On this graph, the black curve represents actual temperature measurements, the red curve represents models of the climate that include human emissions of greenhouse gases, and the blue curve represents models of the climate that include only natural factors but do not include human emissions of greenhouse gases. What is the key message that can be read from this graph?

A) Models support the conclusion that human emissions are driving global warming.
B) Different climate models give different predictions about how much global warming should be occurring.
C) Climate models can successfully reproduce Earth's climate for the first half of the 20th century, but after that, they are unable to account for actual temperature data.
D) Although some models support the idea that global warming is caused by human activity, other models do not and the cause therefore remains controversial.


A) Models support the conclusion that human emissions are driving global warming.

Physics & Space Science

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Calculate the average heat transfer coefficient for film-type condensation of water at pressures of 10 kPa and 101 kPa for (a) a vertical surface 1.5-m-high (b) the outside surface of a 1.5-cm-OD vertical tube 1.5-m-long (c) the outside surface of a 1.6-cm-OD horizontal tube 1.5-m-long and (d) a 10-tube vertical bank of 1.6-cm-OD horizontal tubes 1.5-m-long. In all cases, assume that the vapor velocity is negligible and that the surface temperatures are constant at 11°C below saturation temperature.

GIVEN
? Film condensation of water
FIND
The average heat transfer coefficient at pressure of 10 kPa and 101 kPa for
(a) A vertical surface of height (H) = 1.5 m
(b) The outside surface of a vertical tube Outside diameter (D) = 1.6 cm = 0.016 m
Height (H) = 1.5 m
(c) The outside surface of a horizontal tube Outside diameter (D) = 1.6 cm = 0.016m
Length (L) = 1.5 m
(d) A 10 tube vertical bank of horizontal tubes Outside diameter (D) = 1.6 cm
Length (L) = 1.5 m
ASSUMPTIONS
? Steady state
? Vapor velocity is negligible
? Surface temperatures (Ts) are constant at 11°C below saturation temperature
? Film thickness is much smaller than the pipe diameter
? Laminar condensate flow
SKETCH

PROPERTIES AND CONSTANTS
From Appendix 2, Table 13, the saturation temperatures for water at
101 kPa (Tsv1) = 100°C, therefore Ts = Tsv – 11°C = 89°C
10 kPa (Tsv2) = 45.3°C, therefore, Ts = 34.3°C
The film temperatures, as given in Section 9.4.1 are
Tfilm1 = Ts + 0.25 (Tsv – Ts) = 89°C + 0.25 (11°C) = 91.8°C
Tfilm2 = 34.3°C+ 0.25 (11°C) = 37.1°C
From Appendix 2, Table 13, for water at the film temperatures

Physics & Space Science

The source of a sonic boom may be a

A) whip. B) a high-speed bullet. C) both of these D) neither of these

Physics & Space Science

Why do we believe 90 percent of the mass of the Milky Way is in the form of dark matter?

A) The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo. B) Although dark matter emits no visible light, it can be seen with radio wavelengths, and such observations confirm that the halo is full of this material. C) Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk, suggesting that the halo is full of dark matter. D) Our view of distant galaxies is sometimes obscured by dark blotches in the sky, and we believe these blotches are dark matter located in the halo.

Physics & Space Science

During a lunar eclipse the Moon's phase must be

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Physics & Space Science