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Author Topic: Ejs Open Source Gravity Field Model Near Earth Java Applet  (Read 7173 times)
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on: October 01, 2010, 08:10:28 am »

Ejs Open Source Gravity Field Model Near Earth Java Applet
trying to make a better version of this http://webphysics.davidson.edu/physlet_resources/bu_semester1/c17_field.html http://webphysics.davidson.edu/physlet_resources/bu_semester1/index.html in Ejs
thanks to Fu-Kwun Hwang for his guidance and support. http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1966.msg7283#msg7283

The Gravitational Field
A field is something that has a magnitude and a direction at every point in space. Gravity is a good example - we know there is an acceleration due to gravity of about 9.81 m/s2 down at every point in the room. Another way of saying this is that the magnitude of the Earth's gravitational field is 9.8 m/s2 down at all points in this room.

Gravitational field: g = F/m , relating to the Cartesian coordinate system, therefore, acceleration in +y direction ay = -9.81 m/s2

where F is the force of gravity.

We can draw a field-line pattern to reflect that, near the Earth's surface, the field is uniform. The strength of a field is reflected by the density of field lines - a uniform field has equally-spaced field lines. But since the visualization is arbitrary, the slider n is designed to allow for visualization different number of field lines to draw, to key is they are equally spaced but by how much is arbitrary set.
the play and reset button now allows for the applet to run to show what happens as time evolve which can be mathematical model as y = uy.t + 1/2.(-9.81).t2

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If we zoom out and view the Earth from far away, we get a non-uniform pattern. In fact, the pattern is radial - the lines are further apart as they get further from the Earth, reflecting the fact that g decreases with distance. At every point, though, the field-line pattern shows the direction of the gravitational force that would be experienced by a mass placed at that point.
But that is another applet Smiley

« Last Edit: October 04, 2011, 07:00:51 pm by lookang » Logged
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