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| # | Thing | Description | Topic | Up/Down/Net | Score ▼ | |
|---|---|---|---|---|---|---|
| 701 | Observation | Active acquisition of information from a primary source | Physical sciences | +0 / -0 / 0 | 0.500000 | |
| 702 |  | Observatory | Location used for observing terrestrial or celestial events | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 703 |  | Ocean | Body of salt water covering most of Earth | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 704 |  | Ocean current | Directional mass flow of oceanic water | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 705 |  | Oceanic trench | Long and narrow depressions of the sea floor | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 706 |  | Oceanography | Scientific study of the ocean | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 707 |  | Ohm | SI derived unit of electrical resistance | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 708 |  | Oil drop experiment | Experiment to measure elementary electric charge | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 709 |  | Oil shale | Organic-rich fine-grained sedimentary rock containing kerogen | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 710 |  | Omega Centauri | Globular cluster in the constellation Centaurus | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 711 |  | Oort cloud | Distant planetesimals in the Solar System | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 712 | Optics | Branch of physics that studies light | Physical sciences | +0 / -0 / 0 | 0.500000 | |
| 713 |  | Orange (colour) | Colour located between red and yellow | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 714 |  | Orbit | Curved path of an object around a point | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 715 |  | Orbital mechanics | Field of classical mechanics concerned with the motion of spacecraft | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 716 |  | Ore | Rock or sediment with valuable metals, minerals and elements | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 717 |  | Organic chemistry | Subdiscipline of chemistry, focusing on carbon compounds | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 718 |  | Organic compound | Carbon-containing chemical compound | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 719 |  | Organometallic chemistry | Study of organic compounds containing metal(s) | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 720 | Organophosphorus chemistry | Organic compound with at least one covalent carbon–phosphorus bond | Physical sciences | +0 / -0 / 0 | 0.500000 | |
| 721 |  | Organosilicon chemistry | Organometallic compound containing carbon–silicon bonds | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 722 |  | Orion (constellation) | Constellation straddling the celestial equator | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 723 |  | Orion Nebula | Diffuse nebula in the constellation Orion | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 724 |  | Oscillation | Repetitive variation of some measure about a central value | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 725 |  | Osmosis | Movement of molecules to lower concentration | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 726 |  | Ounce | Unit of mass | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 727 |  | Outer space | Void between celestial bodies | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 728 |  | Oxide | Chemical compound with an oxygen atom | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 729 |  | Oxygen | Chemical element with atomic number 8 (O) | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 730 |  | Ozone | Triatomic oxygen molecule | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 731 |  | PH | Measure of the level of acidity or basicity of an aqueous solution | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 732 |  | Paleogene | First period of the Cenozoic Era | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 733 | Paleozoic | First era of the Phanerozoic Eon | Physical sciences | +0 / -0 / 0 | 0.500000 | |
| 734 |  | Palladium | Chemical element with atomic number 46 (Pd) | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 735 |  | Pangaea | Supercontinent from the late Paleozoic to early Mesozoic eras | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 736 |  | Parallax | Difference in apparent position with viewing angle | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 737 |  | Parsec | Unit of length in astronomy | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 738 |  | Particle accelerator | Research apparatus for particle physics | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 739 | Particle detector | Device used to detect, track, and/or identify ionising particles | Physical sciences | +0 / -0 / 0 | 0.500000 | |
| 740 |  | Particle physics | Study of subatomic particles and forces | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 741 |  | Pascal (unit) | SI derived unit of pressure | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 742 |  | Pearl | Hard object produced within a living shelled mollusc | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 743 |  | Peat | Accumulation of partially decayed vegetation | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 744 |  | Pedosphere | Outermost layer of the Earth | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 745 |  | Periodic table | Tabular arrangement of the chemical elements | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 746 |  | Permafrost | Type of soil in frozen state | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 747 |  | Permian | Sixth and last period of the Paleozoic Era | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 748 |  | Permian–Triassic extinction event | Earth's most severe extinction event | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 749 |  | Petrology | Study of rocks in geology | Physical sciences | +0 / -0 / 0 | 0.500000 |
| 750 |  | Phanerozoic | Fourth and current eon of the geological timescale | Physical sciences | +0 / -0 / 0 | 0.500000 |
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