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Questions and Answers
What is the approximate fraction of second-hand air in a room when measuring CO2 levels?
What is the approximate fraction of second-hand air in a room when measuring CO2 levels?
- $ rac{400}{40,000}$ (correct)
- $ rac{300}{40,000}$
- $ rac{500}{40,000}$
- $ rac{200}{40,000}$
What is the approximate speed of mucus particles falling under gravity?
What is the approximate speed of mucus particles falling under gravity?
- $3 ext{ cm s}^{-1}$ for droplets of radius 10 µm
- $1 ext{ cm s}^{-1}$ for droplets of radius 10 µm
- $2 ext{ cm s}^{-1}$ for droplets of radius 10 µm (correct)
- $2 ext{ cm s}^{-1}$ for droplets of radius 5 µm
How is the mortality rate for a particular cancer defined?
How is the mortality rate for a particular cancer defined?
- The likelihood of developing cancer in that year
- The probability that a person of age t dies from that cancer at that age (correct)
- The cumulative risk of dying from that cancer over a lifetime
- The expectation of dying from any cause at age t
What does the variable 'K' represent in the model for cancer mortality?
What does the variable 'K' represent in the model for cancer mortality?
Which factor influences the keeping of aerosol droplets suspended in the air?
Which factor influences the keeping of aerosol droplets suspended in the air?
What does a high Péclet number indicate about flow and diffusion?
What does a high Péclet number indicate about flow and diffusion?
In the context of a nanomotor, which of the following is the correct formula for work done?
In the context of a nanomotor, which of the following is the correct formula for work done?
What is the approximate information storage capacity of the human genome?
What is the approximate information storage capacity of the human genome?
What is required for a biochemical switch to operate effectively?
What is required for a biochemical switch to operate effectively?
Which of the following forces is typical for a nanomotor during its operation?
Which of the following forces is typical for a nanomotor during its operation?
In terms of cell signaling, what does 'cooperative binding' refer to?
In terms of cell signaling, what does 'cooperative binding' refer to?
What type of diseases are transmitted via aerosols?
What type of diseases are transmitted via aerosols?
What happens when the Péclet number is much less than 1?
What happens when the Péclet number is much less than 1?
What is the relationship between the mass of an animal and its ability to walk on land?
What is the relationship between the mass of an animal and its ability to walk on land?
Why can water striders walk on water while humans cannot?
Why can water striders walk on water while humans cannot?
In which scenario do gravity forces dominate over surface tension for droplets?
In which scenario do gravity forces dominate over surface tension for droplets?
How does the time to diffuse a distance scale with that distance according to the diffusion equation?
How does the time to diffuse a distance scale with that distance according to the diffusion equation?
What characterizes the time taken to move via flow across a distance?
What characterizes the time taken to move via flow across a distance?
Which of the following correctly describes the change in droplet shape as its size increases?
Which of the following correctly describes the change in droplet shape as its size increases?
What does the inequality regarding surface tension and gravity indicate for water striders?
What does the inequality regarding surface tension and gravity indicate for water striders?
Which factor limits the size of animals that can walk on land?
Which factor limits the size of animals that can walk on land?
Flashcards
Stress
Stress
The maximum force that an object can withstand before breaking or deforming.
Stress
Stress
The ratio of the force applied to the cross-sectional area of the object.
Surface Tension
Surface Tension
A measure of a fluid's resistance to deformation.
Bond Number
Bond Number
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Diffusion
Diffusion
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Diffusion Time
Diffusion Time
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Flow
Flow
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Flow Time
Flow Time
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Second-hand air fraction (f2nd)
Second-hand air fraction (f2nd)
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CO2 concentration in air and breath
CO2 concentration in air and breath
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Aerosol particle settling speed (u)
Aerosol particle settling speed (u)
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Cancer mortality rate (hC(t))
Cancer mortality rate (hC(t))
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Number of mutations for lethal cancer (K)
Number of mutations for lethal cancer (K)
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Péclet Number (Pe)
Péclet Number (Pe)
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Bond Number (Bo)
Bond Number (Bo)
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Nanomotor Force
Nanomotor Force
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Biological Switch
Biological Switch
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Cell Division
Cell Division
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Cell Signaling
Cell Signaling
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Study Notes
Biological Physics Revision Lecture Summary
-
Lecture 1: Fermi Estimation and King Kong
- Stress on femur is limited by bone strength (≤10⁹ Pa)
- Animal leg size is constrained by this.
- Mass scales with size cubed (h³), while load-bearing area of femurs scales with size squared (h²).
-
Lecture 2: Walking on Water
- Surface tension force must exceed gravity force.
- Surface tension scales with size linearly (h¹), while gravity scales with size cubed (h³).
- This explains why some creatures can walk on water but humans cannot.
-
Lecture 3: Dimensionless Numbers
- Dimensionless numbers (like the Bond number) compare competing forces.
- The Bond (Bo) number compares gravitational and surface tension forces.
- Little droplets are spherical because surface tension dominates.
- Larger droplets are flattened due to gravity.
-
Lecture 4: Diffusion, Flow, and Heart Attacks
- Diffusion time is proportional to the square of the distance.
- Diffusion is fast for short distances, slow for long distances.
- Flow is much faster than diffusion over large distances.
-
Lecture 5: Tiny Motors in Muscles
- Motors are very small, even at nanometer level.
- Maximum force in nanomotors is ~10⁻¹¹N.
- Energy is released from reactions to overcome distance.
-
Lecture 6: DNA Information and Gene Switches
- DNA storage capacity is enormous.
- Human genome store lots of information.
- Cellular signals trigger switches regulating proteins or genes.
-
Lecture 7: Airborne Infectious Diseases
- COVID-19 and other diseases spread via aerosols.
- Second-hand air has a higher concentration of relevant gases than the room air itself (e.g., CO₂).
-
Lecture 8: A Simple Model for Cancer Mortality
- Cancer mortality rate is related to age.
- A power law describes the age and cancer rate (cancer mortality increases with age).
- Cancer is a multi-step process (e.g., mutations).
-
Lecture 9: Evolution of Milk Drinking
- Evolution is related through common ancestry.
- The proportion of an allele in a population grows exponentially through the generations.
-
Lecture 10: Aerosol Particles
- Stokes drag affects how fast objects fall.
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