An object's size and weight are both measurable. We can also measure such things as how far, how much, and how hot or cold. Even when and where are measurable. Although these measurements are different from one another, they all have something in common. Each one relates to a specific set of units that people have agreed upon.

France first adopted the metric system in 1795. Today, people in most countries use this system.

The Metric System

The metric system is a group of measurement units. All of its units, large and small, are built by using multiples of 10. This system is very useful to scientists because each unit is connected. For instance, the base unit of length is the meter. A kilometer equals 1,000 meters. Likewise, a kilogram equals 1,000 grams. Grams are the units used to measure weight.

Measuring Temperature

A thermometer is an instrument for measuring temperatures of different gases, liquids, and solids. There are many types of thermometers. One common type is the thermal expansion thermometer.

Thermal expansion thermometers have a long glass tube with a bulb at the base. Sealed inside the tube is liquid mercury. When the temperature goes up, the mercury expands and rises up the tube. When the temperature gets lower, the mercury contracts. The mercury sinks back down.

Today, some thermometers do not contain mercury because it is poisonous. They may use alcohol instead.

The marks on the outside of the tube are the temperature scale. This scale gives a value to the mercury's changing height. The value, or mark, relates to the scale used.

Weather Thermometer

Clinical Thermometer

Laboratory Thermometer

Different Temperature Scales

Some thermometers use two different temperature scales: Celsius and Fahrenheit. Anders Celsius and Gabriel Fahrenheit were their creators. Both men lived in the 1700's.

The two most important points on these scales are the freezing point and boiling point of water. The Celsius scale makes 0° the point at which water freezes. Water's boiling point is 100° on this scale. The difference between the two points is 100°. The Fahrenheit scale makes 32° as water's freezing point and 212° as its boiling point. The difference between the two points is 180°.

Scientists around the world use the Celsius scale. Its 100-point system fits in with the metric system.

The Celsius and Fahrenheit scales differ in the units used to measure the mercury's rise and fall.

Measuring Weight

Weighing devices have been around a long time. The earliest type, called a balance, was popular in ancient Egypt 4,500 years ago. Even today, scientists use balances for weighing light materials.

The two pan balance is one of many different types of balance scales.

Using an Equal-Arm Balance

This type of balance is useful in making sure that two materials weigh the same. It has a horizontal bar that holds a hanging pan at each end. The user places one material with a known weight in the first pan. The other material goes in the second pan. If the first pan is heavier, it will drop down.

To reach an equal weight, the user adds more material to the second pan. Eventually, neither pan drops lower than the other. Usually a pointer shows if the pans are balanced. If so, the materials weigh the same amount.

In an equal arm balance, a piece of metal often supports the center of the horizontal bar.

Triple Beam Balance

Another common weighing device is the triple beam balance. This mechanical scale weighs objects differently. However, it is still a balance because its job is to balance different weights.

Triple Beam Balance Scale

TRY THIS

STEP?1

To weigh something, the user first slides the three moveable weights (called poises, or riders) to the left side of the beams. The pointer should be at the zero mark on the scale.

STEP?2

Then the user places the object in the pan. The pointer will move away from zero. By moving the two heavier weight riders, then the lightest one, to the correct positions, the pointer will return to zero. Now the load is balanced.

STEP 3

To read the object's weight in grams, the user adds up the three numbers marked by the riders.

Spring scales also are a type of mechanical scale. They balance a load by using one or more springs.

Spring Scale

Today's electronic scales weigh objects very precisely.

Electronic Scale

In the Laboratory

Scientists do a lot of work in the lab. There, they can carefully study objects and materials gathered in the field. The lab is also a useful place for conducting experiments and testing out ideas.

Typical Lab Tools

filter paper

round-bottom flask

test tube, test tube rack, test tube holder

funnel

liquid eyedropper

graduated cylinder

Bunsen burner

gas jar

Petri dish

beaker

Erlenmeyer flask

evaporating dish

What Makes Up a Mixture?

When scientists want to study the parts of a mixture, they need advanced equipment. One machine called a centrifuge separates liquid mixtures.

Centrifuges spin from 800 to 6,000 times per minute.

It also separates solids within a liquid. The centrifuge does its job by rotating the containers that hold the mixtures. This causes the different substances to move apart. Each has a different density.

Lab Safety

Laboratory work often involves chemicals, glass, and open flames. That's why it helps to follow safety procedures. Scientists of all ages learn how to set up lab equipment, and use it properly. They also have training in how to conduct experiments in a careful, step-by-step way. This ensures safety in the lab and that results from experiments are not accidental.

Accidents happen in the lab. So it's helpful to know where safety equipment is stored. Knowing the location of the fire alarm and emergency exit are important, too.

Chemistry Experiments

Scientists working with chemicals know that these materials can be dangerous. To limit the danger, chemists read all labels. They also know how to dispose of chemicals and transfer them from place to place.