Measurement Systems

Measurement Systems

• Suppose the label on a ball of string indicates that the length of the string is 150.

• Is the length 150 feet, 150 m, or 150 cm?

• For a measurement to make sense, it must include a number and a unit.

1.21.2Standards of MeasurementStandards of Measurement

International System of Units

1795: In France, a bunch of world-

renowned scientists got together and

decided on a standard system of units.

(Le Système International d’Unités)

Volume liter L

Any combination of these units creates a derived unit.

MeasurementAccurate measurements are a basic

requirement in science. A standard is an exact quantity people agree

to for comparison.

Standards define each unit.Mass of a kilogram is compared to the international prototype kilogram made of

platinum alloy

MassThe kilogram (kg) is the SI unit of mass.

1 kg = 2.205 pounds

Measured using a balance/scale

The meter (m) is the SI unit of length. It is defined as the length of the path travelled by light in a vacuum during a time

interval of 1/299,792,458 of a second .

How many cm are in 1 m?

Length is the distance between two points.

Measuring Distance

VolumeThe SI unit for volume is the liter (L).

V = l x w x hLiquid volumes are measured using a graduated

cylinderSolid volumes are found by multiplication

1 mL = 1cm3

Density

Density is the mass of a material divided by its volume.

substance density (g/cm3)

water 1.0

aluminum 2.7

lead 11.3

mercury 13.6

gold 19.3

D=mV

The measurement unit for density: g/cm3 (a combination of SI units = a derived unit)

1.21.2Standards of MeasurementStandards of Measurement

What’s Hot and What’s Not

Temperature is the measure of how much heat something contains.

1.21.2Standards of MeasurementStandards of Measurement

For most scientific work, temperature is measured on the Celsius (C) scale, where the freezing point of water is 0C, and the boiling point of water is 100C.

Time and TemperatureThe SI unit for time is the second (s).

The SI unit for temperature is kelvin (K).

degrees Celsius + 273 = kelvins

Fahrenheit = 1.8C + 32

At what temperature does water freeze on the Kelvin scale? At what temp does it boil?

273 K, 373 K

Question 1

1.21.2Section CheckSection Check

A __________ is an exact quantity that peopleagree to use to compare measurements.

A.) variableB.) standardC.) unitD.) control

SI standards are universally accepted and understood by scientists throughout the world.

B!

Question 2

1.21.2Section CheckSection Check

The amount of space occupied by an object iscalled _________?

The answer is volume. To find the volume of asolid rectangle, measure the rectangle’s lengthby its width by its height.

Answer