# Breakdown of Circular Motion

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Hi,

Is my understanding right that when centripetal force is less than m*r*omega^2, the particle takes off at a tangent where as when the centripetal force is greater than m*r*omega^2, the particle moves in projectile motion. I am talking in the context of a string strictly, not a rod.

Is my understanding right that when centripetal force is less than m*r*omega^2, the particle takes off at a tangent where as when the centripetal force is greater than m*r*omega^2, the particle moves in projectile motion. I am talking in the context of a string strictly, not a rod.

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#2

(Original post by

Hi,

Is my understanding right that when centripetal force is less than m*r*omega^2, the particle takes off at a tangent where as when the centripetal force is greater than m*r*omega^2, the particle moves in projectile motion. I am talking in the context of a string strictly, not a rod.

**Tesla3**)Hi,

Is my understanding right that when centripetal force is less than m*r*omega^2, the particle takes off at a tangent where as when the centripetal force is greater than m*r*omega^2, the particle moves in projectile motion. I am talking in the context of a string strictly, not a rod.

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(Original post by

what is generating the force, the tension in the string?

**mqb2766**)what is generating the force, the tension in the string?

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#4

(Original post by

Tension and at some points components of weight are effecting the motion as well.

**Tesla3**)Tension and at some points components of weight are effecting the motion as well.

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(Original post by

Ok, can you be a bit more specific. In the horizontal plane so no gravity etc or .... It helps tp give a clear answer.

**mqb2766**)Ok, can you be a bit more specific. In the horizontal plane so no gravity etc or .... It helps tp give a clear answer.

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#6

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Well, its a vertical circle so gravity is playing some role.............

**Tesla3**)Well, its a vertical circle so gravity is playing some role.............

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(Original post by

It does, but only if you say its vertical motion. So what is the force equation perpendicular to the tangent (along the string)? If you have circular motion, the tension is the difference between centripetal and gravity. If the string snaps, there is a parabolic motion of a projectile under gravity. if the tension goes to zero (and then negative so you don't have circular motion), its again parabolic as the string plays no role hence the circular/centripetal effect does not apply.

**mqb2766**)It does, but only if you say its vertical motion. So what is the force equation perpendicular to the tangent (along the string)? If you have circular motion, the tension is the difference between centripetal and gravity. If the string snaps, there is a parabolic motion of a projectile under gravity. if the tension goes to zero (and then negative so you don't have circular motion), its again parabolic as the string plays no role hence the circular/centripetal effect does not apply.

m*g*sin(theta) = m*r*(d^2theta/dt^2)

Also what do you mean by the fact that tension is the difference between centripetal and gravity. Just don't get what you are saying....

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#8

(Original post by

The force equation perpendicular to the tangent is :

m*g*sin(theta) = m*r*(d^2theta/dt^2)

Also what do you mean by the fact that tension is the difference between centripetal and gravity. Just don't get what you are saying....

**Tesla3**)The force equation perpendicular to the tangent is :

m*g*sin(theta) = m*r*(d^2theta/dt^2)

Also what do you mean by the fact that tension is the difference between centripetal and gravity. Just don't get what you are saying....

http://hyperphysics.phy-astr.gsu.edu...s/cirvert.html

Is pretty good.

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#9

Let's look at two examples: one horizontal and one vertical.

Take a mass, attatched to a string of length orbiting with angular frequency .

Horizontal:

We know when the string snaps the mass will move off tangentially.

Vertical:

Consider the forces acting on the mass at the top of the circle, where is the tension in the string.

If the string is to remain taught, thus able to deliver force, we need .

If the string loses tension the mass will move as a parabola as the only force acting is gravity.

Now consider the forces acting on the mass at the bottom of the circle, so .

If this is greater than the maximium tension the string can tolerate, the mass will undergo parabolic motion as the only force acting is gravity.

Take a mass, attatched to a string of length orbiting with angular frequency .

Horizontal:

We know when the string snaps the mass will move off tangentially.

Vertical:

Consider the forces acting on the mass at the top of the circle, where is the tension in the string.

If the string is to remain taught, thus able to deliver force, we need .

If the string loses tension the mass will move as a parabola as the only force acting is gravity.

Now consider the forces acting on the mass at the bottom of the circle, so .

If this is greater than the maximium tension the string can tolerate, the mass will undergo parabolic motion as the only force acting is gravity.

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(Original post by

Where is the tension in that equatiion?

http://hyperphysics.phy-astr.gsu.edu...s/cirvert.html

Is pretty good.

**mqb2766**)Where is the tension in that equatiion?

http://hyperphysics.phy-astr.gsu.edu...s/cirvert.html

Is pretty good.

T - mgcos(theta) = m*r*omega^2

and the force equation parallel to tangent is:

mgsin(theta) = m*r*(d^2theta/dt^2)

Also when you say that " If you have circular motion, the tension is the difference between centripetal and gravity. " Do you mean to say motion under gravity and motion under centripetal force (i.e. circular motion).

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(Original post by

Let's look at two examples: one horizontal and one vertical.

Take a mass, attatched to a string of length orbiting with angular frequency .

Horizontal:

We know when the string snaps the mass will move off tangentially.

Vertical:

Consider the forces acting on the mass at the top of the circle, where is the tension in the string.

If the string is to remain taught, thus able to deliver force, we need .

If the string loses tension the mass will move as a parabola as the only force acting is gravity.

Now consider the forces acting on the mass at the bottom of the circle, so .

If this is greater than the maximium tension the string can tolerate, the mass will undergo parabolic motion as the only force acting is gravity.

**anon2.718**)Let's look at two examples: one horizontal and one vertical.

Take a mass, attatched to a string of length orbiting with angular frequency .

Horizontal:

We know when the string snaps the mass will move off tangentially.

Vertical:

Consider the forces acting on the mass at the top of the circle, where is the tension in the string.

If the string is to remain taught, thus able to deliver force, we need .

If the string loses tension the mass will move as a parabola as the only force acting is gravity.

Now consider the forces acting on the mass at the bottom of the circle, so .

If this is greater than the maximium tension the string can tolerate, the mass will undergo parabolic motion as the only force acting is gravity.

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#12

(Original post by

oh sorry the force equation perpendicular to tangent is:

T - mgcos(theta) = m*r*omega^2

and the force equation parallel to tangent is:

mgsin(theta) = m*r*(d^2theta/dt^2)

Also when you say that " If you have circular motion, the tension is the difference between centripetal and gravity. " Do you mean to say motion under gravity and motion under centripetal force (i.e. circular motion).

**Tesla3**)oh sorry the force equation perpendicular to tangent is:

T - mgcos(theta) = m*r*omega^2

and the force equation parallel to tangent is:

mgsin(theta) = m*r*(d^2theta/dt^2)

Also when you say that " If you have circular motion, the tension is the difference between centripetal and gravity. " Do you mean to say motion under gravity and motion under centripetal force (i.e. circular motion).

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#13

(Original post by

In vertical motion, wouldn't the force be T - mgsin(theta) = m*r*omega^2 ?

**Tesla3**)In vertical motion, wouldn't the force be T - mgsin(theta) = m*r*omega^2 ?

And I said to consider at the top and bottom of the circle.

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(Original post by

Tension is the sum / difference of centripetal and resolved gravity. If its too large the string breaks. If it goes to zero, the string goes slack. In both cases you then have parabolic (quadratic - suvat) motion.

**mqb2766**)Tension is the sum / difference of centripetal and resolved gravity. If its too large the string breaks. If it goes to zero, the string goes slack. In both cases you then have parabolic (quadratic - suvat) motion.

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#15

(Original post by

I thought that when the string breaks in vertical motion, i.e. when centripetal acceleration is less than m*r*omega^2, the particle flies of at a tangent.

**Tesla3**)I thought that when the string breaks in vertical motion, i.e. when centripetal acceleration is less than m*r*omega^2, the particle flies of at a tangent.

The particle does fly off at a tangent, but this is the initial condition for parabolic motion.

Last edited by mqb2766; 3 months ago

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(Original post by

You have to consider when T<=0 or the string breaks.When positive (and not too large), the strings tension is equal to the sum / difference of centripetal & gravity and circular motion will happen.

The particle does fly off at a tangent, but this is the initial condition for parabolic motion.

**mqb2766**)You have to consider when T<=0 or the string breaks.When positive (and not too large), the strings tension is equal to the sum / difference of centripetal & gravity and circular motion will happen.

The particle does fly off at a tangent, but this is the initial condition for parabolic motion.

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#17

(Original post by

what happens when the string breaks?

**Tesla3**)what happens when the string breaks?

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(Original post by

Please define theta before throwing it out lol

And I said to consider at the top and bottom of the circle.

**anon2.718**)Please define theta before throwing it out lol

And I said to consider at the top and bottom of the circle.

Btw when you say that " If the string is to remain taught, thus able to deliver force, we need T > 0 (i.e. m*r*omega^2 - mg > 0 " .

Shouldn't it be T > 0 (i.e. m*r*omega^2 - mgcos(theta) > 0 ) ?

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(Original post by

Parabolic or suvat motion under gravity.

**mqb2766**)Parabolic or suvat motion under gravity.

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#20

(Original post by

Shouldn't it be T > 0 (i.e. m*r*omega^2 - mgcos(theta) > 0 ) ?

**Tesla3**)Shouldn't it be T > 0 (i.e. m*r*omega^2 - mgcos(theta) > 0 ) ?

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