si units in this presentation you will: explore international system (si) units next >

SI Units

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

Next >

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.

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.

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.

QuantityQuantitySymbol

UnitUnit

Symbol

Length l meter m

Mass m kilogram kg

Time t second s

Temperature T or kelvin K

Amount of substance n mole mol

Electric current I ampere A

Luminous intensity Iv candela cd

Next >

Length (l)

Standard unit: meter

Symbol: mThe 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 = 0.001 m

1μm = 0.000001 m

1 nm = 0.000000001 m

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 kg1 g = 0.001 kg1 mg = 0.000001 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.

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 cesium133 atom.

1 min = 60 s1 hour = 3600 s1 ms = 0.001 s1 μs = 0.000001 s1 ns = 0.000000001 s

Standard unit: second

Symbol: s

Next >

Temperature (T or q)

The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16

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.

Next >

Amount of substance (n)

The mole is the amount of substance of a system that contains exactly 6.0221418 × 1023 specified elementary entities, which may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.

Standard unit: mole

Symbol: mol

Next >

Electric Current (I)

The ampere is the electric current in the direction of the flow of exactly 6.242 × 1018 elementary charges per second.

1 mA = 0.001 A

1μA = 0.000001 A

1 nA = 0.000000001 A

Standard unit: ampere

Symbol: A

Next >

Light Intensity (Iv)

The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 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.

Question 1

Which of the following is the SI unit of length?

A) second

B) meter

C) ampere

D) candela

Next >

Next >

Question 1

Which of the following is the SI unit of length?

A) second

B) meter

C) ampere

D) candela

Question 2

Which of the following is the SI unit of current?

A) second

B) meter

C) ampere

D) candela

Next >

Next >

Question 2

Which of the following is the SI unit of current?

A) second

B) meter

C) ampere

D) candela

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.

QuantityQuantitySymbol

UnitUnit

SymbolDerivation

Force l newton N kg·m/s2

Energy E joule j N·m = m2·kg/s2

Voltage V volt V J/C = m2·kg/s3·A

Charge Q coulomb C s·A

Frequency F hertz Hz 1/s

Power P watt W J/s = m2·kg/s3

Radiation dose D gray Gv J/kg = m2/s2

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.

Multiples Name deca kilo mega giga tera peta

Symbol da k M G T P

Factor 101 103 106 109 1012 1015

Divisions Name deci milli micro nano pico femto

Symbol d m μ n p f

Factor 10-1 10-3 10-6 10-9 10-12 10-15

Examples: 1 km = 1000 m1 GW = 1,000,000,000 W

Examples: 1 mA = 0.001 A1 nm = 0.000000001 m

Question 3

Which is the largest amount of energy?

A) 2300 J

B) 2.3 GJ

C) 230 MJ

D) 23 kJ

Next >

Next >

Question 3

Which is the largest amount of energy?

A) 2300 J

B) 2.3 GJ

C) 230 MJ

D) 23 kJ

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 >

Next >

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

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