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Torque, rotational inertia and angular acceleartion

  • Thread starter urbano
  • Start date
  • #1
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Homework Statement



In order to link these into a logical sequence, how do they fit together

Homework Equations



I = rotational inertia a = angular acceleration (I know a different symbol is usually used)
τ= force x moment arm distance

The Attempt at a Solution



so....to get my head around how these interact

Torque is the amount of rotational force applied to a body.

rotational inertia is how much the body will resist this force

angular acceleration is how dpenedne ton these two.

Situation one.

If I applied 5Nm of torque to a body that had a rotational inertia greater than this then the body wouldn't move and its angular acceleration would be 0

Situation two.

If I applied 5Nm of torque to a body that had a rotational inertia less than this then the body would move BUTwhat if it moves at a constant velocity and doesn't accelerate ? It still has 0 acceleration but is moving ?

I unsure how torque can length of moment arm x force AND moment of inertia x angular acceleration

if there is is 0 angular acceleration then moment of inertia x 0 = 0 so ther eis 0 Torque

but if I'm applying 5Nm of toruqe how can there be 0 torque ?

I must have missed something fundamental somewhere
 

Answers and Replies

  • #2
SteamKing
Staff Emeritus
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Homework Helper
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Yeah, it's called units. Look up the units of rotational inertia and angular acceleration.

BTW, applying a torque to a rotating body always acts to change the angular velocity. If the body is rotating at a constant angular velocity, what must the net torque be on the system?

Hint: Angular motion has formulas analogous to those of rectilinear motion.
 
  • #3
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BTW, applying a torque to a rotating body always acts to change the angular velocity.
.
what happens though if the body isn't rotating and I want to start it rotating but can't apply enough force to do so ? I'm still applying torque though ....aren't I ?
 
  • #4
SteamKing
Staff Emeritus
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Yes, you are. How quickly it starts to rotate depends on the amount of torque you apply and what the inertia of the body is.
 
  • #5
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what happens though if the body isn't rotating and I want to start it rotating but can't apply enough force to do so ? I'm still applying torque though ....aren't I ?
like SteamKing said, yes you are. But the net torque is zero, hence it doesn't rotate or simply some other torque resists the torque you are applying.
 

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