Process of Science: Most galaxies do not obey Hubble's Law perfectly. Why do we not take this as evidence that Hubble's law (and the theory of the expanding universe) is incorrect?
What will be an ideal response?
Hubble's law describes motions due only to expansion of the universe. In reality we expect (and observe) that actual galaxies experience gravitational effects from other objects and galaxies they encounter, making their motions slightly different from the pure Hubble's law prediction.
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If a force is applied parallel to a reinforcing phase of a composite material, the elastic modulus is calculated with the rule of _________.
Fill in the blank(s) with the appropriate word(s).
Which observation(s) and/or experiment(s) demonstrate ways that the chemical building blocks of life (amino acids and DNA bases) could have originated on the early Earth?
A) Amino acids and DNA bases form from simple chemical reactions in experiments simulating the early Earth atmosphere. B) These complex molecules have been found within meteorites. C) Experiments have shown that naturally occurring clays can catalyze the formation of RNA strands. D) All of the above
In cryogenic surgery, a small spherical probe is brought into contact with the diseased tissue which is frozen and thereby destroyed. One such probe can be modeled as a 3-mm diameter sphere whose surface is maintained at 240 K when the surrounding tissue is at 314 K. During the surgical procedure, a thin layer of tissue freezes around the probe at a temperature of 273 K. Assuming that the thermal conductivity of a frozen tissue is 1.5 W/(m K) and the heat transfer mechanism at the surface is described by the effective convective coefficient of 50 W/(m2 K), estimate the thickness of frozen tissue formed during a 30 min long operation.
GIVEN
Diameter of sphere(D1)= 3 mm, r1=0.0015 m
Probe surface temperature(Tp)= 240 K
Surrounding tissue temperature(Tt)= 314 K
Tissue freezing temperature(Tf)= 273 K
Thermal conductivity of frozen tissue(kt)= 1.5 W/(m K)
Effective convective coefficient (h?)=50 W/(m2 K)
Operation time (t)= 30 min
FIND
Thickness of a frozen tissue formed
ASSUMPTIONS
1 dimensional Steady state conditions persist
Negligible contact resistance between probe and frozen tissue.
Constant properties.
SKETCH
Albedo changes may result from ______________ pollution
a. smog b. particulate c. gas d. noise