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Water in a bucket

If you don't mind taking a chance on getting wet, fill a small bucket about half full of water. Then swing the bucket rapidly in a circle in a vertical plane.

If you can swing the bucket fast enough, the water will stay in the bucket even when the bucket is upside down. Why is that? The water molecules want tomove in a straight line. However, the inside surface of the bucket exerts a centripetal force on the water molecules causing them to accelerate toward thecenter of the circle. The centripetal force increases with the speed of the bucket. As long as the centripetal force is greater than the weight of thewater, the water won't fall out of the bucket onto your head. However, if you allow the speed of the bucket to decrease, you will reach the point wheregravity will overcome, and you will probably get wet.

The moon and the Earth

Don't ask me how it got started in the first place, but somehow the moon got started circling the Earth.

The speed of the moon and the radius of its orbit is just exactly right so that the gravitational force that the Earth exerts on the moon causes the moonto accelerate towards the Earth. The amount of acceleration toward the earth, when combined with the speed of the moon, causes the moon to move in a uniformcircular orbit around the Earth instead of either flying off into space or crashing into the Earth.

The work-energy explanation

It is probably time to start explaining this phenomena in a more technical and less anecdotal manner.

The application of a centripetal force for uniform circular motion causes the direction of the object to be changed without changing its speed. Let's see if we can explain this froma work-energy viewpoint.

Work

Recall from an earlier module that work is a force acting upon an object to cause a displacement . Also recall that the amount of work done on an object, expressed in Joules, is given by

Work = F * D * cosine(theta)

where

  • F represents the force that causes the displacement expressed in Newtons.
  • D represents the amount of the displacement expressed in meters.
  • theta is the angle between the direction of the displacement and the line of action of the force.

Centripetal force points toward center of circle

As we showed (or claimed to show) earlier, the centripetal force for an object in uniform circular motion always points in the direction of the center of the circle. At the sametime, the velocity vector, which represents the direction of the displacement is tangential to the circle. Therefore, the angle between the centripetal force andthe direction of displacement is 90 degrees. This means that the centripetal force does no work on the object, because the cosine of 90 degrees is zero.

No work is done

When no work is done upon an object by external forces, the total mechanical energy, consisting of potential energy plus kinetic energy, of the objectremains constant. If an object is moving in a circle in a plane that is parallel to the surface of the Earth, the effect of gravity may pull the entire planetoward the surface of the Earth, but it won't effect the circular motion unequally with respect to the position of the object in the circle.

Questions & Answers

Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
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
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
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
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
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.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Accessible physics concepts for blind students. OpenStax CNX. Oct 02, 2015 Download for free at https://legacy.cnx.org/content/col11294/1.36
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