סוגיות בסביבה, קיימות ושמירת טבע - אב"ג
- 186 שאלות
- 929 תגובות
- 0% הושלמו
- equalizer סטטיסטיקות
- share שתף
Discuss, Learn and be Happy דיון בשאלות
help
brightness_4
brightness_7
format_textdirection_r_to_l
format_textdirection_l_to_r
CO:
1
| done | ||
מיין לפי
מוניטין: 20
brain
מוניטין: 924
CObra-in
מוניטין: 2095
מעניין שחושבים על האדם ולא על הסביבה לשם שינוי
מוניטין: 786
CO דומה לCEO, בשביל להיות CEO צריך מוח
מוניטין: 0
CO – the silent lobbyist for haemoglobin vacancies
Carbon monoxide isn’t interested in warming the planet—that job belongs to its more photogenic sibling, CO₂. CO’s real talent is outcompeting O₂ for your haemoglobin’s binding sites (≈ 250 × affinity). The result: hypoxic tissues, impaired judgement, and—if exposure persists—an involuntary nap from which one does not awaken. Calling it a climate threat is like criticising a pickpocket for failing to pay income tax: technically true, but hilariously beside the point. 🖤
Particle motion is affected by:
1
| done |
מיין לפי
The drag force:
1
| done | ||
מיין לפי
מוניטין: 0
GPT explains (level =C2; CEFR aligned):
Determinants of drag force on a particle moving through a fluid
In classical fluid mechanics the retarding or drag force arises from the viscous stresses transmitted by the surrounding fluid layer and, under laminar Stokes conditions, scales linearly with the dynamic viscosity μ of the fluid (𝐹ᴅ = 6πμrv for a sphere of radius r and velocity v). The intrinsic viscosity or “stickiness” of the particle itself is largely irrelevant; what matters is how readily adjacent fluid layers can shear past one another and regenerate the boundary layer. Density enters only indirectly via the Reynolds number that signals the transition to turbulence. Consequently, colour, superficial texture and other non-hydrodynamic properties do not feature in the governing equations: drag is controlled by the viscosity of the carrier fluid, not by the particle’s internal rheology.
The characteristic time τ:
1
| done | ||
מיין לפי
מוניטין: 0
יש טעות, לםי ההרצאה ונוסחת טאו. התשובה הנכונה הינה B. הסבר:The correct answer is B: τ is the reaction time for a particle to adjust when the flow velocity changes.
⸻
Why τ ≠ “just particle size” (and why B is the real star)
1. Definition of τ
In fluid mechanics, the characteristic time (also called the relaxation time) is how long it takes for a particle’s velocity to “catch up” to a suddenly altered fluid velocity. Mathematically:
τ = \frac{m_p}{6\pi\,μ\,R}
= \frac{ρ_p \, R^2}{9\,μ}
where
• m_p = particle mass (∝ ρ_p\,R^3),
• R = particle radius,
• μ = fluid viscosity,
• ρ_p = particle density.
2. Dependence on multiple factors
• Particle size (R) appears, but squared—not the whole story (so A is over-simplified).
• Fluid viscosity (μ) sits proudly in the denominator—more viscous fluid = slower response (so D is outright false).
• Particle density (ρ_p) also ramps τ up or down, so heavy particles take longer to adapt (directly contradicting C).
3. Physical interpretation
• Imagine plowing a bowling ball vs. a ping-pong ball through honey. The bowling ball (large, dense) resists changes in your push and lags far behind. Its τ is huge.
• The ping-pong ball (tiny, light) flits along almost instantly—its τ is minuscule.
• τ thus quantifies the “inertia vs. drag” battle and tells you exactly how long particles need to resign themselves to the new flow regime.
According to the exercise solved in the video presentation, at t=τ:
1
| done |
מיין לפי
מוניטין: 354
דעיכה אקספוננציאלית ומה קורה ב־
τ
τ:
τ
τ (טאו) = קבוע זמן.
מראה תוך כמה זמן הגודל "נחלש" בצורה משמעותית.
בתהליך של דעיכה אקספוננציאלית (כמו ירידת מהירות עם הזמן):
אחרי זמן
τ
τ → הגודל יורד ל־37% מהערך ההתחלתי.
📌 זכרי: "טאו = שליש פלוס טיפה" → 0.37
אחרי חצי מזמן
τ
τ → נשארים עם 61% מהערך.
Increasing the emitted particle size:
1
| done | ||
מיין לפי
Nanoscale particles:
1
| sentiment_very_satisfied | ||
Grouping of smoke particles:
1
| done |
מיין לפי
מוניטין: 0
Smoke-particle networking events (“aggregation”)🚬
When fine aerosols bump into one another they sometimes socialise:
1. Coagulation – single ultrafines merge into larger, fewer entities.
2. Numerical drop – particle count per cubic centimetre goes down; mass may stay put, but size distribution shifts right.
3. Filtration bonus – bigger agglomerates are easier for cyclones, bag filters and even nasal hairs to intercept.
Hence the only intellectually defensible choice is all of the above. Anything else is either half-true or half-baked—take your pick. 😶🌫️
The effects of air pollution can be reduced if:
1
| done | ||
מיין לפי
We can group and make particles larger, if:
1
| sentiment_very_satisfied |
מיין לפי
מוניטין: 0
“We can group and make particles larger, if: All of the above.”
Ah, the art of turning a stealthy nanoparticle army into chunky casualties—because nothing says “problem solved” like forcing those little devils to clump up and drop out. 😏
1. Taking advantage of the characteristic time τ
• By pulsing the gas flow (think rapid on–off cycles), you exploit each particle’s inertia. They can’t keep up with sudden velocity shifts (τ), so they collide and agglomerate into heftier clumps.
2. Inducing velocity variation in the exhaust system
• Helmholtz resonators, fluidic diodes, or even simple baffles introduce local eddies and shear. Tiny particles slam into one another where flow speed diverges, fostering coalescence.
3. Designing the exhaust system via a mathematical model
• CFD and inertial‐collision kinetics let engineers predict where clusters will form best—so you don’t just spray and pray, you engineer agglomeration hotspots.
4. Result: Larger “grenades” of particulate
• Once particles grow beyond a critical diameter, gravity and inertial impaction reclaim them. They rain down into scrubbers, filters, or the bottom of your hood—no more aerial ninja assaults on your lungs. 🤡
Bottom line: It’s not witchcraft—it’s fluid‐mechanics theatre. Tune your pulses, tune your geometry, run the numbers