# 0.32 Phy1320: angular momentum -- the mathematics of torque  (Page 7/13)

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Similar to Newton's second law

This equation is Newton's second law applied to a system of particles in rotation about a given axis. It makes no assumptions about constant rotationalvelocity.

## Torque from an anecdotal viewpoint

One of the objectives of this module is to develop concepts involving rotational motion that are analogous to concepts from earlier modules that involve translationalmotion.

A Lazy Susan

On my dining room table, there is a device that is commonly called a Lazy Susan. In case you are unfamiliar with such devices, it is essentially aturntable. By a turntable, I mean a rather large disk mounted on bearings so that it is free to turn in a plane that is slightly above but parallel with thetop of the dining room table.

The purpose of the Lazy Susan

The purpose of a Lazy Susan is to make it easier to serve food at the dining room table. Various dishes are placed on it . When someone wants a helping ofcarrots, for example, instead of saying "Please pass the carrots," they simply turn the Lazy Susan until they can reach the bowl of carrots and helpthemselves.

However, we won't be discussing how to serve carrots in this module. In this module, I will use the Lazy Susan, in its empty state between meals, to discussvarious aspects of rotating rigid objects.

To make it easier to type the material under discussion, I will refer to the Lazy Susan as a turntable. (For some reason, I can type turntable much morequickly than I can type Lazy Susan.)

Low angular acceleration when coasting

My turntable has pretty good bearings. It is also rather heavy for its size and therefore has a relatively large rotational inertia or moment of inertia, whichever term youprefer.

If you give it a good spin, it will spin for quite a while before all of its rotational energy is dissipated through friction in the bearings and airresistance. By default, therefore, its angular acceleration is low. In other words, the rate of change of its angular velocity is small.

A perpetual motion machine

If we could find a way to eliminate all of the frictional forces acting on the turntable, including air resistance, then it would spin forever. In thatcase, we would have invented what has been called a perpetual motion machine. Therate of change of angular velocity would be zero, meaning that its angular acceleration would also be zero.

Similar to Newton's first law

This reminds us of a moving body that satisfies Newton's first law, which can be paraphrased something like the following:

• a body in motion, being acted upon by no net forces, will continue moving forever in a straight line.

In other words, that law tells us that absent a force to the contrary, a moving body will continue tomove with no change in velocity.

If we could eliminate all of the frictional forces acting on my turntable (which is a rotating body), we might like to say that

• absent any net forces acting on the body, a rotating body with a constant rotational inertia willcontinue rotating with the same angular velocity forever.

Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
how did you get the value of 2000N.What calculations are needed to arrive at it
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