At the end of Phys 211 we studied the gravitational force between
two objects
F_{G,1 \; on \; 2} = F_{G,2 \; on \; 1} = \frac{Gm_1m_2}{r^2}
.The forces are directed along the straight line joining the two
objects.
This is Newton's universal theory of gravity and the fundamental constant of
Nature that determines the strength of the gravitational interaction is called
the gravitational constant.
G= 6.67\times10^{-11} \; N \; m^2/kg^2
Most of the time in Phys 211, we were solving problems on the surface of the
Earth where the force of gravity between the object and the Earth was take
to be approximately F_G = mg
. This is really the same
as the equation above with the mass of the second object set to be the mass
of the Earth and the distance between the two objects to be set at the
radius of the Earth.
The gravitational acceleration on the surface of the Earth is determined by
the mass of the Earth M_E
and the radius of the Earth r_E
such that
g= \frac{GM_E}{r_E^2} \approx 9.80 \; m/s^2
As we will see the electric force has a very analogous form to the
gravitational force.
The complexity of the problems will increase though because
-
we will deal with situations where they are many more than two objects
interacting.
- the force can be attractive and repulsive.