The physics
A dipole is +q and −q a distance d apart. Its moment p = qd points from − to +.
In a uniform field the two pushes are equal and opposite. There is no net force, but they twist the dipole.
τ = p × E, |τ| = p E sin θ U = −p E cos θ
Turned a little from the field, a dipole swings like a pendulum.
ω = √(p E / I) T = 2π / ω
With no net force, the centre of mass stays still. The dipole spins about it.
In a field that changes with distance, the end in the stronger field wins. A dipole lined up with a point charge's field moves toward the charge.
F = p dE/dr = 2kQp / r³
A big sheet gives the same field σ/2ε₀ at every distance. Outside a charged ball, the field is kQ/r² from its centre.