When comparing a force field from a point source to that from an extended source, the properties exhibit significant differences. For a point source, such as a small charged particle or a distant star, the field is radially symmetric and the strength diminishes uniformly in all directions as per the inverse-square law. The field lines emanate outward (or inward for attractive forces) in a radial pattern, and their density decreases with distance, indicating a reduction in field strength. In contrast, for an extended source, like a large charged plate or a planet, the field's distribution is more complex. The field lines may not diverge as rapidly, leading to a relatively uniform field strength over a certain region. This occurs because different parts of the extended source contribute to the field at a given point, resulting in a cumulative effect that alters the usual inverse-square law behaviour. The shape of the field lines and the rate at which the field strength decreases depend on the geometry of the extended source, making the analysis more complex than in the case of a point source.

Field lines are a vital tool in visualising and understanding force fields. They are imaginary lines drawn in a field to represent the direction of the force at various points. The direction of the field is tangential to the field lines at any point, providing a clear visual indication of how the force acts. Moreover, the density of these lines in a region indicates the strength of the field – closely spaced lines signify a strong field, while widely spaced lines indicate a weaker field. For instance, around a bar magnet, field lines emerge from the north pole and enter the south pole, illustrating the magnetic field's direction. In the case of an electric field around a charged particle, the lines radiate outward or inward depending on whether the charge is positive or negative. Field lines never cross each other, as that would imply two different directions for the force at a single point, which is physically impossible. This concept provides an intuitive understanding of how forces act in a field and how their strengths vary spatially.

Equipotential surfaces are an essential concept related to force fields, representing surfaces where the potential energy of a test particle is constant. In the context of force fields, these surfaces provide crucial information about the nature and structure of the field. Each point on an equipotential surface has the same potential energy, and therefore, no work is done when moving a test particle along this surface. The key property of equipotential surfaces is that they are always perpendicular to the field lines. This perpendicularity implies that the force field does no work on a particle moving along an equipotential surface, as the force is always at a right angle to the displacement. In gravitational fields, for example, equipotential surfaces around a spherical mass like a planet are concentric spheres. In electrostatic fields, the shapes of these surfaces can vary depending on the charge distribution. Analyzing the spacing and shape of equipotential surfaces helps in understanding the field's strength and variation. Closely spaced surfaces indicate a region of high field strength, while widely spaced surfaces suggest a weaker field.

Force fields can be shielded or blocked, but the methods and effectiveness depend on the type of field. For magnetic fields, shielding is commonly achieved using materials like iron or special alloys that have high magnetic permeability. These materials provide a path of least resistance for the magnetic field lines, effectively redirecting the field around the shielded area. This is the principle behind the shielding of electronic components from external magnetic fields. For electric fields, conductive materials are used for shielding. When a conductor is placed in an electric field, it redistributes its free electrons in such a way that it cancels the field inside, rendering the interior field-free. This is known as electrostatic shielding and is the principle behind Faraday cages, which protect sensitive equipment from external electric fields. Gravitational fields, however, cannot be shielded against in the same way. The universality of gravity and its always attractive nature make it pervasive and impossible to block using current technology and understanding of physics. Thus, while magnetic and electric fields can be effectively shielded, gravitational fields remain unalterable by such means.

The inverse-square law is a fundamental principle in physics, particularly significant in the context of force fields. It states that the strength of a field created by a point source diminishes as the square of the distance from the source. This law applies to several types of fields, most notably gravitational and electrostatic fields. For instance, the gravitational force exerted by a celestial body like the Earth or the Sun decreases with the square of the distance from the body. Similarly, the strength of the electrostatic field around a charged particle diminishes in proportion to the square of the distance from the charge. The inverse-square law reflects the dispersion of the field in three-dimensional space – as the field spreads out spherically, its intensity decreases proportionally to the area of the sphere, which increases with the square of the radius. This principle is crucial in understanding the behaviour of fields over distance and is a key element in calculating forces and potentials in various physical situations, from planetary motion to the interaction of charged particles.