A physical field can be thought of as the assignment of a physical quantity at each point of space and time. For example, in a weather forecast, the wind velocity during a day over a country is described by assigning a vector to each point in space. Each vector represents the direction of the movement of air at that point. As the day progresses, the directions in which the vectors point change as the directions of the wind change.
So a Field can be described by n-dimensional Mathematical function, for example: assignment of a scalar or vector to n-dimensional coordinates (time can also be a coordinate).
If there's influence from distance, we can say that between the cause of influence & affected body there's Field.
If affected bodies are influenced by Force, we can speak of Force Fields.
There are many Fields, including Gravitational Field of Earth, Electric Fields, Magnetic Fields.
Electric & Magnetic Fields are tied, forming Electromagnetic Fields that are changing with time.
Radio-TV Sattelites can receive or radiate Electromagnetic Fields into Space, for example.
Field Intensity.
Field Intensity is the vector sum of all forces exerted by a field on a unit mass, unit charge, unit magnetic pole, etc., at a given point within the field.
Units.
Almost every physical quantity has it's unit - either basic or derived.
| Quality | Quantity Symbol | Unit | Unit Symbol |
| length | l | meter | m |
| mass | m | kilogram | kg |
| time | t | second | s |
| electric current intensity | I | amper | A |
| temperature | T | kelwin | K |
| light source intensity, brightness | Iv | candela | cd |
Basic Physical Quantities.
| Quantity | Basic units | Particular unit name | Symbol |
| ampere-second | A · s | coulomb | C |
| per second | 1 / s | hertz | Hz |
| square meter | m · m | - | m2 |
| Force | kg · m/s2 | Newton | N |
| work | N · m | Joule | J |
Derived Units.
Acceleration & Force.
Applying force, we can accelerate movement of a body, change it's speed.
Change of speed (Δ v) divided by amount of time during which that change occured (Δ t), we can call 'acceleration' (a).
Force is a vector (quantity with direction). We can say: vector F, or write it as: F.
Speed & Velocity.
Speed & velocity are differing in that velocity is a vector (quantity with direction), whereas speed is quantity without direction.
Velocity (v) is length of the way (s) travelled in a given time (t).
Velocity is measured in meters per second (m/s).
Work.
Work (w) is force (F) times length of way (s).
Work is a vector.
When force (F) & way (s) are not on the same straight line, a component of force vector (Fs) that is along way is used in calculations of work (w).
Energy.
Energy is capability to do a work. Work causes change in energy quantity.
Energy cannot be created, but it can be transformed into another form (for example: chemical energy can be transformed to heat energy during burning process, solar or nuclear energy can be changed to electricity).
Potential energy is energy contained in certain system, for example in physical body mass in gravitational field of Earth.
Potential energy at initial position has value equal to work neccessary to move mass from initial position to new position.
w - potential energy.
Fc - gravitational force.
Δh - difference in position (height).
Potential energy can also be stored in other ways, for example: in a spring mechanism.
Kinetic energy is contained in physical body mass that is moving.
Kinetic energy depends only on the mass & velocity, but not on the starting position of the mass.
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