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Monthly Archives: February 2012

How long does it take for a ball to fall to the bottom of a cone

Definitely not a homework question here, just a game that friends and I try to play to guess how long it takes a ball to fall to the bottom of a cone.

I do not have a lot of physics experience, but I was under the impression that if we knew certain constants such as: the diameter and height of the cone, the mass of the ball, the velocity of the ball as it falls into the cone, the angle of the side of the cone, and the usual constants for gravity and friction – that we should be able to know the exact time the ball will fall to the bottom.

We should also be able to know the distance the ball travelled going around the cone before hitting the bottom.

Sadly, I am not quite able to work out how to guess either the time or distance.  Any suggestions?

Resistance and Resistivity

Simran Asked

“Two wires A and B of equal lengths,different cross-sectional areas and made of same metal a)name the property which is same for both the wires. b)name the property which is different for both the wires”

Answer:

Since both the wires are of same metal, the resistivity will be same for both whereas since the dimensions (Area of cross section here) are different, the resistance will be different

Gravity and something more

Jihin Asked:

Some Things That I Have Always Wondered OF : (i hope it may be answered soon …)
1)is it possible that our human body can withstand pressures twice or more than the atmospheric pressure without a suite or is there any artificial instruments or means in which our heart can be made to pump into a level in which we can attain this ability !!!
2)when more gravity  is experienced , it is said that time travels slowly – is it  relative ??? caz time goes at a constant rate !!! it is only the position or view that makes the observer feel the situations ???
3) Is there any gravity chambers successfully made out … in which the gravity can be changed accordingly to observe diff. phenomena ??? Cant It be possible to do that ????

Ans:

To be posted soon.

However, I agree that I may not be able to give you a satisfying answer to all your queries, as “Science says the first word of everything and the last word of nothing.” We are learning new things everyday. When we explore more and more, we find that we know less and less and our knowledge is too meagre.

By the time I prepare a well fitting answer to this, visitors are also requested to respond to the question by posting answers and comments.

Rate of change of acceleration?

What is the name for rate of change an acceleration?

(P. Selvam asked)

Answer:

The rate of change of acceleration is called Jerk or Jolt

\vec j=\frac {\mathrm{d} \vec a} {\mathrm{d}t}=\frac {\mathrm{d}^2 \vec v} {\mathrm{d}t^2}=\frac {\mathrm{d}^3 \vec r} {\mathrm{d}t^3}
Just for info:
yank (symbol Y) has been suggested for rate of change of force, tug (symbol T) for rate of change of yank, snatch (symbol S) for rate of change of tug and shake (symbol Sh) for rate of change of snatch.

Physics.org Award winning websites

http://scienceblogs.com/startswithabang/

http://www.zooniverse.org/

http://www.popsci.com/

http://www.cosmosmagazine.com/

http://www.guardian.co.uk/science/series/science

http://www.physicsforums.com/

http://www.last-word.com/index.php

http://www.nasa.gov/audience/forkids/kidsclub/flash/index.html

https://project-cernland.web.cern.ch/project-CERNland/index.html

http://www.physics.org/

http://www.sciencefairstl.org/

Scientists Agree Again – Light is the Fastest not neutrino

Year 2012 started with a struggle among the intellectuals and scientists when CERN released the finding that “Neutrinos travel faster than light

But, now the scientists of CERN suspect that it could be an error in measurement of time that caused the faulty calculation. They are blaming the loose connection in Fibre Optic Cables and the GPS signals. A GPS correction applied to the time sensor after triggering the neutrinos could have caused the error in measurement of time.

The extremely small timespan of 60 nanoseconds could easily be caused by either or both of these causes or may be some error due to other causes. However the scientists will be re-evaluating the procedure and will be repeating with apparatus equipped with more precise measuring systems.

Till then – “NOTHING TRAVELS FASTER THAN LIGHTEINSTEIN CONTINUES TO ROCK”

Form of Kepler’s in a different universe!

Mukta asked:

“imagine a planetary system in which gravitational force varied as 1/r instead of 1/r2 .what relation would correspond to KEPLER’S THIRD LAW (SQUARE OF TIME PERIOD / CUBE OF SEMI MAJOR AXIS.?”

(Answer)

If the gravitational force varied as 1/r instead of 1/r2 , then Kepler’s Law of periods would have to be modified accordingly and it would give T proportional to r.

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