The "after glow" from some clock faces is caused by atoms
1) being excited,
2) vibrating at frequencies greater than a million billion times per second,
3) remaining for some time in a state of excitation before de-exciting,
and materials exhibiting this property are called
4) fluorescent.
5) phosphorescent.
6) incandescent.
7) luminescent.
Answer: 3, 5
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Addition by 1. Components: Find the magnitude and direction of the resultant of the three force vectors, 
,
, and 
, shown in the figure. These vectors have the following magnitudes: A = 5.0 lb, B = 7.9 lb, and C = 8.0 lb. Express the direction of the resultant by specifying the angle it makes with the +x-axis, with counterclockwise angles taken to be positive.
style="vertical-align: 0.0px;" height="307" width="314" /> Fill in the blank(s) with the appropriate word(s).
Doppler radar can
a. catch speeders b. measure the speed of a pitcher's fastball c. detect tornadoes d. do all of the above
Raul is attending a workshop, but he is having difficulty hearing the speaker because the people behind him are talking. What type of barrier to effective listening is Raul experiencing?
a. Psychological barrier b. Nonverbal distraction c. Grandstanding d. Physical barrier
What is happening when two plates are smashing into one another?
A. Precession causes mountains to be built up; earthquakes and volcanoes may also occur. B. Subduction causes mountains to be built up; earthquakes and volcanoes may also occur. C. Rifting causes mountains to be built up; earthquakes and volcanoes may also occur. D. nothing