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### Course: High school physics—NGSS (DEPRECATED)>Unit 3

Lesson 3: Energy and fields

# Potential energy and position

The potential energy between two objects due to long-distance forces can be thought of as being stored in a field. When the objects move due to the field forces, the energy stored in the field decreases.  Created by Sal Khan.

## Want to join the conversation?

• how does the energy get into the field in the first place?
• Shouldn't the electric potential energy remain constant as we increase the distance since increasing the distance would decrease the magnitude of the force?
• no because it's talking about the POTENTIAL
• If the two charges that create a field get infinitely farther from each other, would that still increase the potential energy? Wouldn't the force become so weak that there would essentially be zero energy exerting on each other?
(1 vote)
• Why does Sal say "until these point charges "touch""?
(1 vote)
• Is there a time field?
(1 vote)

In physics, time is a fundamental concept, but it is not typically considered a field in the same way that other physical quantities are. Let me explain:

Definition of Time:

In classical, non-relativistic physics, time is defined by its measurement: it is what a clock reads. It is a scalar quantity, often denoted by the symbol (t), and is usually considered a fundamental quantity alongside length, mass, and charge.

Time can be combined mathematically with other physical quantities to derive concepts such as motion, kinetic energy, and time-dependent fields.

Unit of Measurement:

The unit of time in the International System of Units (SI) is the second (symbol: s). It has been defined since 1967 as “the duration of 9,192,631,770 cycles of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.”

This definition is based on the operation of a caesium atomic clock, which has become the practical standard for timekeeping worldwide.

Coordinate Time vs. Proper Time:

In relativistic physics (such as Einstein’s theory of relativity), there are two related concepts:

Proper time:
This is the physical time measured by a clock that is at rest relative to the observer. It corresponds to the time experienced by an observer moving along a specific trajectory.

Coordinate time:
This is the mathematical time defined in some coordinate systems. It is coordinate-dependent and is often considered non-physical.
Proper time is more fundamental, while coordinate time depends on the choice of coordinates and reference frames.

Fields in Physics:

In modern physics, everything is considered to be a “quantum field,” including spacetime itself. Fields describe how physical quantities (such as particles, forces, and energy) vary throughout space and time.
Spacetime is a four-dimensional continuum that combines three dimensions of space with one dimension of time. It is described by a field in relativistic theories like general relativity and quantum field theory.

In summary, while time is not typically treated as a field in classical physics, the concept of spacetime as a field plays a crucial role in modern physics. If you have any more questions or need further clarification, feel free to ask!

Hope this helps!

Happy Learning!

Angelina
(1 vote)
• How does energy cause so much stuff to happen in short amount of time?
(1 vote)
• It's the same amount of "stuff" happening. It's just transferred from one source to another. Batteries, for example, are just packs of potential chemical energy that transfers to electronics that makes it electrical energy or mechanical energy. The object is using the charge to work, since energy is the capacity something can work
(1 vote)