Calculating Revolutions/Minute for Centrifuge at 4.62 cm Radius

  • Thread starter matchboxdude
  • Start date
  • Tags
    Centrifuge
In summary, we were discussing the use of a centrifuge and calculating the number of revolutions per minute of a sample located at a radius of 4.62 cm from the axis of rotation. After some confusion, it was determined that the correct formula to use is centripetal acceleration = (v^2)/r. Using this formula and substituting in the given values, we get an angular velocity of 1034.993778 radians per second, which can be converted to revolutions per minute by dividing by 2*pi. Another formula that can be used is f = 1/T = v/2*pi*r, which also gives the number of revolutions per second.
  • #1
matchboxdude
8
0
ok, you are using a centrifuge. the centripetal acceleration of the sample is 5.05E3 times larger than the accelleration due to gravity. how many revolutions/minute is the sample making if it is located at a radius of 4.62 cm from the axis of rotation?

i think i use: centripetal accellearion = (v^2)/r
so... 5.05E6*9.8m/s = v^2 / 4.62cm
v = 47.8167 rev/min. but i get it incorrect.. any hints?
 
Physics news on Phys.org
  • #2
Why take [itex]5.05^6[/itex] times g, instead of the given [itex]5.05^3[/itex]?

Edit: Nevermind, that was a typo, you used the correct value.

But v is the velocity, not the number of revolutions per minute.
The time it takes (in seconds) for one revolution is [tex]T=\frac{2\pi r}{v}[/tex]
 
Last edited:
  • #3
oops sorry. i meant 5.05^3 in my calculations. i used it, but just typed it here wrong.
 
  • #4
ok, in my first equation. when i have the radius, should that be 4.62cm or .0462m ? because i used .0462m even though i wrote 4.62cm
 
Last edited:
  • #5
ok, you are using a centrifuge. the centripetal acceleration of the sample is 5.05E3 times larger than the accelleration due to gravity. how many revolutions/minute is the sample making if it is located at a radius of 4.62 cm from the axis of rotation?

i think i use: centripetal accellearion = (v^2)/r
so... 5.05E6*9.8m/s = v^2 / 4.62cm
v = 47.8167 rev/min. but i get it incorrect.. any hints?
You want angular velocity, you're using the linear velocity formula!
Just use simple substitution...
r = Radius
Because v = rw (Where w is angular velocity)
Centripetal Acceleration = (rw)^2/r Which gives:
(r^2w^2)/r = rw^2
And Radius should ALWAYS be in metres, unless asked otherwise..
Just solve for w.
 
Last edited:
  • #6
so everything i did was wrong? ok.
ok so i took:
5.05E3*9.8 = .0462w^2
w=1034.993778 and is that revolution/sec?
is that better?
 
  • #7
anyone :cry:
 
  • #8
matchboxdude said:
so everything i did was wrong? ok.
ok so i took:
5.05E3*9.8 = .0462w^2
w=1034.993778 and is that revolution/sec?
is that better?
That would radians per second. You traverse [itex]2\pi[/itex] radians in one revolution, so dividing [itex]\omega[itex] by [itex]2\pi[/itex] will give the number of revolutions per second.

And no, it's not true that everything you did was wrong. You could take
[tex]f=\frac{1}{T}=\frac{v}{2\pi r}[/tex] which also gives the number of revolutions per second.
 

FAQ: Calculating Revolutions/Minute for Centrifuge at 4.62 cm Radius

How do you calculate revolutions per minute (RPM) for a centrifuge at a radius of 4.62 cm?

To calculate RPM for a centrifuge at a radius of 4.62 cm, you will need to use the formula RPM = (v/2πr) x 60, where v is the linear velocity and r is the radius. Plug in the values for v and r, and solve for RPM.

What is the linear velocity of a centrifuge with a radius of 4.62 cm?

To find the linear velocity, you can use the formula v = ωr, where ω is the angular velocity and r is the radius. If the angular velocity is not given, you can calculate it by dividing the RPM by 60 and then converting it to radians per second (ω = (RPM/60) x 2π). Once you have ω, plug it into the formula along with the radius and solve for v.

Can I use the same formula to calculate RPM for a centrifuge with a different radius?

Yes, the formula for calculating RPM for a centrifuge at a specific radius is universal and can be used for any centrifuge. Just remember to use consistent units for radius and velocity (such as cm and cm/s or m and m/s).

Is there a maximum RPM for a centrifuge at 4.62 cm radius?

The maximum RPM for a centrifuge at a specific radius depends on various factors such as the material and design of the centrifuge, as well as the sample being centrifuged. Consult the manufacturer's instructions for the specific centrifuge to determine its maximum RPM at 4.62 cm radius.

What is the purpose of calculating RPM for a centrifuge at 4.62 cm radius?

Calculating RPM for a centrifuge at 4.62 cm radius is important for determining the appropriate speed and duration for centrifugation in order to effectively separate the components of a sample. It also ensures the safety of the centrifuge and the samples being centrifuged.

Similar threads

Back
Top