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Where does the potential energy come from

That raises another issue. What happens to the clock when the spring or weights expend all of their stored energy. The answer is that eventually the pendulum will stopswinging and the clock will stop running unless a human imparts more energy intothe spring or weight system that keeps the clock running.

Twenty-four hours of controlled energy transfers

I can still remember my grandfather winding the spring on his pendulum clock as the last thing he did before going to bed each night. He was convertingpotential energy derived from food into elastic potential energy in the clock's spring.

During the next 24 hours, that elastic potential energy would be converted to a combination of gravitational potential energy and kinetic energy in thependulum, which would move the hands on the clock to indicate the correct time.

The next night, my grandfather would start the process all over again by imparting energy into the clock's spring.

Sample calculations

I will present and explain sample calculations involving both kinetic energy and mechanical energy in this section.

Kinetic energy

A roller coaster car

What is the kinetic energy possessed by a 1378 pound roller coaster car that is moving with a speed of 60 ft/sec?


Enter the following expression into the Google search box:

0.5*1378lb * (60ft/s)^2

The resulting kinetic energy is 1.045 * 10^5 joules.

Similarly, you could enter the following into the Google search box:

0.5*625kg * (60ft/s)^2

and you would get the same answer of 1.045 * 10^5 joules.

As you can see, it doesn't matter whether you use English units or SI units for mass and velocity,as long as you do the calculation correctly. The answer is the same, because the kinetic energy of the object doesn't change just because you express thosequantities in different units.

More on the roller coaster car

What would be the kinetic energy of another car with the same mass but with three times the speed?


We don't even need to evaluate the equation to answer this question. We know that the kinetic energy varies as the square of the speed, so if we triple thespeed, we will increase the kinetic energy by a factor of 3*3=9. Therefore,

KE = 9*1.045 * 10^5 joules = 9.405 * 10^5 joules

Dead Fred the daredevil

Dead Fred, the daredevil possessed a kinetic energy of 18000 joules just prior to hitting a solid brick wall on his motorcycle. If his mass was 176 pounds, what was his speed?


KE = 0.5*m*v^2, or

v^2 = KE/(0.5*m), or

v = sqrt(KE/(0.5*m)), or

v = sqrt(18000joules/(0.5*176pound))

Enter the right-hand expression above into the Google search box and you should get a velocity of

v = 21.24 m/s

Mechanical energy

A dart gun

A dart with a mass of 0.1 kg leaves the muzzle of a dart gun with a velocity of 10 m/s. The child is holding the dart gun at a position that is 1 m above theground. At that instant,

  1. What is the potential energy of the dart?
  2. What is the kinetic energy of the dart?
  3. What is the total mechanical energy of the dart?
  4. Assuming no losses of energy due to friction or other causes, what is the change in the total mechanical energy of the gun at the instant the dart exits the gun?

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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.
what is the actual application of fullerenes nowadays?
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.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket 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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