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Fields and consequences - Coggle Diagram
Fields and consequences
Fields
A force field is an area in which an object experiences a non-contact force. Force fields can be represented as vectors, which describe the direction of the force that would be exerted on the object, from this knowledge you can deduce the direction of the field. They can also be represented as diagrams containing field lines, the distance between field lines represents the strength of the force exerted by the field in that region.
Force fields are formed during the interaction of masses, static charge or moving charges.
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In gravitational fields, the force exerted is always attractive, while in electric fields the force can be either repulsive or attractive.
Electric force acts on charge, while gravitational force acts on mass.
Grav fields
Newtons law
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Newton's law of gravitation shows that the magnitude of the gravitational force between two masses is directly proportional to the product of the masses, and is inversely proportional to the square of the distance between them, (where the distance is measured between the two centres of the masses).
Grav field strength
There are two types of gravitational field; a uniform field or radial field. These can be represented as the following field lines:
The arrows on the field lines show the direction that a force acts on a mass. A uniform field exerts the same gravitational force on a mass everywhere in the field, as shown by the parallel and equally spaced field lines. In a radial field the force exerted depends on the position of the object in the field, e.g in the diagram above, as an object moves further away from the centre, the magnitude of the force would decrease because the distance between the field lines increases.
The Earth's gravitational field is radial, however very close to the surface it is almost completely uniform.
Gravitational field strength (g) is the force per unit mass exerted by a gravitational field on an object. This value is constant in a uniform field, but varies in a radial field. There are two formulas you can use to calculate this; the first is general, while the second is used only for radial fields:
Grav potential
Gravitational potential (V) at a point is the work done per unit mass against gravitational force to move an object from infinity to a given point. Gravitational potential at infinity is zero, and as an object moves from infinity to a point, energy is released as the gravitational potential energy is reduced, therefore gravitational potential is always negative.
The gravitational potential difference(AV) is the energy needed to move a unit mass between two points and therefore can be used to find the work done when moving an object in a gravitational field.
Equipotential surfaces are surfaces which are created through joining points of equal potential together, therefore the potential on an equipotential surface is constant everywhere. As these points all have equal potential, the gravitational potential difference is zero when moving along the surface, so no work is done when moving along an equipotential surface. The red lines on the diagram to the right represent equipotential surfaces.
Equipotential surfaces are surfaces which are created through joining points of equal potential together, therefore the potential on an equipotential surface is constant everywhere. As these points all have equal potential, the gravitational potential difference is zero when moving along the surface, so no work is done when moving along an equipotential surface. The red lines on the diagram to the right represent equipotential surfaces.
gravitational potential (V) is inversely proportional to the distance between the centres of the two objects (r). This can be represented on a graph of potential (V) against distance r.
Gravitational field strength (g) at a certain distance can be measured by drawing a tangent to the curve at that distance and calculating its gradient, then multiplying by -1:
If you plot a graph of gravitational field strength (g) against distance (r), you can find the gravitational potential difference by finding the area under the curve.
Coulombs law
Coulomb's law states that the magnitude of the force between two point charges in a vacuum is directly proportional to the product of their charges, and inversely proportional to the square of the distance between the charges.
Where & is the permittivity of free space, Q,/Q, are charges, r is the distance between charges.
Air can be treated as a vacuum when using the above formula, and for a charged sphere, charge may be assumed to act at the centre of the sphere.
If charges have the same sign the force will be repulsive, and if the charges have different signs the force will be attractive.
The magnitude of electrostatic forces between subatomic particles is magnitudes greater than the magnitude of gravitational forces, this is because the masses of subatomic particles are incredibly small whereas their charges are much larger.