MEASUREMENT

SI UNITS

• These are the units that scientists use when they are measuring things.

• We will use them in this class

• You’ve heard of them before.

Length, width, height, or distance:

• The basic SI unit of length is the meter (m).

• 1 Meter is about the distance from the floor to the doorknob on a door.

• Use a meter stick to measure length.

METER STICK1 cm 1 mm

METER STICK

1 Meter = 100 cm = 1000 mm

10 mm

1 cm

1/10 m

WHEN MEASURING LENGTH

Mass

• Amount of matter (stuff) something contains.

• The basic SI unit of mass is the Kilogram (kg).

• 1 kilogram is about the mass of a wooden baseball bat.

• Use a triple-beam balance to measure mass.

12

3

First move big rider, then middle rider, then small rider.

WHEN MEASURING MASS

MASS vs. WEIGHT

• Mass – Amount of matter (stuff) something contains.

• Weight – Amount of matter (stuff) something contains + GRAVITY.

• The weight of an object depends upon where the object is located because gravity changes with where you are. The mass of an object does not change. If you were on the moon, your weight would change, but your mass would stay the same.

HOW COULD SOMEONE CHANGE THEIR MASS?

VolumeHow much space an object takes up.

The basic SI unit of volume for liquids is the liter (L).

The basic SI unit of volume for solids is the cubic centimeter (cm3)

Use a graduated cylinder to measure volume of a liquid

Use a meter stick to measure length, width, height to measure volume of a solid

Measuring volume

LIQUID SOLID

V = L X W X H

VERY IMPORTANT !!

1mL = 1cm3

This gives us a relationship betweenvolume of a liquid and volume of a solid

Volume

TO MEASURE THE VOLUME OF A SOLID THAT IS SHAPED WEIRD:

Place the object in water. Measure the volume of the water before you put the object in and measure the volume after you put the object in. Subtract the volumes and the difference is the volume of the object.

How do we measure the volume of a grape?

Volume of something shaped weird

41mL – 35mL = 6 mL or 6 cm3

What is density?Tells how airy a substance is. It relates mass and

volume together

The density of a substance is the same for all pure samples of that substance.

Example: all samples of gold have a density of 19.3 g/cm3 . You can tell fake gold from real gold by measuring the densities.

The basic SI units of density for solids are: grams per cubic centimeter (g/cm3)

The basic SI units of density for liquids are: grams per milliliter (g/mL).

VERY IMPORTANT!!

Density = m / v

Density units = depend uponunits of volume used.

g/cm3 g/mLsolid liquid