Mechanical waves

Содержание и основные понятия

The wave spreads oscillation and energy between areas of the environment, and the particles of the medium fluctuate near balance and do not travel with the wave over long distances.
GEF · Grade 9
PIF · Baseline
Interactive model
wave
Wave length
Front
transversal wave
longitudinal wave
01
The physical picture
What happens and what boundaries the model has.
Main message
The wave spreads oscillation and energy between areas of the environment, and the particles of the medium fluctuate near balance and do not travel with the wave over long distances.
The transversal wave has a shift in the direction of distribution, and the longitudinal wave is along.
The frequency is set by the source, the speed by the properties of the environment.
The length of the wave is equal to the distance that the front passes in one period.
How to reason
First, name the system and the interaction, then select the values, and only then write down the law. The formula works within the model's assumptions.
02
Laws and values
Symbols should be read as a relationship of values, not as a recipe for substitution.
v
=
λ
ν
v=\lambda\nu
v
=
λ
ν
The connection between speed, length and frequency
λ
=
v
T
\lambda=vT
λ
=
v
T
Wave length
Review of the situation
At a frequency of 5 Hz and a speed of 20 m/s, the wave length is 4 m.
04
Links and application
In the real world
At a frequency of 5 Hz and a speed of 20 m/s, the wave length is 4 m.
Model verification
Compare the prediction with observation, evaluate the units, the order of magnitude and the influence of the factors not taken into account. Disparity does not always mean an error of law: often idealization is no longer sufficient.
C
What needs to be understood
Outcome 1
Explain the physical meaning of the topic "Mechanical Waves" through the model, not just the formula.
Outcome 2
Clear and correct use of terms: wave, wave length, front.
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.
wave
Distributive disturbance, energy and impulse without transport of the substance as a whole.
Wave length
The distance between the nearest points of the wave, which fluctuate in the same phase.
Front
The surface of the wave points, which fluctuate in the same phase.
transversal wave
A wave in which fluctuations are directed in the direction of proliferation.
longitudinal wave
A wave in which fluctuations occur along the direction of proliferation.
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.
v
=
λ
ν
v=\lambda\nu
v
=
λ
ν
model effect
The connection between speed, length and frequency.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
s
T
=
λ
s_T=\lambda
s
T
​
=
λ
In one period the disturbance spreads over one wave length.
v
=
s
T
T
=
λ
T
v=\frac{s_T}{T}=\frac{\lambda}{T}
v
=
T
s
T
​
​
=
T
λ
​
The speed of the wave is equal to the distance travelled by the front over the period divided by the period.
ν
=
1
T
⇒
v
=
λ
ν
\nu=\frac{1}{T}\Rightarrow v=\lambda\nu
ν
=
T
1
​
⇒
v
=
λ
ν
Replacement of the back period by frequency results in wave communication.
Conditions:
A periodic wave in a homogeneous environment with a certain phase speed; and , are related to the same wave.
Monitoring:
The dimensions of both parts shall coincide; the result shall be checked for sign, order and limit case.
λ
=
v
T
\lambda=vT
λ
=
v
T
model effect
The length of the wave.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
s
=
v
t
s=vt
s
=
v
t
In a homogeneous environment, the front of the wave spreads at a constant speed of v.
t
=
T
t=T
t
=
T
The time is considered for one complete change of source.
s
(
T
)
=
v
T
=
λ
s(T)=vT=\lambda
s
(
T
)
=
v
T
=
λ
The distance travelled by the wave over the period is, by definition, the length of the wave.
Conditions:
A periodic wave at a constant speed of v in a homogeneous environment; T is the source and wave period.
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 it's a coincidence of letters. The key condition of this topic is that the cross wave has a shift in the direction of proliferation, the longitudinal one along.
How to Check the Mind
The frequency is set by the source, the speed is the properties of the environment. Then check the units, the direction of the vectors, and the behaviour of the result at zero or very large parameter.
Σ
Conclusion on the topic
Mechanical waves
The wave spreads oscillation and energy between areas of the environment, and the particles of the medium fluctuate near balance and do not travel with the wave over long distances.
The transversal wave has a shift in the direction of distribution, and the longitudinal wave is along.
The frequency is set by the source, the speed by the properties of the environment.
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.