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Physics Circular motion

I dont seem to understand how angular velocity and frequency are related, and i dont even really understand what angular velocity is. Anyone care to explain? thank you! :smile:
angular velocity is just the rate of change of angle, the unit is usually radians per second which can be compared to the unit of linear velocity which is meters per second.

e.g. a hard disk platter is spinning at 3600 rpm
which is 60 revolutions per second
1 revolution is an angle of 2π radians
so it's angular velocity is 120π radian per second

---
frequency is the number of revolutions (or cycles) per second... and each cycle is 2π radians
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brainmatter
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Original post by Joinedup
angular velocity is just the rate of change of angle, the unit is usually radians per second which can be compared to the unit of linear velocity which is meters per second.

e.g. a hard disk platter is spinning at 3600 rpm
which is 60 revolutions per second
1 revolution is an angle of 2π radians
so it's angular velocity is 120π radian per second

---
frequency is the number of revolutions (or cycles) per second... and each cycle is 2π radians



Thank you! this is really helpful, but i still dont understand where omega comes in? and how to derive w=2 x pi x f?
Original post by brainmatter
Thank you! this is really helpful, but i still dont understand where omega comes in? and how to derive w=2 x pi x f?


lower case omega is just the usual symbol for angular velocity.- the equivalent of u and v for linear velocity in the SUVAT

frequency is cycles per second
angular velocity is radians per second
there are 2π radians in every cycle

so if you want to convert a number of cycles to a number of radians you multiply by 2π
Reply 4
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brainmatter
OP
3
Original post by Joinedup
lower case omega is just the usual symbol for angular velocity.- the equivalent of u and v for linear velocity in the SUVAT

frequency is cycles per second
angular velocity is radians per second
there are 2π radians in every cycle

so if you want to convert a number of cycles to a number of radians you multiply by 2π


Thank you! another question...when you need to eject a mass from a satellite in order to increase or decrease the acceleration, how do you know which direction the mass should be ejected?
Original post by brainmatter
Thank you! another question...when you need to eject a mass from a satellite in order to increase or decrease the acceleration, how do you know which direction the mass should be ejected?


You get a reaction force in the opposite direction same as firing a rocket...

on orbiting satellites maneuvering is a bit complicated because you don't just move around in straight lines. e.g. if you wanted to dock with a space station in circular orbit at 450km altitude and you were orbiting at 400km you'd fire your rockets or eject your masses backwards wrt your orbital velocity until you were also orbiting at 450km - if you pointed your nose at the space station and fired your rocket you'd make your orbit elliptical and trying to dock things in different shaped orbits is a lot more difficult. When it's time to go home you'd point your nose backward wrt your orbital velocity and fire your rocket to go into a lower altitude orbit.

I guess at A level you're either going to be firing your mass forward or backward wrt your orbital velocity in order to keep the orbits circular and obeying the circular motion laws.

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