Fundamental vs Derived Quantities
Kev sim yog qhov tseem ceeb ntawm physics thiab lwm yam kev tshawb fawb lub cev. Cov kev xav thiab lwm yam kev xav tau raug txheeb xyuas thiab tsim los ua qhov tseeb ntawm kev tshawb fawb los ntawm kev sim ua. Kev ntsuas yog ib feem tseem ceeb ntawm kev sim, qhov loj ntawm thiab kev sib raug zoo ntawm ntau lub cev sib txawv yog siv los txheeb xyuas qhov tseeb ntawm txoj kev xav lossis kev xav tau sim.
Muaj ntau qhov ntau ntawm lub cev uas feem ntau ntsuas hauv physics. Cov khoom no raug suav tias yog qhov tseem ceeb ntawm cov khoom siv los ntawm kev sib tham. Siv cov kev ntsuas rau cov khoom no thiab cov kev sib raug zoo ntawm lawv, lwm qhov ntau ntawm lub cev tuaj yeem muab tau. Cov khoom no yog hu ua derived quantities.
Qhov Tseem Ceeb
Ib pawg ntawm cov chav hauv paus tau txhais hauv txhua qhov system, thiab cov khoom siv lub cev raug hu ua qhov tseem ceeb. Cov chav hauv paus yog txhais los ntawm nws tus kheej, thiab feem ntau qhov ntau yog ntsuas ncaj qha hauv lub cev.
Feem ntau, ib qho system ntawm chav tsev yuav tsum muaj peb lub tshuab (ntau, ntev, thiab sijhawm). Ib chav hluav taws xob kuj yuav tsum tau. Txawm hais tias cov chav nyob saum toj no tuaj yeem txaus, rau qhov yooj yim ob peb lwm cov chav nyob hauv lub cev tau suav tias yog qhov tseem ceeb. c.g.s (centimeter-gram-thib ob), m.k.s (meter-kilogram thib ob), thiab f.p.s (ko taw-phaus-thib ob) yog yav tas los siv cov tshuab nrog cov ntsiab lus.
SI unit system tau hloov ntau lub tshuab qub. Nyob rau hauv SI system ntawm units, los ntawm txhais tau tias, raws li xya lub cev muaj nuj nqis yog xam raws li qhov tseem ceeb lub cev muaj nuj nqis thiab lawv units raws li lub cev lub cev units.
| Quantity | Unit | Symbol | Dimensions |
| Length | Meter | m | L |
| mass | kg | kg | M |
| sijhawm | Seconds | s | T |
| Electric Current | Ampère | A | |
| Thermodynamic Temp. | Kelvin | K | |
| Ntau Yam | Moob | mol | |
| luminous siv | Candela | cd |
Drived Quantities
Drived kom muaj nuj nqis yog tsim los ntawm cov khoom ntawm lub hwj chim ntawm lub hauv paus units. Hauv lwm lo lus, cov khoom no tuaj yeem muab tau los ntawm cov khoom siv tseem ceeb. Cov koog no tsis tau txhais ntawm nws tus kheej; lawv nyob ntawm lub ntsiab txhais ntawm lwm units. Cov khoom uas txuas nrog rau qhov muab tau los yog hu ua derived quantities.
Piv txwv li, xav txog vector kom muaj nuj nqis ceev. Los ntawm kev ntsuas qhov kev ncua deb ntawm ib yam khoom thiab lub sijhawm coj mus, qhov nruab nrab ceev ntawm cov khoom tuaj yeem txiav txim siab. Yog li ntawd, ceev yog ib tug derived kom muaj nuj nqis. Cov nqi hluav taws xob kuj yog qhov muab tau los ntawm qhov uas nws tau muab los ntawm cov khoom siv tam sim no thiab lub sijhawm coj mus. Txhua qhov derived ntau muaj derived units. Cov khoom tuaj yeem tsim tau.
| Lub cev kom muaj nuj nqis | Unit | Symbol | ||
| dav hlau kaum | Radian (a) | rad | – | m·m-1 =1 (b) |
| lub kaum ntse ntse | Steradian (a) | sr (c) | – | m2·m-2 =1 (b) |
| frequency | Hertz | Hz | – | s-1 |
| force | NYIAJ Newton | N | – | m·kg·s-2 |
| siab, ntxhov siab | Pascal | pa | N/m2 | m-1·kg·s-2 |
|
zog, ua haujlwm, kom muaj cua sov |
Joule | J | Nm | m2·kg·s-2 |
| Watt | W | J/s | m2·kg·s-3 | |
| nqi hluav taws xob, kom muaj nuj nqis | C | – | A·s | |
| hluav taws xob muaj peev xwm sib txawv, electromotive force | Volt | V | W/A | m2·kg·s-3·A-1 |
| Farad | F | C/V | m-2·kg-1·s4·A 2 | |
| hluav taws xob tiv thaiv | Ohm | V/A | m2·kg·s-3·A-2 | |
| hluav taws xob conductance | NWS Siemens | S | A/V | m-2·kg-1·s3·A 2 |
| magnetic flux | Weber | Wb | V·s | m2·kg·s-2·A-1 |
| magnetic flux density | Tesla | T | Wb/m2 | kg·s-2·A-1 |
| inductance | Henry | H | Wb/A | m2·kg·s-2·A-2 |
| Celsius kub | °C | – | K | |
| luminous flux | Lumen | lm | cd·sr (c) | m2·m-2·cd=cd |
|
illuminance |
Lux | lx | lm/m2 | m2·m-4·cd=m-2·cd |
| kev ua haujlwm (ntawm radionuclide) | Becquerel | Bq | – | s-1 |
| absorbed koob tshuaj, specific zog (imparted), kerma | Grey | Gy | J/kg | m2·s-2 |
| dose equivalent (d) | Sievert | Sv | J/kg | m2·s-2 |
| kev ua haujlwm catalytic | Katal | kat | s-1·mol | |
Dab tsi yog qhov txawv ntawm Qhov Tseem Ceeb thiab Qhov Tau Txais?
• Cov khoom tseem ceeb yog qhov ntau npaum li cas ntawm ib chav tsev, thiab lawv tau txiav txim siab ntawm lwm qhov ntau.
• Cov khoom tau los yog raws li qhov tseem ceeb, thiab lawv tuaj yeem muab tau raws li qhov tseem ceeb.
• Hauv SI units, derived units feem ntau muab cov npe ntawm cov neeg xws li Newton thiab Joule.
