# 0.28 Phy1250: circular motion -- acceleration and centripetal force  (Page 5/6)

 Page 5 / 6

## 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.

how can chip be made from sand
is this allso about nanoscale material
Almas
are nano particles real
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
no can't
Lohitha
where is the latest information on a no technology how can I find it
William
currently
William
where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Got questions? Join the online conversation and get instant answers!