How many revolutions will a centrifuge rotor make before coming to rest?

In summary, the conversation discusses the calculation of the number of revolutions a centrifuge rotor will make before coming to rest, given its mass, frictional torque, and initial angular velocity. The conversation also includes a question about whether the discrepancy in the calculated value is due to a physics or math error, and the solution is provided by converting the initial angular velocity from rpm to rad/sec.
  • #1
Newton=boss
12
0
1.A centrifuge rotor rotating at 5000 rpm is shut off and is eventually brought uniformly to rest by a frictional torque of 1.60 m·N. If the mass of the rotor is 4.70 kg and it can be approximated as a solid cylinder of radius 0.0780 m, through how many revolutions will the rotor turn before coming to rest?



2. Homework Equations Change rpms to rad/sec, Theta = Omega (initial)*time + 1/2*alpha*(t^2).. alpha*1/2*MR^2= Torque



3. I get 1950 revolutions once i switch back to revolutions by mult by 180/pi..

Is it my physics or my math? help please!
 
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  • #2
Can you show your work so we can find the problem?
 
  • #3
1.6=1/2(4.7)(0.078)^2*alpha
alpha=111.908 rad/sec^2..this is a negative quantity

Omega initial=5000 rpm *pi/180=87.266 rad/sec

Omega final=0= 87.266^2 +2(-111.908)(Theta)

Theta= 34.02 rad*180/pi = 1949.51 revolutions
 
  • #4
I don't know where I am wrong..
 
  • #5
Newton=boss said:
1.6=1/2(4.7)(0.078)^2*alpha
alpha=111.908 rad/sec^2..this is a negative quantity

Omega initial=5000 rpm *pi/180=87.266 rad/sec

That is not how you convert from rpm to rad/sec. rpm means revolutions per second. How many radians is in a revolution? How about seconds in a minute? Make the appropriate conversion using those values.
 
  • #6
ah! thankyou
 

1. What is a centrifuge and how does it work?

A centrifuge is a laboratory instrument that uses centrifugal force to separate substances of different densities. It works by spinning a sample at high speeds, causing heavier particles to move towards the outside and lighter particles to stay closer to the center.

2. What is the purpose of using a centrifuge in scientific experiments?

The main purpose of using a centrifuge is to separate substances that have different densities, such as liquids and solids. It is commonly used in chemistry, biology, and medical research to isolate and purify substances for further analysis.

3. What are the different types of centrifuges?

There are various types of centrifuges, including fixed angle, swinging bucket, ultracentrifuge, and microcentrifuge. Fixed angle and swinging bucket centrifuges are commonly used for routine laboratory experiments, while ultracentrifuges are used for more specialized and sensitive applications.

4. How do you choose the appropriate centrifuge for a specific experiment?

The type of centrifuge chosen for a specific experiment depends on the sample size, speed and g-force required, and the type of separation needed. It is important to consult the manufacturer's guidelines and experiment requirements when selecting a centrifuge.

5. What are the safety precautions when using a centrifuge?

Centrifuges operate at high speeds and can be dangerous if not used properly. Some safety precautions to follow include wearing appropriate protective gear, ensuring the centrifuge is properly balanced, and avoiding opening the lid while it is in motion. It is also important to follow proper maintenance and cleaning procedures to prevent accidents.

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