Discuss the observational differences between spiral, elliptical, and irregular galaxies
What will be an ideal response?
Elliptical galaxies (class E) have no disk, no spiral arms, and almost no gas and dust. They range from huge giants to small dwarfs. Spiral galaxies (class S) are disk-shaped and usually have spiral arms and contain gas and dust. Some of these have a central region shaped like an elongated bar and are called barred spiral galaxies (class SB). A few disk galaxies contain relatively little gas and dust; these are called lenticular galaxies (class S0). Irregular galaxies (class I) are generally shapeless and tend to be rich in gas and dust.
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Which of the following are (at least nearly) inertial reference frames and which are not? (Respond T if the frame is inertial, F if it is non inertial, and C if it is inertial for everyday purposes. The classification could be debatable, creating an opportunity to discuss the issues involved.)
(a) A non rotating frame floating in deep space (b) A frame floating in deep space that rotates at 1 rev/h (c) A non rotating frame attached to the sun (d) A frame attached to the surface of the earth (e) A frame attached to a car moving at a constant velocity (f) A frame attached to a roller-coaster car
A catapult is tested by Roman legionnaires. They tabulate the results in a papyrus and 2000 years later the archaeological team reads (distances translated into modern units):
angle of landing height = launch height. What is the initial velocity of launch of the boulders if air resistance is negligible? A) 44 m/s B) 1.4 m/s C) 22 m/s D) 0.69 m/s
A solar eclipse occurs when the
A) Sun passes into Earth's shadow. B) Moon passes into Earth's shadow. C) the Moon's shadow is cast on Earth. D) none of the above
A galvanometer calibrated to read current is
A) an ammeter. B) a voltmeter. C) an ohm meter. D) none of the above