, or Wikipedia.
To put it bluntly, I remember our teacher telling us that one was a "fictitious force". You're following a trajectory, but this makes it feel outward. I'm pretty sure this was centrifugal. Like the spaceship ride at the carnival.
Centripetal is the inward push?
I'm at the point where I might skip this question if asked. (We can skip four.). If he even asks this.
But I'd rather skip the quantum mechanics stuff than something this "easy."
Pretend you have a baby that only knows how to crawl forward... always wants to go straight ahead in a straight line (in this model, we replace the "inertia" of a frictionless moving object, with the inexorable, purposeful crawl of the baby because its easier to 'feel' whats going on)
Attach a rope to the SIDE of the baby, and attach the other end of the rope to a post in the ground. the rope tugs the baby perpendicular to its forward direction that "inertia" would normally take the baby. Baby keeps trying to crawl in a straight line, but the rope forces the baby to go in a circle. The baby just goes in a circle... but it really is trying to go off in a tangent from that circle... and would go straight off in a tangent were it not for the constraint of the rope tugging it towards to pole. That is the centripetal force applied by the rope on the baby. If the rope ever breaks, the baby will simply keep going in a straight line tangential to the circle.
Its obvious at slow speeds of baby crawling that this is what is going on.
If the baby crawls faster and faster, the amount of centripetal force that the rope applies to the baby goes higher. The tug of that rope on that baby's side feels stronger. That is centripetal force.
I think some confusion comes from out BAD "intuition" that tells us that IF THE ROPE BREAKS, we will fly AWAY From the circle RADIALLY, because there is some kind of "centrifugal force" away from the circle.
There is no "centrifugal force" pushing the baby away from the circle.
There is only "centripetal force" pushing the baby's side, and keeping it from doing what it wants to do (go in a straight line).
As soon as you break the rope, the baby (now free from the centripetal force) just keeps moving (at the same speed and direction the baby was crawling at the moment the rope broke) in a STRAIGHT LINE at a tangent to the circle.
The ILLUSION (and our intuition) is that the baby is flying away from the center of the circle, but REALITY is that its only moving along its original line at the point of rope breakage (As the baby gets further and further way from the circle though, the the illusion that the baby flew away from the center becomes even stronger, since the circle is so far away, that it just looks like the baby "escaped" the circle...).
Objects move straight due to inertia. A rope constraining that movement, prevents that by applying centripetal force perpendicular to the movement.
So a centripetal force is only apparent if your frame of reference is moving? And it pushes inward?
I'd say centripetal force only EXISTS if your frame of reference is moving (i.e. accelerating in a direction perpendicular to your motion).
I always had trouble getting a "feel" for why "centripetal force" was "interesting" or important in any way... the classic string on a ball.
I finally came to think of the ball on a string as just a "special case" or subset of a larger class of body problems in which ANY acceleration force is applied perpendicular to the direction the object is moving (e.g. by a string or by gravity) so that the object doesn't change speed, but does change direction.
So throwing a ball or firing a bullet horizontally... and watching it initially start to drop, starts out very similar in behavior to an object in a circular orbit. A fired bullet slows down due to friction. Now if you get rid of atmosphere and have a frictionless environment, as gravity makes the bullet accelerate towards the center of the earth, the trajectory of the bullet gains a downward component, and this downward component is in the same direction as the acceleration force of gravity.... thus making the bullet speed up!
Now, if a series of bullets is fired each with incrementally higher velocities, the rate of curvature of each bullet path will become less, and each bullet will hit the ground farther away... until you finally fire a bullet fast enough to follow a path that follows the curvature of the earth... by following the curvature of the earth, the force of gravity will ALWAYS be perpendicular to the flight of the bullet, the bullet will never speed up, and it will go in a circle around the earth at constant speed. And you have your centripetal acceleration supplied by the gravity of the earth.
Now if there is a tiny ant passenger on this bullet, will it ever feel "accelerated" against the bullet? Nope. Because you are in "free fall" where your tendency to move away from the earth is exactly canceled by the force of gravity.
Now I'm ignoring the fact that orbits aren't usually circular, and that we're not talking about point masses, etc. but I think the thought exercise of ALL circular motions and what makes circular motions happen makes it easier to go back and look at the original concept of centripetal acceleration a little differently.
We normally think of circular motion as in centrifuges producing great force, and "centripetal force" being required to keep things from flying away, etc.
But ironically, the more common situation is orbits where no energy is being applied to anything, and the object that's doing the orbiting is in "free fall" orbit, and nobody on board would feel much sense of being pulled in any direction.
Sorry, that was probably more confusing than helpful.
Centrifugal force pushes outward and keeps the water in the bucket?
Water should stay in the bucket by default, even when you don't apply a force to it. The bucket is pushed in against the water.
I visualize a jet ski approaching waves from a boat wake... Or running away... Or having to shake hands with a line of people walking towards you... If you walk towards them too, more handshakes/second.
On the first question, though, I hate to use speed to characterize things in relativity because sometimes I feel the terms are ambiguous. I like to think in terms of events (waves encountered) and time. "come at you faster" just feels ambiguous.
Frequency you hear is determined by the number waves that reach your ear per second.
I would say that as I approach a wave source, the number of waves that hit my ear per second increases, and as I move away, the number of waves that hit my ear per second decreases.
though maybe others would find that more confusing.
I thought one of the laws of thermodynamics was heat always transfers hot to cold.
Edit:
Dcartist, the project / miniature lab says to turn on a light bulb that's been off for a while. Then turn it on for a couple minutes then touch it.
The way the question is originally worded is confusing at best. This clarification helps a little, but I'm not 100% certain we're getting the whole question. Sounds like an incandescent bulb. Generates light via raising its temperature and thus its black body radiation ( which is more infrared than visible energy )
The problem with the first answer that was offered, is the fact is that if your hand feels warmed by infrared from the bulb at an inch or two away from the filament, then it should feel even more warmed when you touch the glass and thus are only a few mm from the filament. Radiation falls off as 1/squareofdistance from source. So you get 1/4 of the IR radiation at twice the distance from the filament.
The correct answer is that your finger's temperature is way above room temperature and there is poor heat conduction from finger to air. However, there is much better heat conduction from your hand to the near room temperature glass when they touch.
That difference In heat conduction loss is much greater than the tiny amount of IR energy you receive at either point.
It's like when your hand is near the bulb, it's losing .001 to the air and gaining .01 from the IR. when your hand touches the glass it's losing .5 to the glass and gaining .04 from the IR. (made up numbers, but you get the picture)
The project does not say to touch a bulb that's been on for a while.
Okay, I can't find the answer to this on the internet. Looking pretty hard.
Why does a lightbulb feel warm when you hold your hand up to it but is room temperature when you touch it?
Is it because the light bulb is clear so it gives off all it's radiant energy through radiation and thus sends waves of heat toward your hand? If a lightbulb was murky or colored in some way would it be hot to the touch?
You can't find it on the Internet because it's not true.
I know of no kind of common lightbulb that makes light that doesn't produce heat too, AND get hot to the touch. Incandescents are too hot to touch without getting burned. CFLs are uncomfortably hot to painful depending on wattage (24s are quite hot). LEDs are definitely hot as well, they have fins on them to radiate heat away.
Is there something else in the question that clarifies it a little?
The change in the speed of separation due to safe does not have to do with density. Soap is an emulsifier. Just check out the wiki on emulsions and you'll see what it's about.
Depends on your time scale. For the purposes of all life on Earth, atoms can't be destroyed. Unstable ones will decay into lighter and more stable atoms and that's it.
But things change if you're willing to sit down and wait a few aeons. Some grand unified theories predict that protons are unstable and also decay so that after a very, very, very long time all atoms will be destroyed.
Another possibility is that if gravity ends beating the dark energy repulsion, then all matter will eventually be collected into black holes. End of atoms as we know them.
But if the dark energy repulsion beats the gravitational attraction, a possible scenario is the "Big Rip". The repulsion is so strong that galaxies, planets and eventually atoms are torn apart and destroyed.
Interestingly... outside the realm of the "life of the universe" time frames, in "day to day" use, atoms generally stay the same size, or get smaller through decay...
Fusion is the main process by which we get bigger atoms from smaller ones, and this occurs mostly in stars. Stars like the sun have energetic enough fusion to make helium from hydrogen (and trace amounts of slightly bigger atoms).
Bigger stars than the sun are required to make large amounts of atoms heavier than helium.
All of the REALLY heavy atoms (bigger than iron, e.g. uranium) were formed in supernovae.
But luckily only a very, very, very tiny percentage of atoms "break" into smaller ones in "day to day" use. Hitting them with high energy stuff will split them into smaller atoms, but it usually has to be pretty damn high energy.
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Some of that might be wrong... but that's how I think of atoms: "Forged" in superhigh energy environments (supernovae for big atoms, big stars for medium atoms, and regular size and smaller stars to make helium), they require a lot of energy to shatter on command. However, they do 'decay' and break up, but "stable" atoms have half lives so long that I don't think we even know what the number is.
When you pull a thread from a spool, it doesn't matter what direction you pull the thread.
Whenever you pull string away from a spool, it always rotates the spool in a direction that brings the point A on the spool (that has string that is about to lift off the spool) to move towards the point B on the spool (that has string that has just lifted off the spool).
Thus the spool always rotates from the more proximal string towards the more distal string on the spool.
"You push a heavy car by hand. The car, int urn, pushes back on you with an opposite but equal force on you. Doesn't this mean that the forces cancel one another, making acceleration impossible? Why or why not?"
When the car actually starts to move, you actually have to push off the ground with more force than the static resistance the car. When the car is accelerating and moving you have to push with a force exceeding the rolling resistance. when you push it, the car is moving relative to the ground. It's not moving relative to your hand.
If this is some more general question about how can anything ever move or be accelerated at all, since everything "pushes back"... Well i think there's just a tiny bit of confusion here.
The forces you're describing are the force that holds your hand to the car and crushes the skin cells and the clear coat, just as your foot pushes on your ankle and your ankle pushes back, and the force that your ankle pushes on your tibia and your tibia pushes back, femur, hips, spine, shoulders, arms, hands, etc. those forces are all there... And keep the car attached to your hands and not moving relative to your hands.
It's like lifting a stack of dishes off the ground. There is static forces between your hand and the plate and each plate from the next. Each plate exerts force on the plate touching it, but they all stay stationary RELATiVE to each other. You can't start mentally adding those forces together because you just end up with infinity. Drawing diagrams helps to understand it better.
Attach a rope to the SIDE of the baby, and attach the other end of the rope to a post in the ground. the rope tugs the baby perpendicular to its forward direction that "inertia" would normally take the baby. Baby keeps trying to crawl in a straight line, but the rope forces the baby to go in a circle. The baby just goes in a circle... but it really is trying to go off in a tangent from that circle... and would go straight off in a tangent were it not for the constraint of the rope tugging it towards to pole. That is the centripetal force applied by the rope on the baby. If the rope ever breaks, the baby will simply keep going in a straight line tangential to the circle.
Its obvious at slow speeds of baby crawling that this is what is going on.
If the baby crawls faster and faster, the amount of centripetal force that the rope applies to the baby goes higher. The tug of that rope on that baby's side feels stronger. That is centripetal force.
I think some confusion comes from out BAD "intuition" that tells us that IF THE ROPE BREAKS, we will fly AWAY From the circle RADIALLY, because there is some kind of "centrifugal force" away from the circle.
There is no "centrifugal force" pushing the baby away from the circle.
There is only "centripetal force" pushing the baby's side, and keeping it from doing what it wants to do (go in a straight line).
As soon as you break the rope, the baby (now free from the centripetal force) just keeps moving (at the same speed and direction the baby was crawling at the moment the rope broke) in a STRAIGHT LINE at a tangent to the circle.
The ILLUSION (and our intuition) is that the baby is flying away from the center of the circle, but REALITY is that its only moving along its original line at the point of rope breakage (As the baby gets further and further way from the circle though, the the illusion that the baby flew away from the center becomes even stronger, since the circle is so far away, that it just looks like the baby "escaped" the circle...).
Objects move straight due to inertia. A rope constraining that movement, prevents that by applying centripetal force perpendicular to the movement.
I always had trouble getting a "feel" for why "centripetal force" was "interesting" or important in any way... the classic string on a ball.
I finally came to think of the ball on a string as just a "special case" or subset of a larger class of body problems in which ANY acceleration force is applied perpendicular to the direction the object is moving (e.g. by a string or by gravity) so that the object doesn't change speed, but does change direction.
So throwing a ball or firing a bullet horizontally... and watching it initially start to drop, starts out very similar in behavior to an object in a circular orbit. A fired bullet slows down due to friction. Now if you get rid of atmosphere and have a frictionless environment, as gravity makes the bullet accelerate towards the center of the earth, the trajectory of the bullet gains a downward component, and this downward component is in the same direction as the acceleration force of gravity.... thus making the bullet speed up!
Now, if a series of bullets is fired each with incrementally higher velocities, the rate of curvature of each bullet path will become less, and each bullet will hit the ground farther away... until you finally fire a bullet fast enough to follow a path that follows the curvature of the earth... by following the curvature of the earth, the force of gravity will ALWAYS be perpendicular to the flight of the bullet, the bullet will never speed up, and it will go in a circle around the earth at constant speed. And you have your centripetal acceleration supplied by the gravity of the earth.
Now if there is a tiny ant passenger on this bullet, will it ever feel "accelerated" against the bullet? Nope. Because you are in "free fall" where your tendency to move away from the earth is exactly canceled by the force of gravity.
Now I'm ignoring the fact that orbits aren't usually circular, and that we're not talking about point masses, etc. but I think the thought exercise of ALL circular motions and what makes circular motions happen makes it easier to go back and look at the original concept of centripetal acceleration a little differently.
We normally think of circular motion as in centrifuges producing great force, and "centripetal force" being required to keep things from flying away, etc.
But ironically, the more common situation is orbits where no energy is being applied to anything, and the object that's doing the orbiting is in "free fall" orbit, and nobody on board would feel much sense of being pulled in any direction.
Sorry, that was probably more confusing than helpful.
Water should stay in the bucket by default, even when you don't apply a force to it. The bucket is pushed in against the water.
On the first question, though, I hate to use speed to characterize things in relativity because sometimes I feel the terms are ambiguous. I like to think in terms of events (waves encountered) and time. "come at you faster" just feels ambiguous.
Frequency you hear is determined by the number waves that reach your ear per second.
I would say that as I approach a wave source, the number of waves that hit my ear per second increases, and as I move away, the number of waves that hit my ear per second decreases.
though maybe others would find that more confusing.
The problem with the first answer that was offered, is the fact is that if your hand feels warmed by infrared from the bulb at an inch or two away from the filament, then it should feel even more warmed when you touch the glass and thus are only a few mm from the filament. Radiation falls off as 1/squareofdistance from source. So you get 1/4 of the IR radiation at twice the distance from the filament.
The correct answer is that your finger's temperature is way above room temperature and there is poor heat conduction from finger to air. However, there is much better heat conduction from your hand to the near room temperature glass when they touch.
That difference In heat conduction loss is much greater than the tiny amount of IR energy you receive at either point.
It's like when your hand is near the bulb, it's losing .001 to the air and gaining .01 from the IR. when your hand touches the glass it's losing .5 to the glass and gaining .04 from the IR. (made up numbers, but you get the picture)
maybe helpful just to be 100% sure.
I know of no kind of common lightbulb that makes light that doesn't produce heat too, AND get hot to the touch. Incandescents are too hot to touch without getting burned. CFLs are uncomfortably hot to painful depending on wattage (24s are quite hot). LEDs are definitely hot as well, they have fins on them to radiate heat away.
Is there something else in the question that clarifies it a little?
It's an important concept in sauces.
Fusion is the main process by which we get bigger atoms from smaller ones, and this occurs mostly in stars. Stars like the sun have energetic enough fusion to make helium from hydrogen (and trace amounts of slightly bigger atoms).
Bigger stars than the sun are required to make large amounts of atoms heavier than helium.
All of the REALLY heavy atoms (bigger than iron, e.g. uranium) were formed in supernovae.
But luckily only a very, very, very tiny percentage of atoms "break" into smaller ones in "day to day" use. Hitting them with high energy stuff will split them into smaller atoms, but it usually has to be pretty damn high energy.
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Some of that might be wrong... but that's how I think of atoms: "Forged" in superhigh energy environments (supernovae for big atoms, big stars for medium atoms, and regular size and smaller stars to make helium), they require a lot of energy to shatter on command. However, they do 'decay' and break up, but "stable" atoms have half lives so long that I don't think we even know what the number is.
Sin a1 = sin a2. Defines above or below horizontal axis.
Cos a1 = cos a2. Defines left or right of vertical axis.
They're the same angle. Or multiples of 2pi + the angle.
So θ1-θ2=2*pi*J, where J is an integer.
I think. That's basic trig. But if there's some other thing going on that is not "trig-gy"... It's been 30 years since trig.
But solutions can be roughly simulated on a computer with a massive number of calculations. If those terms are what I think those terms are.
Whenever you pull string away from a spool, it always rotates the spool in a direction that brings the point A on the spool (that has string that is about to lift off the spool) to move towards the point B on the spool (that has string that has just lifted off the spool).
Thus the spool always rotates from the more proximal string towards the more distal string on the spool.
Or am I misunderstanding the question?
When the car actually starts to move, you actually have to push off the ground with more force than the static resistance the car. When the car is accelerating and moving you have to push with a force exceeding the rolling resistance. when you push it, the car is moving relative to the ground. It's not moving relative to your hand.
If this is some more general question about how can anything ever move or be accelerated at all, since everything "pushes back"... Well i think there's just a tiny bit of confusion here.
The forces you're describing are the force that holds your hand to the car and crushes the skin cells and the clear coat, just as your foot pushes on your ankle and your ankle pushes back, and the force that your ankle pushes on your tibia and your tibia pushes back, femur, hips, spine, shoulders, arms, hands, etc. those forces are all there... And keep the car attached to your hands and not moving relative to your hands.
It's like lifting a stack of dishes off the ground. There is static forces between your hand and the plate and each plate from the next. Each plate exerts force on the plate touching it, but they all stay stationary RELATiVE to each other. You can't start mentally adding those forces together because you just end up with infinity. Drawing diagrams helps to understand it better.
And I thought the responses about weak or reduced expression of A or B antigen due to mutation of a protein was just one response.
I didn't realize that your entire question was about about the weak phenotypic Expression of A or B.
I see that there's higher pancreatic cancer risk for people with A or B vs O... Oh I'm just fishing around here. Never mind. Sorry I couldn't help.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2839871/?tool=pmcentrez
My bad.