Two charges hang from pendulums whose supports can
be moved closer or further apart by an external agent.
The charges have opposite signs, and therefore attract.
An external agent moves the supports (from which the
two charges are suspended) together. The force of gravity
is pulling the charges down, and the force of electrostatic
attraction is pulling them together on the radial line
joining them. The behavior of the electric fields in
this situation is an example of an electrostatic tension
transmitted parallel to the field. That tension tries
to pull the two charges together in this situation.