As seen in earlier section, the gravitational field strength
acting on an object decreases (illustrated by an increase in the
field line spacing) as the object moves further away from Earth.
This means that field strength varies with distance from the
source mass (in this case, the Earth).

The gravitational field strength, g at a particular point in free
space is defined as the gravitational force per unit mass
acting on a point mass placed at that point.

Why must it be
a “point mass”?

Point mass is physically small so that the forces acting on
different parts of the point mass are generally the same.

LO(c)

Based on Newton’s law of gravitation, the gravitational force acting on the point mass, m by the source mass, M,

$F=$

and gravitational field strength, g is the gravitational force, F per unit mass acting on the point mass, m, we may derive that the gravitational field strength.

since we know the force on object as a result of the gravitational field created by Earth is F = mg.

putting the 2 equations together, we get

$F$

$F$

giving us the expression for gravitational field field g

$g$

From left to right,

Notice the values of g changes direction left (negative) to right (positive), suggest whether g field is a vector (magnitude and direction) or scalar (only magnitude, no direction) quality.

1) Gravitational field strength, g (depicted as a magenta color curve) is a vector quantity, and it has the direction always towards the mass M.

Try varying the values of the green test mass m, does it change the value of g?

2) As shown in $g$

As depicting in the pictures above, the values of g changes according to what relationship? linear, quadratic, inverse square etc?

try your own model by keying expression to test linear = "r", quadratic = "r^2", inverse square = "1/r^2". which model seems to depict the g well enough?

3) The magnitude of the field strength , g varies according to the in inverse square law manner $$

4) All the picture are showing the (depicted as a magenta color curve) g vs r graph for a 100-kg mass :

• On the left side of the 100-kg mass, the gravitational field strength points to the right are positive g values.

• On the right side of the 100-kg mass, the gravitational field strength points to the left are negative g values. the reason is because of the adoption of the Cartesian coordinate system with positive x direction to the right.

• As r increases, magnitude of g decreases according the formula $g$

hint: try typing in expression like 6.67*100/r^2 (left) and - 6.67*100/r^2 (right) separately.

note that the model field assumes G = 6.67 instead of 6.67x10

https://dl.dropboxusercontent.com/u/44365627/lookangEJSworkspace/export/ejss_model_gravity04/gravity04_Simulation.xhtml