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SI Units In this presentation you will: explore International System (SI) units Next >

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When measuring physical quantities in science, it is essential to use standard units. Next > They are important for communicating scientific information. Introduction NASA lost a $300 million Mars orbiter because one engineering team used metric units while another used United States customary units for a key spacecraft operation.

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Next > Introduction After a ten month journey, the space craft entered the atmosphere too low and burned up. US customary units, sometimes called the American system or “English units,” is based upon the Imperial system.

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Next > The International System (SI) Units The SI system (Le Système International d’Unités) has been accepted by the scientific community for measuring quantities. There are seven fundamental base units from which all others are derived. Quantity Symbol Unit Unit Symbol Length l meterm Massmkilogramkg Timetseconds Temperature T or kelvinK Amount of substancenmolemol Electric current I ampereA Luminous intensity IvIv candelacd

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Next > Length (l) Standard unit: meter Symbol: m The meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. 1 km = 1000 m 1 mm = m 1μm = m 1 nm = m

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Next > Mass (m) Standard unit: kilogram Symbol: kg The kilogram is equal to the mass of an object known as the international prototype of the kilogram. 1 tonne = 1000 kg 1 g = kg 1 mg = kg The kilogram is the only SI unit that is still defined by an object. However, work is underway to define it in terms of a physical constant.

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Next > Time (t) The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. 1 min = 60 s 1 hour = 3600 s 1 ms = s 1 μs = s 1 ns = s Standard unit: second Symbol: s

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Next > Temperature (T or q) The kelvin, unit of thermodynamic temperature, is the fraction 1/ of the thermodynamic temperature of the triple point of water. The kelvin is based on absolute zero, the lowest temperature possible. Standard unit: kelvin Symbol: K This is 0 K, which is approximately -273 °C, or -460 °F.

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Next > Amount of substance (n) The mole is the amount of substance of a system that contains exactly × specified elementary entities, which may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. Standard unit: mole Symbol: mol

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Next > Electric Current (I) The ampere is the electric current in the direction of the flow of exactly × elementary charges per second. 1 mA = A 1μA = A 1 nA = A Standard unit: ampere Symbol: A

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Next > Light Intensity (I v ) The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. A normal candle emits roughly 1 cd. Standard unit: candela Symbol: cd A 100 W incandescent light bulb emits about 120 cd.

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Question 1 Which of the following is the SI unit of length? A) second B) meter C) ampere D) candela Next >

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Question 1 Which of the following is the SI unit of length? A) second B) meter C) ampere D) candela

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Question 2 Which of the following is the SI unit of current? A) second B) meter C) ampere D) candela Next >

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Question 2 Which of the following is the SI unit of current? A) second B) meter C) ampere D) candela

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Next > The SI System – Derived Units All other units are called derived units in the SI system, and these are based on the seven fundamental base units. Quantity Symbol Unit Unit Symbol Derivation Force l newtonNkg·m/s 2 EnergyEjoulejN·m = m 2 ·kg/s 2 VoltageVvoltVJ/C = m 2 ·kg/s 3 ·A Charge QcoulombCs·A FrequencyFhertzHz1/s Power P wattWJ/s = m 2 ·kg/s 3 Radiation dose D grayGvGv J/kg = m 2 /s 2

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Next > The SI System – Prefixes The SI system also uses a set of standard prefixes to represent multiples of units or sub divisions of units. MultiplesNamedecakilomegagigaterapeta SymboldakMGTP Factor DivisionsNamedecimillimicronanopicofemto Symboldmμnpf Factor Examples: 1 km = 1000 m 1 GW = 1,000,000,000 W Examples: 1 mA = A 1 nm = m

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Question 3 Which is the largest amount of energy? A) 2300 J B) 2.3 GJ C) 230 MJ D) 23 kJ Next >

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Question 3 Which is the largest amount of energy? A) 2300 J B) 2.3 GJ C) 230 MJ D) 23 kJ

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Question 4 Which is the smallest amount of force? A) 8.4 mN B) 0.84 μN C) 8.4 nN D) 8.4 N Next >

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Question 4 Which is the smallest amount of force? A) 8.4 mN B) 0.84 μN C) 8.4 nN D) 8.4 N

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how the SI system of units is based on 7 fundamental base units, from which all other units can be derived In this presentation you have seen: End > Summary the prefixes used to describe multiples of subdivisions of units

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