I 2.1.2 Discuss: Defining Distance and Displacement

1. You often hear people, particularly TV announcers, talk about a "high rate of

speed." What do you think they mean? According to the specifics of physics

definitions, what are they really saying?

2. What other "science" words do you hear getting thrown around in general

conversation? Do you think these words are being used in the precise way that

scientists use them?

3. What kinds of difficulties do you foresee when scientists and non-scientists try

to communicate?

BIUS TI

SE

Consider an ordinary, helium-filled party balloon with a volume of 2.2 ft3. the lifting force on the balloon due to the outside air is the net resultant of the pressure distribution exerted on the exterior surface of the balloon. using this fact, we can derive archimedes’ principle, namely that the upward force on the balloon is equal to the weight of the air displaced by the balloon. assuming that the balloon is at sea level, where the air density is 0.002377 slug/ft3, calculate the maximum weight that can be lifted by the balloon. note: the molecular weight of air is 28.8 and that of helium is 4.

The material that keeps its new shape after it is stretched is called?

Consider a 1000 w iron whose base plate is made of 0.5 cm thick aluminum alloy 2024-t6 (ρ = 2770 kg/m3 and cp = 875 j/kg°c). the base plate has a surface area of 0.03 m2. initially, the iron is in thermal equilibrium with the ambient air at 22°c. assuming 90% of the heat generated in the resistance wires is transferred to the plate, determine the minimum time needed for the plate temperature to reach 200°c.