economic english 6 pptx

A change is often a response to a gradient or a differ￾ence in a property in two parts of a system. Here are

some examples of common gradients and the changes

they drive.

■ Difference in temperature—causes heat to flow

from hotter object (region) to colder object

(region).

■ Difference in pressure—causes liquid (water) or

gas (air) to flow from region of high pressure to

region of low pressure.

■ Difference in electric potential—causes electrons

to flow from high potential to low potential.

■ Difference in concentration—causes matter to

flow until concentrations in two regions are

equalized.

Measurement

An established principle in science is that observations

should be quantified as much as possible. This means

that rather than reporting that it’s a nice day out, a scien￾tist needs to define this statement with numbers. By nice,

two different people can mean two different things.

Some like hot weather. Some like lots of snow. But giving

the specifics on the temperature, humidity, pressure,

wind speed and direction, clouds, and rainfall allows

everyone to picture exactly what kind of a nice day we

are having.

For the same reason, a scientist studying the response

of dogs to loud noise wouldn’t state that the dog hates it

when it’s loud. A scientist would quantify the amount of

noise in decibels (units of sound intensity) and carefully

note the behavior and actions of the dog in response to

the sound, without making judgment about the dog’s

deep feelings. Now that you are convinced that quantify￾ing observations is a healthy practice in science, you will

probably agree that instruments and units are also useful.

In the table at the bottom of the page are the most

common properties scientists measure and common

units these properties are measured in. You don’t need to

–UNIFYING CONCEPTS AND PROCESSES–

215

COMMON UNITS OF MEASURE

Length or distance meter (about a yard)

centimeter (about half an inch)

micrometer (about the size of a cell)

nanometer (often used for wavelengths of light)

angstrom (about the size of an atom)

kilometer (about half a mile)

light-year (used for astronomical distances)

Time second, hour, year, century

Volume milliliter (about a teaspoon), liter (about

1

4

of a gallon)

Temperature degree Celsius, degree Fahrenheit, or Kelvin

Charge coulomb

Electric potential volt

Pressure atmosphere, mm of Hg, bar

Force newton