Physics questions

[TrueTears]

velocity isnt constant. The direction changes. The magnitude of velocity (Speed) is constant.

but didnt appianway just say "Uniform circular motion refers to orbiting at a constant radius at a constant velocity"....?

[appianway]

Oh sorry, I meant to write speed.

... I can't believe I wrote a whole thing about how speed =/= velocity and then said it essentially was ==

[TrueTears]

oh okay thanks heaps guys

what about the graph and non uniform circular motion questions, any help on those?  

what is angular velocity? i know its

but what does it mean? say i got a graph and its like the one attached, how do u describe the motion of the particle?

also for non uniform circular motion the acceleration doesn't point towards the centre of circular anymore right?

whats radial acceleration and tangential acceleration? i understand the magnitude of the acceleration in non uniform circular motion is given by , but where did this radial acceleration and tangential thingy pop up from?

thanks ^_^

[TrueTears]

also i dont get the last 2 diagrams on the diagram attached, how is the sign of the angular acceleration determined? why is it a>0 for the 2nd last one and a<0 for the last one?

thanks

[kamil9876]

It's really an analogous question to the very first one of this thread. Just imagine as a quantity that is like position, as velocity and angular acceleration as acceleration.

for the third one: is decreasing(slowing down) but it is negative. so its like the sequence -5,-4,-3... (an increasing sequence), and thus a>0.

[TrueTears]

ahhh i see, so these rotational kinematics is similar to the linear kinematics?

[kamil9876]

It's just because of calculus really: if  |dx/dt| is decreasing but negative, then is increasing and thus is positive. So the similairity is just a mathematical consequence of the fact that the definitions are basically the same. (x can be angle, displacement, electric charge... whatever)

[TrueTears]

pls dont confuse me even more, dont bring calculus in here with physics, i dont care if theyre related, i just remember the formulas coz i am not interested in the deviations.

[TrueTears]

how to do this question? no idea...

[kamil9876]

pls dont confuse me even more, dont bring calculus in here with physics, i dont care if theyre related, i just remember the formulas coz i am not interested in the deviations.

you asked for it, this understanding is helpful for all applications.

As for the question:

convert to revs per second.

Assuming it is uniformly slowing down. (constant acceleration) then:

 (see, another consequence of my suggestion in the pervious post)

And so because is in seconds, are in revs per sec(after converting), then is the angle measured in revs, just as you want it.

[TrueTears]

you can use those equations for circular motion? i neva knew dat =S

[kamil9876]

Yes, because they are just consequences of calculus.

[TrueTears]

ahhh sik sik, thanks man!!

[TrueTears]

whats kinetic friction and static friction?

in my book it says kinetic friction is a force that opposes motion and static friction is a force that points in the direction that prevents motion.

wdf isn't that the same thing?

can anyone show me an example where it clearly isnt the same thing?

[kamil9876]

STATIC(literally, still...motionless) friction: motion is NOT occuring, being prevented by the static friction.


KINETIC(literally, in motion) friction: motion is occuring but the magnitude of it is lessened by the kinetic friction.