Observing and Inferring
Observing  Scientists try to make careful and accurate observations. When possible, they use instruments such as microscopes, thermometers, and balances to make observations. Measurements with a balance or thermometer provide numerical data that can be checked and repeated.

When you make observations in science, you'll find it helpful to examine the entire object or situation first. Then, look carefully for details. Write down everything you observe.

Examples
Imagine that you have just finished a volleyball game. At home, you open the refrigerator and see a jug of orange juice on the back of the top shelf. The jug, shown in Figure 13, feels cold as you grasp it. Then you drink the juice, smell the oranges, and enjoy the tart taste in your mouth.

As you imagined yourself in the story, you used your senses to make observations. You used your sense of sight to find the jug in the refrigerator, your sense of touch when you felt the coldness of the jug, your sense of hearing to listen as the liquid filled the glass, and your senses of smell and taste to enjoy the odor and tartness of the juice. The basis of all scientific investigation is observation.

Inferring  Scientists often make inferences based on their observations. An inference is an attempt to explain or interpret observations or to say what caused what you observed.

When making an inference, be certain to use accurate data and observations. Analyze all of the data that you've collected. Then, based on everything you know, explain or interpret what you've observed.

Examples
When you drank a glass of orange juice after the volleyball game, you observed that the orange juice was cold as well as refreshing. You might infer that the juice was cold because it had been made much earlier in the day and had been kept in the refrigerator or you might infer that it had just been made, using both cold water and ice. The only way to be sure which inference is correct is to investigate further.

Comparing and Contrasting
Observations can be analyzed by noting the similarities and differences between two or more objects or events that you observe. When you look at objects or events to see how they are similar, you are comparing them. Contrasting is looking for differences in similar objects or events.

Example
Suppose you were asked to compare and contrast the nutritional value of two candy bars, Candy A and Candy B. You would start by looking at what is known about these candy bars. Arrange this information in a table, like the one in Figure 14.

Similarities you might point out are that both candy bars have similar serving sizes, amounts of total fat, and protein. Differences include Candy A having a higher calorie value and containing more total carbohydrates than Candy B.

Recognizing Cause and Effect
After scientists organize data in tables, they may display the data in a graph. A graph is a diagram that shows the relationship of one variable to another. A graph makes interpretation and analysis of data easier. There are three basic types of graphs used in science-the line graph, the bar graph, and the circle graph.

Have you ever watched something happen and then made suggestions about why it happened? If so, you have observed an effect and inferred a cause. The event is an effect, and the reason for the event is the cause.

Example
Suppose that every time your teacher fed the fish in a classroom aquarium, she or he tapped the food container on the edge of the aquarium. Then, one day your teacher just happened to tap the edge of the aquarium with a pencil while making a point. You observed the fish swim to the surface of the aquarium to feed, as shown in Figure 15. What is the effect, and what would you infer to be the cause? The effect is the fish swimming to the surface of the aquarium. You might infer the cause to be the teacher tapping on the edge of the aquarium. In determining cause and effect, you have made a logical inference based on your observations.

Perhaps the fish swam to the surface because they reacted to the teacher's waving hand or for some other reason. When scientists are unsure of the cause of a certain event, they design controlled experiments to determine what causes the event. Although you have made a logical conclusion about the behavior of the fish, you would have to perform an experiment to be certain that it was the tapping that caused the effect you observed.