International System of Units“Systeme International” (SI), Conversions, density and volume

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Context and definitionMain Standards of Measurement:

◦The United States Customary System (USCS), formerly called the British system of units. The USCS is used today in the U.S.A. and Burma.

◦The Systeme International (SI) is also known as the international system and the metric system. This system is practically used worldwide.

Each system has its own standards of length, mass, and time, which are the fundamental units.

Taken form Hewitt’s “Conceptual Physical Science”

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The USCSThe USCS is based on the British Imperial

System. It is used by most people in the U.S.A.

It uses the foot as the standard of length, the pound as the unit of force or weight, and the second as the unit of time.

It is slowly being replaced by the International System, particularly in science and technology.

Length unit, the foot, probably defined after Henry I of England. Problem is inconsistency.

Taken form Hewitt’s “Conceptual Physical Science”

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The International System (SI)In 1960 at a conference in Paris, the SI units

were defined.The SI is based on the metric system,

originated by French scientists after the French Revolution.

The system is logical, and it is widely applied by scientists and others all around the world.

In physics, common units are meters (m), kilograms (kg), and seconds (s).

The metric system uses the decimal system, where all units are related by dividing or multiplying by 10.

Taken form Hewitt’s “Conceptual Physical Science”

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The San Juan de Dios Radiology accident How long is 0,3 minutes? It is NOT 30 seconds 0,3 minutes (60 seconds/1

minute) are 18 secondsPatients were exposed to 30

seconds of radiation instead of 18 as a result of an incorrect conversion

Many patients died as a resultTaken form Hewitt’s “Conceptual Physical Science”

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The Most Common Units – the Metermeter (m): Standard of length. Originally defined in terms of the

distance from north pole to the equator. This distance was thought to be 10,000,000 meters.

The meter was carefully marked in a metal bar that is kept at the International Bureau of Weights and Measures in France.

The meter now is calibrated in terms of the wavelength of light.

Taken form Hewitt’s “Conceptual Physical Science”

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The Most Common Units – the Kilogramkilogram (kg): Standard unit of mass.

One gram is the mass of 1 cubic centimeter (cc) of water at a specific temperature. The kg equals 1000 grams.

The kg is a block of platinum-iridium alloy preserved at the International Bureau of Weights and Measures in France.

Taken form Hewitt’s “Conceptual Physical Science”

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The Most Common Units – the Secondsecond (s): Standard unit of time. Until 1956 it was defined in terms of

the solar day (divided into 24 hours, 60 minutes per hour, 60 seconds per minute).

This measure became unsatisfactory, because the rotation of earth is changing.

Now a second is the time it takes a cesium atom to make X number of vibrations

Taken form Hewitt’s “Conceptual Physical Science”

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The Most Common Units – the NewtonNewton (N): Standard unit of force or weight.

Capital N as it is named after person, scientist Sir Isaac Newton.

One newton (N) is the force required to accelerate 1 kilogram at 1 meter per second per second.

Taken form Hewitt’s “Conceptual Physical Science”

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The Most Common Units – the KelvinKelvin (K): Standard unit of

temperature. Capital K as it is named after person,

scientist Lord Kelvin. One kelvin equals one celsius degree.

Zero kelvin degrees is the absolute zero temperature.

Absolute zero is the lowest possible temperature, at which point the atoms transmit no thermal energy (it is at -273.15 Celsius or 0 K.

Taken form Hewitt’s “Conceptual Physical Science”

Taken form Hewitt’s “Conceptual Physical Science”

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T.1 – Fundamental SI Magnitudes

Magnitude Unit Symbol

Length Meter m

Mass Kilogram kg

Time Second s

Electric current Ampere A

Temperature Kelvin K

Quantity of substance Mole mol

Luminous intensity Candela cd

Taken form Hewitt’s “Conceptual Physical Science”

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T.2 – Some Derived SI Magnitudes

Magnitude Unit Symbol

Area Square meter m2

Volume Cubic meter m3

DensityKilogram per cubic meter kg/m3

Speed and Velocity Meter per second m/s

AccelerationMeter per square

second m/s2

Force and Weight Newton (kg*m/s2) N

Energy, Heat and Work Joule J

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Fundamental and Derived Units

Fundamental Units: are the units of the basic physical magnitudes, from which any other unit can be expressed.

Derived units: are the units used to measure the derived physical magnitudes. They are the product of relating two or more fundamental units.

Taken form Hewitt’s “Conceptual Physical Science”

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Fundamental and Derived Units

Only seven magnitudes are fundamental, and the others can then be derived from these.

Area, a derived magnitude, is the square of a length unit, such as square meter (m2).

Volume of object refers to the space it occupies. The unit for volume is the space occupied by a cube with sides of 1 meter (m3), or 1 cubic cm (cm3) .

Speed=distance/time is also a derived unit.

The Newton is expressed in kg * m/s2 and it is derived.

Taken form Hewitt’s “Conceptual Physical Science”

Taken from Holt's Physical Science

Derived Units: Area and Volume

Area is measured in square meters (m2). Area of rectangle is calculated by multiplying its sides.

Volume is the amount of space that something fills. Liquid volume is given in liters (L). One cubic meter (1 m3 ) equals 1000 L. You can fit 1000 L exactly into a box that is 1 m on each side.

SI unit for volume: cubic meter (1 m3). Liter is more often used. Small volumes are measured in milliliters (ml).

Taken from Holt's Physical Science

Density and Mass

Density is a measure of how much matter is in a given volume. It cannot be measured directly, as it is a derived quantity because you must calculate it from other known quantities.

Density = Mass/VolumeMatter is anything that has mass and

takes up space (a phone, a person, air all have matter)

The amount of space that an object takes up is known as the object’s volume.

Taken from Holt's Physical Science

Measuring Volume

Volume of regularly shaped solid object: Measured in cubic units, multiplying length, width, and height.

What is the difference between area and volume? A cube has volume, a square only has area.

What is volume of box with area of 400 cm2 and height of 10 cm? V = 400 cm2 x 10 cm = 4000 cm3

Taken from Holt's Physical Science

Measuring Volume

Volume of irregularly shaped object: you can put object into a known volume of water. The increase in volume is equal to the volume of the object.

Objects cannot occupy the same space at the same time.

Meniscus: curve of the surface of a liquid. The amount of liquid in a container is measured from the lowest point of the meniscus.