Measuring Matter Chapter 14-2 pp

Why do scientists measure matter? Measuring matter is another way scientists can describe matter. Measuring matter is another way scientists can describe matter. It allows them to discover more properties of a substance. It allows them to discover more properties of a substance.

What do scientists use to measure matter? Scientists use a system of units called the Scientists use a system of units called the International System of Units, or SI. This is also known as the metric system International System of Units, or SI. This is also known as the metric system This is used internationally making it a universal standard of measurement This is used internationally making it a universal standard of measurement The United States uses the U.S. standard (e.g. feet, inches, miles, etc.). Only the U.S. uses this, so it is not universal. The United States uses the U.S. standard (e.g. feet, inches, miles, etc.). Only the U.S. uses this, so it is not universal.

Types of Measurement Mass Mass Weight Weight Volume Volume Density Density

Mass Measures HOW MUCH MATTER an object contains. Measures HOW MUCH MATTER an object contains. The SI unit for mass is the KILOGRAM (kg). The SI unit for mass is the KILOGRAM (kg). For example, if you weigh 90 pounds on Earth, your mass is approximately 40 kg. For example, if you weigh 90 pounds on Earth, your mass is approximately 40 kg. 1 kg = 2.2 lbs 1 kg = 2.2 lbs Instruments you might use: balance or scale. Instruments you might use: balance or scale.

Weight Weight is different from mass. Weight is different from mass. WHY?? Weight is a measure of the FORCE OF GRAVITY on an object. WHY?? Weight is a measure of the FORCE OF GRAVITY on an object. Weight = mass (kg) x acceleration of gravity (9.8 m/s 2 ) Weight = mass (kg) x acceleration of gravity (9.8 m/s 2 ) If a person’s mass is 40 kg, his weight would equal 40 kg x 9.8 m/s 2 = 392 N. If a person’s mass is 40 kg, his weight would equal 40 kg x 9.8 m/s 2 = 392 N. N stands for Newton, which is a unit of FORCE. N stands for Newton, which is a unit of FORCE. The weight is different on Earth than it is on the moon or other planets because the force of gravity is different. The weight is different on Earth than it is on the moon or other planets because the force of gravity is different.

Volume Volume measures the AMOUNT OF SPACE matter occupies Volume measures the AMOUNT OF SPACE matter occupies There are different ways to measure volume: There are different ways to measure volume: Rectangular objects meet the standard volume formula: length x width x height Rectangular objects meet the standard volume formula: length x width x height E.g. Volume = 3 cm x 3 cm x 3 cm = 27 cm 3 E.g. Volume = 3 cm x 3 cm x 3 cm = 27 cm 3 Liquids are measured in milliliters (mL) or liters (L) Liquids are measured in milliliters (mL) or liters (L) It is important to remember that It is important to remember that 1 mL = 1 cm 3

More volume measurements What happens if you have an irregular object such as a rock? How do you find its volume? What happens if you have an irregular object such as a rock? How do you find its volume? 1. Fill a graduated cylinder with water. Measure the volume of water. 2. Place the object inside the graduated cylinder with the water. Measure the volume. 3. Subtract the original volume from the resulting volume. The difference equals the volume for the object.

Water level Water rock BEFOREAFTER

What’s next?? Now that you know how to measure mass and volume, you have the two things needed to measure DENSITY. DENSITY is a characteristic property used to identify substances. Different substances will have different densities. So, let’s take a look at what DENSITY is…

Density Density is the measurement of how much MASS is contained in a given VOLUME. In other words, you would divide the mass by its volume: Density is the measurement of how much MASS is contained in a given VOLUME. In other words, you would divide the mass by its volume: Density = Mass/Volume The units for density can vary, but the typical unit used is “grams per cubic centimeter,” or g/cm 3 However, you can use any unit of mass and divide it by any unit of volume. The density of water is 1.0 g/cm 3.

Example From Sample Problem pg. 451 in the text: A small block of wood floats on water. It has a volume of 25 cubic centimeters and a mass of 20 grams. What is the density of the wood? A small block of wood floats on water. It has a volume of 25 cubic centimeters and a mass of 20 grams. What is the density of the wood? Step 1: What do you know? Step 2: Write the formula. Step 3: Substitute what you know into the formula. Step 4: Solve. Don’t forget the correct units.

What do you know? Mass = 20 grams (g) Mass = 20 grams (g) Volume = 25 cubic centimeters (cm 3 ) Volume = 25 cubic centimeters (cm 3 )

Write the formula. Density = mass/volume

Substitute what you know into the formula. If mass = 20 g, and volume = 25 cm 3 Density = mass/volume Density = 20 g/25 cm 3

Solve… Density = 0.8 (don’t forget the units!!!) Density of the wood = 0.8 g/cm 3

Your assignment… Cornell Notes for pages Cornell Notes for pages Sample Problems p. 451 #1 & 2 Sample Problems p. 451 #1 & 2