Is Centripetal Acceleration Constant in Uniform Circular Motion?

[faiziqb12]

Homework Statement

i was going through uniform circular but a confusion popped out of my head .
as i have read before the Rutherford atomic model was only rejected due to
the fact that electrons moving in circular orbits need to accelerate constantly
to maintain a uniform speed but the acceleration causes electrons to radiate
the energy and they would eventually lose all their energy and fall into the
nucleus ... so my question is in uniform circular motion there is a constant
acceleration which keeps a uniform speed..is it centripretal acceleration?
how?... and how to calculate the magnitude and direction of this
acceleration? ... and is it a constant?

 

[tms]

What are your answers?

 

[faiziqb12]

What are your answers?

i am empty
i was trying to add up the the gravitation,friction and centripretal acceleration vector
but it proved of no use

 

[faiziqb12]

i have ran out of my mind
and here are no websites that can help me
please help!

 

[Qwertywerty]

so my question is in uniform circular motion there is a constant
acceleration which keeps a uniform speed..is it centripretal acceleration?
how?... and how to calculate the magnitude and direction of this
acceleration? ... and is it a constant?

What is centripetal acceleration ? What causes it ?

 

[faiziqb12]

What is centripetal acceleration ? What causes it ?

NO MY QUESTION ACTUALL IS THE SAME AS I HAVE POSTED
the centripetal force just allows a body to be fixed in a circular orbit but what causes the object to keep a fixed velocity in that circular orbit

 

[Qwertywerty]

the centripetal force just allows a body to be fixed in a circular orbit but what causes the object to keep a fixed velocity in that circular orbit

Is the velocity constant ? Does uniform circular motion maintain constant speed , or constant velocity ?

 

[faiziqb12]

Is the velocity constant ? Does uniform circular motion maintain constant speed , or constant velocity ?

oh sorry constant speed

 

[Qwertywerty]

Okay , so it is now clear that velocity of the object is changing .

Now , for constant mass systems , if velocity of object is changing , then what does that say about object's acceleration - is it zero ?

 

[faiziqb12]

Okay , so it is now clear that velocity of the object is changing .

Now , for constant mass systems , if velocity of object is changing , then what does that say about object's acceleration - is it zero ?

yes

 

[Qwertywerty]

yes

No , it isn't !

What causes change in velocity ?

 

[faiziqb12]

No , it isn't !

What causes change in velocity ?
i was talking about magnitude...
now you come on the question
i can see two types of acceleration
one that keeps the object the object in orbit{centripedal acceleration}

my question is about the second one ..that one which keeps a uniform speed or say a uniform magnitude of velocity

 

[faiziqb12]

No , it isn't !

you are right

 

[Qwertywerty]

one that keeps the object the object in orbit{centripedal acceleration}

my question is about the second one ..that one which keeps a uniform speed or say a uniform magnitude of velocity

Consider a pebble tied to a string , rotated about a fixed point . As it starts to spin , tension acts as a centripetal force , consequently causing an acceleration - which is the centripetal acceleration .

This acceleration is responsible for circular motion . For uniform circular motion , this is the pebble's only acceleration .
It causes change in velocity of the pebble . As this is perpendicular to initial velocity of pebble , it only causes a change in the pebble's direction of motion of the pebble , working like this throughout the circular motion .

Thus , my question to you is this - how is the acceleration changing the velocity ( we have already seen that velocity is changing ) ?
Also , how is velocity ( a vector ) related to speed ( a scalar ) ?

 

[faiziqb12]

This acceleration is responsible for circular motion. For uniform circular motion , this is the pebble's only acceleration .
Also , how is velocity ( a vector ) related to speed ( a scalar ) ?

THE centripetal force is only responsible for keeping the body in orbit not for increasing,decreasing or maintaining its speed.
in uniform circular motion there is constant speed due to the force applied by us repeatedly...and this force is the second type of acceleration
now my question is how can i calulate the amount of such acceleration needed to maintain uniformity of speed
i hope you would have understood my question now

 

[Qwertywerty]

Please understand , I have got your question . What my problem is that you seem to be making mistakes in your basic concepts .

So please answer these -

Thus , my question to you is this - how is the acceleration changing the velocity ( we have already seen that velocity is changing ) ?
Also , how is velocity ( a vector ) related to speed ( a scalar ) ?

 

[faiziqb12]

Please understand , I have got your question . What my problem is that you seem to be making mistakes in your basic concepts .

So please answer these -

velocity has direction along with magnitude so it is a vector and speed has only a magnitude so it is a scalar
also acceleration is changing the velocity by changing its direction

 

[Qwertywerty]

velocity has direction along with magnitude so it is a vector and speed has only a magnitude so it is a scalar
also acceleration is changing the velocity by changing its direction

So , in the entire motion , only direction of the velocity is changing , and not it's magnitude . So if it's magnitude isn't changing , speed isn't changing .

So , to finally answer your question , no acceleration is causing uniform speed . Speed was never changing , and hence no acceleration was ever required to do so .

 

[faiziqb12]

So , in the entire motion , only direction of the velocity is changing , and not it's magnitude . So if it's magnitude isn't changing , speed isn't changing .

So , to finally answer your question , no acceleration is causing uniform speed . Speed was never changing , and hence no acceleration was ever required to do so .

what you want to say is if we stop rotating the string in the example , but not let the string go.then the ball will again be in uniform motion.

no, it wont

we revolve our hands to give the desired force always to cancel the effect of gravitational force and the frictional force in the example given

and this force is actually the another accleration i was talking about

 

[Qwertywerty]

what you want to say is if we stop rotating the string in the example , but not let the string go.then the ball will again be in uniform motion.

?

How exactly would you do this ?

 

[Qwertywerty]

we revolve our hands to give the desired force always to cancel the effect of gravitational force and the frictional force in the example given

Again , what example ? What force of the hand ?

 

[faiziqb12]

the example is that a string is attached to a ball on one side and a figer on the other side
we rotate the finger that's the force of the hand

 

[faiziqb12]

According to Newton's first law of motion, it is the natural tendency of all moving objects to continue in motion in the same direction that they are moving ... unless some form of unbalanced force acts upon the object to deviate its motion from its straight-line path. Moving objects will tend to naturally travel in straight lines; an unbalanced force is only required to cause it to turn. Thus, the presence of an unbalanced force is required for objects to move in circles.
this unbalanced force is the force of the hand

 

[Qwertywerty]

According to Newton's first law of motion, it is the natural tendency of all moving objects to continue in motion in the same direction that they are moving ... unless some form of unbalanced force acts upon the object to deviate its motion from its straight-line path.

This is the centripetal force , provided by the string . Please reread the previous posts .

 

[Qwertywerty]

Edit : Do you feel your question has been answered already ?

 

[faiziqb12]

N

You seem to be stating facts ( facts - accodin to you ) . Has your question thus been answered already ?

O IT IS A QUESTION
MY QUESTION IS THAT HOW TO CALCULATE THE SECOND TYPE OF ACCELERATION BESIDES CENTRIPETAL WHICH I MENTIONED EARLIER

 

[Qwertywerty]

MY QUESTION IS THAT HOW TO CALCULATE THE SECOND TYPE OF ACCELERATION BESIDES CENTRIPETAL WHICH I MENTIONED EARLIER

There is no other acceleration of the rotating object .

 

[faiziqb12]

i said earlier that there is and also explained it

 

[Qwertywerty]

i said earlier that there is and also explained it

Edit : If an object's velocity is changing in the sense that it's direction changes but not it's magnitude , then force is not affecting the speed of the object - because magnitude of velocity isn't changing in that case , only it's direction is .

 

[tms]

If an object moves with a constant speed , there cannot be an acceleration of the body .

You mean a constant velocity.

 

[Qwertywerty]

You mean a constant velocity.

No , sorry , that's not what I meant . See my edited post .

 

[faiziqb12]

Edit : If an object's velocity is changing in the sense that it's direction changes but not it's magnitude , then force is not affecting the speed of the object - because magnitude of velocity isn't changing in that case , only it's direction is .

yes that's true but in places like planetary motion
here in the string example there is gravitation of Earth and to balance it u need a constantly applied force
thats what i am talking about

 

[Qwertywerty]

Suppose the object is kept on a table . Then , in that case , normal cancels gravitational force .
If it is a vertical circular motion , analysis is not so simple .

here in the string example there is gravitation of Earth and to balance it u need a constantly applied force
thats what i am talking about

I'm sorry , is this what you have been talking about this whole time ?

 

[faiziqb12]

maybe u still don't understand my question

 

[Qwertywerty]

Okay , could you please repeat your question ? Also state exactly what kind of circular motion the object is doing .