The Metric System & Scientific Data p14-25

PS-1.3PS-1.5

Why SI?

SI stands for the international system (Système International d’Unités)

This is the measurement system that is used by all scientists, worldwide

In the US, it is sometimes incorrectly called the metric system

What is SI? There are different base units which

can be found in your text on p16. Length = meter Mass = kilogram Volume = cubic meters (m3) or liters

Derived units come from combinations of base units Kilometers per hour (km/h) Square meter (m2)

What is SI?

SI prefixes indicate multiples of base units or fractions of base units. Chart on p17 in your text. Centi- means 1/100th

As in, centimeter = 1/100th meter Kilo- means 1,000.

As in, kilometer = 1000 meters

Density, a derived unit

Density is the ratio of an object’s mass to its volume Density = mass/volume

Density is why two objects can have the same volume but different mass

Scientific Data

Precision is a gauge of how exact a measurement is. 3 hours and 4 minutes is less precise

than 3 hours 4 minutes and 36 seconds

Accuracy is the closeness of a measurement to the actual value of what is being measured

Scientific Data

Scientists must organize their data in order to communicate with others Data tables and graphs are ways to

organize data Data must always include units

Significant Figures

Significant figures are all the digits that are known in a measurement, plus the last digit that is estimated. For instance, on a triple beam balance

you can read to the nearest 1/10th of a gram.

You can estimate between the 1/10th of a gram

So, you can have a measurement of 157.45 grams.

Significant Figures

So, the number 157.45 has five significant figures.

Any calculations using this number, can have no more than five significant figures as well.

Conversions

A conversion factor is a ratio of equivalent measurements that is used to convert a quantity from one unit to another.

“What did he say?”

Let’s look at one common type of conversion…

Conversions

Fahrenheit to Celsius: