Chapter 1 Introduction to Physical Science Section 1-3:Measurement • Why do scientists use a standard measurement system? • What are the SI units of measurement for length, mass, volume, density, time, and temperature?
Chapter 1 Introduction to Physical Science A Standard Measurement System • Using SI as the standard system of measurement allows scientists to compare data and communicate with each other about their results. SI units are based on multiples of 10. We will be using SI and other metric units.
The Metric System • The SI system is considered to be the modern metric system. • It is considered a universal language for scientists, doctors, the military, and most countries. • The US is one of the only countries not on the metric system. • We use The English System which includes mph, feet, pounds, gallons, Farenheit, etc.. Why do you think the US has not switched to the Metric System?
Chapter 1 Introduction to Physical Science Length • The basic unit of length in SI is the meter (m). • To measure something larger than a meter, scientist may use kilometers (km), which means one thousand. • To measure something smaller than a meter, scientists may use centimeters (cm), centi- means one-hundredth, or millimeters (mm), milli- means one-thousandth.
Consider a ruler • This ruler shows both Metric and English units for measuring length • The numbers on the top are centimeters • The tiny lines within each centimeter are millimeters. • Notice there are 10 mm in 1 cm. COUNT THEM! • How many mm are in 3 cm? • The numbers on the bottom are inches • Notice how much bigger 1 in is compared to 1 cm • There are 2.54 cm in 1 in • We will practice converting from Metric to Metric and from Metric to English later!
WEIGHT vs MASS Weight: Mass: Mass is the measure of the amount of matter an object contains. Mass is not affected by gravity. If you travel to the moon, the amount of matter in your body (your mass) will not change. Scientists prefer to use mass rather than weight. SI unit of mass is the kilogram (kg), but we will be using mostly grams (g) in this class. WHY? • Your weight is a measure of the force of gravity on you. • The force of gravity may be more or less on other planets or moons than on Earth. • You would weigh about one-sixth of your Earth weight on the moon. • The newton (N) is the SI unit, the pound (lb) is the English unit.
Chapter 1 Introduction to Physical Science Volume • Volume is the amount of space an object takes up. • The SI unit of volume is the cubic meter (m3), but we will often measure in Liters (L) or millileters (mL).
Volume of a liquid: • Graduated cylinder • mL • Meniscus- curved surface at top of liquid, always record measurements using bottom of meniscus
Volume of Rectangular Solid: Volume of Irregular solid: • Example- Cereal box • Volume = Length x Width x Height • Remember to multiply numbers and units, so units will be cubed • Example units: cm3 • Example- Rock • Submerge object in water in graduated cylinder and measure the displacement of the water • Let’s look at the example in your book on page 23 now
Density • Two objects of the same size can have very different masses. WHY??? • Because different materials have different densities! • Density is mass per unit volume • So Density = Mass/ Volume • SI unit of density is kg/m3, other common units are g/cm3 and g/mL • Since density is made up of 2 measurements, it always has 2 units
Suppose that a metal object has a mass of 57 g and a volume of 21 cm3. Calculate its density. Read and Understand What information are you given? Mass of metal object = 57 g Volume of metal object = 21 cm3 Chapter 1 Introduction to Physical Science Calculating Density
Suppose that a metal object has a mass of 57 g and a volume of 21 cm3. Calculate its density. Plan and Solve What quantity are you trying to calculate? The density of the metal object = __ What formula contains the given quantities and the unknown quantity? Density = Mass/Volume Perform the calculation. Density = Mass/Volume= 57g/21cm3 = 2.7 g/cm3 Chapter 1 Introduction to Physical Science Calculating Density
Suppose that a metal object has a mass of 57 g and a volume of 21 cm3. Calculate its density. Look Back and Check Does your answer make sense? The answer tells you that the metal object has a density of 2.7 g/cm3. The answer makes sense because it is the same as the density of a known metal–aluminum. Chapter 1 Introduction to Physical Science Calculating Density
Practice Problem What is the density of a wood block with a mass of 57 g and a volume of 125 cm3? 0.46 g/cm3 Chapter 1 Introduction to Physical Science Calculating Density
Chapter 1 Introduction to Physical Science Density • The density of a substance stays the same no matter how large or small a sample of the substance is. • So a gold earring and a gold necklace will both have a density of 19.3 g/cm3
Sink or Float? • Knowing an object’s density allows you to predict whether it will sink or float. • If the object is less dense than the liquid, it will float. • If the object is more dense than the liquid, it will sink. FLOAT! Problem: Water has a density of 1 g/cm3. Will an object with a density of 0.7 g/cm3 float or sink in water?
Chapter 1 Introduction to Physical Science Time • The second (s) is the SI unit of time.
Chapter 1 Introduction to Physical Science Temperature • Scientists use the Celsius and Kelvin scales to measure temperature. The kelvin (K) is the SI unit of temperature.