Which statement best describes the purpose of the vacuum inside a thermos? A. It prevents particles from transferring thermal energy between the inner and outer bottles.
B. It increases heat loss through conduction between the outer and inner bottles.
C. It prevents heat loss through radiation, which requires matter to transfer energy.
D. It allows for more collisions between the particles that make up the outer and inner bottles.

Total solidification times of three casting geometries are to be compared: a sphere, a cylinder, in which the length-to-diameter ration - 1.0, and a cube. volume = 1000 cm^3 for all three shhapes, and the same casting alloy is used. a) determine the solidification times of each geometry b) based on the results of part (a), which geometric element would make the best riser? c) if the mold constant = 3.5 min/cm^2 in chvorinov's rule, compute the total solidification time for each casting.

1. jay fills a wagon with sand (about 20 kg) and pulls it with a rope 30 m along the beach. he holds the rope 25° above the horizontal. the rope exerts a 20-n tension force on the wagon. how much work does the rope do on the wagon?

Which of the following is the main energy source for the sun? a. fission of hydrogen b. fusion of hydrogen c. fusion of helium d. fission of iron