The strength of friction

Содержание и основные понятия

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Alterna · physics · 2.4
The strength of friction
Sliding, rest, friction in nature and technology
Truth is an invisible enemy and an invisible friend. Without it, we could not walk, but it slows down cars and wears out the details. How can we control that power?
GEF · Grade 7
PIF · Baseline
01
The strength of friction
Why is the moving body stopping?
The strength of friction
The strength of friction
is the force generated by contact with the surface of the bodies and directed along the surfaces
opposite
moving.
Reason: Microscopic surface irregularities cling together.
F
t/
= μ · N
where μ is the coefficient of friction, N is the force of the support leg reaction (for horizontal surface N = mg).
Types of friction
The Worming of Peace
— A force preventing the beginning of movement
Slide friction
— when one body moves on the surface of the other
Rolling friction
— rolling (wheel on the road) usually less friction than slipping
⛷
Friction Force — Surface
IV-019 · surface selection + inclination angle
Surface:
Angle:
20
°
Mass m:
5
kg
02
The Worming of Peace
Why doesn't the table move when we're pushing softly?
The Worming of Peace
The Worming of Peace
is the force that arises when trying to move the body, but the body is still resting. It is equal to the force applied (until it does not exceed the maximum friction of rest).
The friction of the rest is the friction of slipping, which allows us to walk, and the machines to move.
Useful friction
Without the friction of the rest, we could not walk; the legs would slip; the tires of cars would stick to the road precisely because of the tremor of the peace; and the tyre sheariness increases friction.
03
Twilight in Nature and Technology
When friction is a friend and when is an enemy.
How to Reduce Friction
Lubricant (oil, greasy) — Fills with roughness
Ball bearings and roller bearings — Replace friction with rolling friction
Surface polishing
Air bag (artificial vessels)
How to Increase Friction
Sheriffed tyres, winter shoes
Brake pads — Friction Material
Reaper Paper — For Scraping
That's curious.
The bearings reduce friction by 20–30 times; the first ball bearing was patented in 1869; without the wheel bearings, the cars would be worn out in weeks.
C
What needs to be understood
Outcome 1
Explain the physical meaning of the topic "The power of friction" through the model, not just through the formula.
Outcome 2
Discern and correctly use terms: friction, friction of rest, frictions of slip.
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.
friction
Communicating bodies that prevent their relative movement or formation.
the friction of the rest
The friction force without slip, which adjusts to the limit value and prevents the start of traffic.
friction slipping
Force preventing relative slip of contact surfaces.
coefficient of friction
A disproportional dry friction model coefficient linking the friction force of slip to the normal reaction.
support leg reaction
The force of turgency with which the support acts on the body in contact with it.
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.
F
тр
=
μ
N
F_{\text{тр}}=\mu N
F
t/
​
=
μ
N
empirical law
The friction of slipping.
The following is an indication of the definition, experience or law from which this entry arises and where it is applicable.
F
тр
∼
N
F_{\text{тр}}\sim N
F
t/
​
∼
N
The dry surface experiments establish the approximate proportionality of the friction force of normal reaction slip.
μ
=
F
тр
N
\mu=\frac{F_{\text{тр}}}{N}
μ
=
N
F
t/
​
​
The dimensionless coefficient of friction μ shall be determined experimentally for the pair of surfaces.
F
тр
=
μ
N
F_{\text{тр}}=\mu N
F
t/
​
=
μ
N
The law records force modules; the friction force is directed against relative slipping.
Conditions:
Dry friction of solid surfaces in the normal range of loads and speeds; not applicable to tremors of rest as equality and viscous resistance.
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 change the formula to any situation just because it's a coincidence of letters. The key condition of this subject is that the friction of peace is the force that prevents the movement from starting.
How to Check the Mind
Slide friction — when one body moves on the surface of the other, then check the unit, vector direction and result behaviour at zero or very large parameter.
Σ
Conclusion on the topic
The strength of friction
Truth is an invisible enemy and an invisible friend. Without it, we could not walk, but it slows down cars and wears out the details. How can we control that power?
The Worm of Peace — A Force That Prevents the Start of Movement
Sliding friction — When one body moves on the surface of another
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.