Serial number	Key field	Frequency of occurrence
1	Teaching	581
2	Educational aids	385
3	Education	367
4	Educational assessment	310
5	Educator	161
6	Physicists	139
7	Newtonian mechanics	127
8	News and events	113
9	Careers and professions	106
10	Books	97
11	Lectures	96
12	Scholarly publishing	95
13	Measuring instruments	90
14	Chemical elements	86
15	Laboratories	82
16	Public policy and governance	73
17	Universities	72
18	Journal	69
19	Polymers	63
20	Batteries	58
21	Rotational dynamics	57
22	Funding	51
23	Energy conservation	50
24	Musical instruments	47
25	Learning and learning models	47
26	Friction	46
27	Electromagnetism	44
28	Students	44
29	History of science	42
30	Abstracts	41
31	Free-body diagrams	40
32	Visual system	39
33	Transition metals	38
34	Gravitational force	37
35	Outreach	37
36	Electrostatics	36
37	Lenses	34
38	Optical imaging	34
39	Scientific society and organization	34
40	Kinematics	32
41	General physics	30
42	Microphones	29
43	Interviews	29
44	Electrical circuits	27
45	Conference	26
46	General relativity	25
47	Special relativity	25
48	Leptons	25
49	Astronomers	24
50	Thermal instruments	24
51	Awards and Prizes	24
52	Text books	24
53	Magnetic equipment	24
54	Programming languages	24
55	Sensors	24
56	Corrections	24
57	Fundamental constants	23
58	Internet	23
59	Electrodynamics	23
60	Telecommunications engineering	23
61	Diversity in science	22
62	Buoyancy	22
63	Magnetic fields	22
64	Geometrical optics	22
65	Data acquisition	22
66	Regression analysis	21
67	National Aeronautics and Space Administration	21
68	Thermodynamic states and processes	21
69	Geodesy	20
70	Classical mechanics	20
71	Speed of sound	20
72	Oscilloscopes	20