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# Tag Archives: speed

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## Does gravity travel instantaneously?

Does gravity travels instantaneously? Or it travels equal to the speed of light.

No clear answer now. If we believe in the Theory of relativity, Gravity (Gravitational Waves travel with the same speed as that of light in vacuum. If gravitons are like photons, then it makes sense too.

However I invite you to think more and post your thoughts as comments here. Let the discussion begin.

I found the following links to know more

• http://metaresearch.org/cosmology/speed_of_gravity.asp
• http://en.wikipedia.org/wiki/Speed_of_gravity
• http://www.desy.de/user/projects/Physics/Relativity/GR/grav_speed.html

## Speed of sound

Why sound travels faster in humid air than normal air as humid air is denser than normal air? (Akash asked)

The speed of sound in a medium is inversely proportional to the square root of its density. Humid air is less dense than dry air. Therefore the speed of sounf in humid air is greater than that in dry air.

Confused?

Are you thinking why dry air is more than that of humid air? This is a common misconception. Students used to think that humid air is denser than dry air. But it is not so. Just like skimmed milk (milk removed off its cream) is more dense than normal milk (with cream). Density of cream is much less than that of the rest of milk. So when it is removed, the residual milk becomes denser.

Humid air contains water vapor content. Water vapor is lighter than air. So when air contains water vapor, its density is less. When the water content is removed, it becomes denser.

For more details refer:

## What would happen if the Earth stopped rotating?

The speed of an object on earth’s surface near equator is approximately is 1670 kilometers/hour. So, if the earth stops rotating suddenly,  the objects on the surface of earth which are unbound will be thrown eastwards tangentially with the speed of rotation of earth.

## Kinetic Energy – Numerical Problem

a running man has half the kinetic energy that a boy of half his mass has.the man speed up by 1m/s and then has the same kinetic energy as the body. what were the original speeds of man and boy?

## A Numerical Problem from Kinematics

A car starts motion from rest at uniform acceleration of 2m/sec 2 for 3 seconds, and then it maintains a constant speed for 2 seconds.Then the breaks are used to decelerate the car uniformly to rest during a time of 3 seconds.

Draw the graph representing the journey of the car then calculate

1)the maximum speed in km/sec
2)the total displacement covered

(Ahmed sent this problem)  