Monday, August 18, 2008

1st common force: Gravitation

Gravitation

You may already know that the weight of an object depends on its location in a specific gravitational field. Your weight is not the same on earth as it is on the moon. "Weight" is a force acting on an object because the force is in a gravitational field which pulls the object towards its center.

Since "weight" is a force, it's expressed in "N". It has a point in which the force starts, a direction (from the center of gravity from the object, to the center of gravity of the earth), and a size.

This size can easily be measured with the formula:

FG=m.g (or F=m.a *)

Here, "FG" is the force of the gravitational force, m is the mass of an object (while the weight of an object depends on its place, its mass (in kg) stays constant), and "g" is the gravitational constant, which is (on sea level) 9,81 N/kg.

So, a bag of 10 kg, on sea level, is pulled towards the center of the earth by a force of 10kg.9,81N/kg=98,1N.

* Some schools start by teaching "acceleration". When an object falls in free fall (on sea level), it accelerates with 9,81m/s². And, according to Isaac Newton's definition of force, a N is the force that accelerates a mass of one kg by 1 m/s². But I thought it would be easyer just to say:

g=9,81N/kg
In stead of
a=9,81m/s²

and then having to convert kg.m/s² at the end.
So, i'll be using "g".

So, that's gravitation. I'll add more on gravitation fields in the future, but meanwhile, this should do.
The next toppic will be buoyancy




1 comment:

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The only thing I would like to see here is such photo or even two :)
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