Gravitational potential — common mistakes

Always remember the negative sign in the gravitational potential and potential energy formulas! Forgetting it is a common mistake and will cost you marks. Also, ensure 'r' is the distance from the centre of the mass, not just its surface or the altitude.

Gravitational field strength is a vector quantity (force per unit mass) representing the force experienced by a mass at a point. Gravitational potential is a scalar quantity (work done per unit mass) representing the potential energy a unit mass would have at that point. Field strength is the negative gradient of the potential (g = -Δφ/Δr).

Defining potential as zero at infinity provides a convenient and universal reference point. It means any work done to move a mass from infinity to a finite point can be measured relative to a known zero, simplifying calculations and comparisons.

The negative sign indicates that a mass is 'bound' within the gravitational field. Energy must be supplied (positive work done by an external agent) to move the mass away from the central body and out to infinity, where its potential energy would become zero.