Another "simple" physics question.

"In other words, people understood what I meant."

Ummm, try saying that on a college exam. In physics, you have to be SPECIFIC. You don't see NASA engineers assuming the distance between the earth and mars do you? Your question is worded so poorly, you'd spend all your time trying to figure out what exactly the author meant.

 

OK, the question was worded incorrectly. Interpreted correctly by the wording, there is no correct answer choice available (moving at constant speed). The nearest correct answer would be not moving, which would be true if it was asking about linear motion. Since we know Ferris wheels move in circles while not moving forward...

OK, bad question. Most people did get it right according to what I meant to ask. Those who answered C got it right according to what was actually being asked.

Sorry.

 

It depends on which direction the wheel is turning.

 

;

 

the only time it APPEARS TO BE accelerating is when a set point on the wheel passes the stationary person on the ground, IN EITHER DIRECTION. Look up the word RELATIVITY in the dictionary.

 

Yeah, what he said!

 

never! i dont want to fuel this discussion

 

NO. If the person on the wheel was continually accelerating it would be the same as saying thay were continually GAINING SPEED which THEY ARE NOT. If this were the case they would soon reach the speed of light and no longer exist as matter but would turn into energy.

They are rotating at a CONSTANT RATE.

 

Correct. It does not require acceleration to change direction.

 

Period.

 

This entire thread reminds me of the company I work for that has engineers that take something simple and complicate the hell out of it.
It's only when their results are put into use by the "relatively uneducated" that they find out they left out one key factor in their computations. COMMON SENSE

 

No that is wrong.

That's the funny thing about circular motion. It is always changing direction. Acceleration is a vector and has a direction component. Since the person is always going in a new direction, they are always accelerating, even when their speed is constant. In circular motion, acceleration is given as velocity squared divided by the radius of the circle.

That is actually what the question was trying to get at.

You are right about the rotation at constant rate. That rotation at a constant rate (circular motion at constant velocity) is achieved with constant acceleration. Strange but true.

 

Taken from Websters,

"accelerate"
One entry found for accelerate.
Main Entry: ac·cel·er·ate
Pronunciation: -l&-"rAt
Function: verb
Inflected Form(s): -at·ed; -at·ing
Etymology: Latin acceleratus, past participle of accelerare, from ad- + celer swift -- more at HOLD
transitive senses
1 : to bring about at an earlier time
2 : to cause to move faster; also : to cause to undergo acceleration
3 a : to hasten the progress or development of b : INCREASE <accelerate food production>
4 a : to enable (a student) to complete a course in less than usual time b : to speed up]/b] (as a course of study)
intransitive senses
1 a : to move faster : gain speed b : GROW, INCREASE <inflation was accelerating>
2 : to follow an accelerated educational program



By taking note of the highlighted parts of the definition I still fail to see how the process of acceleration would apply to the static condition of a constant state of rotation. Nothing is going anywhere but in a circle and it definitley isn't going anywhere faster if the wheel is kept at constant speed.

I think the wall I am hitting here is the technical definitions and concepts that aren't usually used on a level most would consider "lay terms".

To me, a wheel that makes one revolution every 60 seconds is a constant. Nothing will change the fact that the same point on the wheel will pass by at exactly 60 seconds as long as the wheel maintains constant speed. In the world of physics that is considered a constant.

I suppose in more technical terms it can be explained that there is acceleration because of change of direction BUT the acceleration itself becomes a constant because the speed of rotation does not change and the acceleration does not change with it.

[size=+1]Would that not cancel the concept of acceleration when changing direction?[/size]

to cause to move faster

to hasten the progress

to speed up

to move faster

Inquiring minds want to know.

 

Art, Thanks for your explanation but it is going to take a while for me to wrap my head around the concept of accelerating while maintaining constant speed.

That term in itself is an enigma, at least to me. We are using the term accelerate to mean two different things.

I guess it's because of my spotty knowledge after reading books about this for 30 years or so but never indulging in the more formal and technical aspects of what you pose.

 

This is the same as stretching a spring and having it go back and forth. The same motion is made with a rotating wheel with a single point on it and shining light on it to make a shadow. I did this in physics lab in high school. There is constant acceleration, even when the object changes direction where the velocity appears to be 0. That's actually when acceleration is the greatest.

 

I hope this will help



Centripetal Acceleration: In order for an object to execute circular motion - even at a constant speed - the object must be accelerating towards the center of rotation. This acceleration is called the centripetal or radial acceleration and has a magnitude of

centripetal acceleration (m/s^2) = (v^2)/r

As said earlier, acceleration is a change in direction or velocity




With reference to the person/chair on the wheel - it is always accelerating

with reference to the ferris wheel on the ground - it is not moving

 

In circular motion, there is acceleration. It's called centripital accleration (sp?). This is one way to make gravity in a spacecraft in space. Acceleration = velocity^2/radius.

If you fill a bucket with water and spin it by the handle while rotating around your feet, the water won't spill out (you can also rotate it upwards where the bucket will be upside down at its peak). The accleration (man made gravity) is holding the water from falling out. Even though you're rotating it at a constant velocity, the accleration is directed away from you pushing the water to the bottom of the bucket.

 

I understand all of the concepts you guys are talking about but don't have the technical background to put it into equation.
Dang, Now I have to look up more big words in the dictionary......................................

I guess thats why you guys drive the cool cars and I drive a 308

 

might have more luck with the glossary of a physics text book (or online equivalent) than a standard dictionary

as i am sure you are well aware, the english language has a lot of ambiguous terms that may or may not always be used in the proper context

 

I think ambiguous is the key word here. Now if I can drag my face out of my Weber carburetor book for a while I might learn something.

 

My $.02 opinion. A circle has no start point nor a stop point--therefore if it is moving at a constant R.P.M. the 12:00/6:00 position is moving at the same speed at the 9:00/3:00 position or any other 180 degree opposed pair. Thus the only difference is the SPACIAL perception of the person who is standing on the ground. Depending how he is looking at the wheel (assuming directly under the wheel) the people descending may appear to be moving more slowly than the people ascending or vice-versa depending on the observation position of the ground related viewer.
_________________________________________________________________
"There are two kinds of people; those who work and those who take credit for the work. It is best to be in the first group, for there is less competition!

 

One of the most ambiguous terms I have ever used is "Your honor" with a certain Marin county judge.

 

Acceleration is defined as "rate of change of VELOCITY," and not as "rate of change of SPEED."

The guy is moving at a constant SPEED, but not at constant VELOCITY.

Therefore, he is ACCELERATING.

I say it is time for you to take that basic physics course again.

Agreed.

 

What basics physics course?

 

Your statement doesn't make sense. How can a person be moving at constant velocity but not a constant speed when they mean EXACTLY the same thing?

[size=+1]VELOCITY[/size]
Main Entry: ve·loc·i·ty
Pronunciation: v&-'lä-s&-tE, -'läs-tE
Function: noun
Inflected Form(s): plural -ties
Etymology: Middle French velocité, from Latin velocitat-, velocitas, from veloc-, velox quick; probably akin to Latin vegEre to enliven -- more at WAKE
1 a : quickness of motion : SPEED <the velocity of sound> b : rapidity of movement <[my horse's] strong suit is grace & personal comeliness, rather than velocity -- Mark Twain> c : speed imparted to something <the power pitcher relies on velocity -- Tony Scherman>
2 : the rate of change of position along a straight line with respect to time : the derivative of position with respect to time
3 a : rate of occurrence or action : RAPIDITY <the velocity of historical change -- R. J. Lifton> <the narrative leaps from one frantic episode to another with impressive velocity -- James Atlas> b : rate of turnover <the velocity of money>

[size=+1]SPEED[/size]
Main Entry: 1speed
Pronunciation: 'spEd
Function: noun
Etymology: Middle English spede, from Old English spEd; akin to Old High German spuot prosperity, speed, Old English spOwan to succeed, Latin spes hope, Lithuanian speti to be in time
1 archaic : prosperity in an undertaking : SUCCESS
2 a : the act or state of moving swiftly : SWIFTNESS b : [SIZE=+1]rate of motion: as (1) : VELOCITY[/SIZE] 1, 3a (2) : the magnitude of a velocity irrespective of direction c : IMPETUS
3 : swiftness or rate of performance or action

[size=+1]According to the two above definitions SPEED and VELOCITY mean the same thing and the action thereof is also the same.[/size]
[size=+1]The ONLY variable in the discussion is acceleration which is the increase of EITHER or BOTH speed and velocity.[/size]

So either I am really dumb, can't read, the dictionary is incorrect or Isaac Asimov is incorrect (Masters in physics AND math)

Could it be that the dictionary of physics assigns different meanings to words otherwise used in the non-physics world.? Are we dealing with a different language here?
I am really puzzled by your last statement that I need to review physics when on the face of things it appears pretty cut and dried.