Energy

Содержание и основные понятия

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Alterna · physics · 4.4
Energy
Potential and kinetic energy, transformation
Energy is the ability to do work. The ball on the roof has potential energy. Falling, it turns into kinetic, but the sum is always constant.
GEF · Grade 7
PIF · Baseline
01
Mechanical energy
Energy is the body's ability to do work.
Energy
Energy
is the physical value of the body's ability to perform work.
Joul (J)
.
Potential energy
Potential energy
- energy caused by the interaction of bodies or body parts.
E
p
= m · g · h
- for a body raised to height h.
E
p
= k · Δl² / 2
- for a deformed spring.
kinetic energy
kinetic energy
- the energy of the moving body.
E
k
= m · v² / 2
where m is the mass of the body, v is the speed.
Work and energy linkages
Work is equal to energy change: A = ΔE. If the force does positive work, the body energy increases.
02
Energy conversion
Potential to kinetic, back and forth.
Law on Energy Conservation
In a closed system
Total mechanical energy retained
:
E
p
+ E
k
= const
Example: The ball falls from a height. Only E at the top
p
Downstairs - only E
k
In the middle is the sum.
If there is friction, part of the mechanical energy becomes internal (heat), but the full energy is stored.
📘
The Cartoon — Energy Change
IV-039 · E_p + E_k = const
Mass m:
1
kg
Length L:
2
m
Tearing:
Press Start
🎢
American Rockets — Energy Transforming
IV-039B · Ep ~ Ek — The ball rolls along the path, energy is diverted
Start height:
15
m
Mass:
1
kg
Tearing:
The Law of Energy Conservation — The Basic Law of Nature
Energy doesn't come out of nowhere and disappears without a trace. It just turns from one species to another and passes from one body to another.
Law on Energy Conservation
one of the fundamental laws of physics.
C
What needs to be understood
Outcome 1
Explain the physical meaning of the topic "Energy" through the model, not just the formula.
Outcome 2
To distinguish and correctly use terms: kinetic energy, potential energy, mechanical energy.
Outcome 3
Indicate the conditions for the applicability of the law, verify units and limit cases.
T
Terms of the topic
The definition should indicate the physical meaning, not a substitute for a domestic synonym.
kinetic energy
The power of mechanical motion is mv2/2 in classical mechanics.
Potential energy
Interface energy dependent on the mutual position of the bodies or parts of the system.
mechanical energy
The sum of the kinetic and potential energies of the chosen mechanical system.
Law on Energy Conservation
The power of the closed system does not arise or disappear, but only passes between the forms and parts of the system.
F
Origin and conclusion of the formulas
The fundamental law cannot be "proven" by algebras: for each record, it is stated whether it is a definition, an experimental law, or a model effect.
E
к
=
m
v
2
2
E_{\text{к}}=\frac{mv^2}{2}
E
to
​
=
2
m
v
2
​
model effect
kinetic energy.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
A
=
F
s
=
m
a
s
A=Fs=mas
A
=
F
s
=
ma
s
A constant equivocal force in the breakout works on the body.
v
2
=
2
a
s
v^2=2as
v
2
=
2
a
s
The kinematic connection for the equidistant movement from rest gives the work of acceleration to the path.
A
=
m
a
s
=
m
v
2
2
A=mas=\frac{mv^2}{2}
A
=
ma
s
=
2
m
v
2
​
The work needed to disperse determines the body's acquired kinetic energy.
Conditions:
Classic mechanics; the material point or body making a purely progressive motion, v being the speed of the centre of the masses. If there is rotation or internal motion, the full kinetic energy shall additionally contain the corresponding summation; the speed is much less than the speed for light.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
E
п
=
m
g
h
E_{\text{п}}=mgh
E
c/
​
=
m
g
h
model effect
Potential energy.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
F
тяж
=
m
g
F_{\text{тяж}}=mg
F
claim
​
=
m
g
In a homogeneous field near the Earth's surface, gravity is constant in the module.
A
внеш
=
F
h
=
m
g
h
A_{\text{внеш}}=Fh=mgh
A
Outside
​
=
F
h
=
m
g
h
When rising slowly, the external force balances the load and does work at height h.
E
п
−
E
п
,
0
=
m
g
h
E_{\text{п}}-E_{\text{п},0}=mgh
E
c/
​
−
E
c/
,
0
​
=
m
g
h
This work increases the energy of interaction with Earth; at zero at the reference level, Ep = mgh.
Conditions:
Small heights in a homogeneous field of gravity, g constant; h is calculated from the selected zero level of potential energy.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
!
Model boundaries and typical errors
Error: Forget model condition
You can't move the formula to any situation just because the letters match. The key condition of this topic is that energy is the ability to do work. The ball on the roof has potential energy. Falling, it turns into kinetic, but the sum is always constant.
How to Check the Mind
The formula is only applicable after selecting the system and assumptions. Then check the unit, vector direction and result behaviour at zero or very large parameter.
Σ
Conclusion on the topic
Energy
Energy is the ability to do work. The ball on the roof has potential energy. Falling, it turns into kinetic, but the sum is always constant.
Energy is the ability to do work. The ball on the roof has potential energy. Falling, it turns into kinetic, but the sum is always constant.
The formula is applicable only after the selection of the system and assumptions.
Any numerical result shall be accompanied by a unit, a sign and an explanation of its physical meaning.
The content is consistent with the FRP on Physics of the OS/OSS 2025 and the subject matter of the current lines of the PNP: I. M. Peryškin and co-authors (7–9), G. J. Mäkishev and coauthors (10–11), and with the lines "Engineers of the Future" and V. A. Kasyanov. The original texts are not reproduced, the text of the textbooks is not reproduced.