Define the field as action at a distance. Discuss that objects within the gravitational field feel a force of attraction. Sketch how the field is strongest closer to the object, such as the Earth, and the force field spreads as distance increases. The field decreases as the square of the distance. The field is zero at the center of the Earth, no net force. Elicit why a scale placed in an elevator which is free falling down will show a weight of zero, feels like no gravity. There is no supporting force to push up.