Finish questions #2-5 that you copied down during DSW last class.
Methods of Science
The job of a scientist is to observe and explain the natural world. Many observations do not have an obvious explanation, so scientists generate hypotheses, or potential explanations, and test them with experiments.
A good scientist considers all the factors that might be responsible for what he or she observes. Factors that can vary and that we can measure are called variables; examples of variables include temperature, time, water level, number of organisms, and so on. We can investigate the role of a specific variable by keeping all other variables constant while changing the variable we are testing and then observing what happens. This process is called a controlled experiment. For example, we might hypothesize that fish swim slowly at night because the water becomes cool. In a controlled experiment, we would examine the swimming speed of fish at different temperatures. The variable that we change, in this case water temperature, is called the independent variable. The variable that we think is affected by the independent variable, in this case swimming speed, is called the dependent variable. We could also hypothesize that fish swim more slowly at night because it's dark, and we would then examine the influence of light level (an inde¬pendent variable) on swimming speed (the dependent variable).
THINK ABOUT IT
1. Why don't scientists try to test many variables in a single experiment?
WRITING HYPOTHESES
Hypotheses are critical to scientific investigation because they form the bases of our experimental design. Writing good hypotheses can be trickier than you think. We can make a number of statements about fish swimming speed that can be inter¬preted in different ways by changing just a few words. For example, consider the following:
• Fish swam slowly last night.
• Cold temperatures caused fish to swim slowly last night.
• Fish swimming speed is influenced by temperature: at cool nighttime tempera¬tures they swim more slowly than at warmer daytime temperatures.
Each statement includes references to fish swim speed and temperature. How¬ever, each statement has its own meaning and only one can be considered a hypothesis. The first is not a hypothesis because rather than stating an explanation, it simply states two facts: (1) fish swam slowly and (2) it was nighttime what happened (fish swam slowly because it was cool);
it states this explanation as an indisputable fact and is therefore not testable. Only the last statement is a hypothesis. It proposes an explanation for the swim speed of fish at night (temperatures are cooler), and it is testable because we can put fish in water of different temperatures and observe their swim speed.
A good hypothesis clearly states what variable we want to test and predicts it effect. It is not important if your hypothesis turns out to be right or wrong. What matters is that you can test it and draw an appropriate conclusion based on your data.
CONVERTING QUESTIONS TO HYPOTHESES
Below are some questions about the environment. Read them, and identify what variables can be controlled (independent) and what variables will be observed (dependent). Rewrite each question as a hypothesis. Double-underline the independent variable. and single underline the dependent variable. Your hypothesis should clearly state the predicted response of the dependent variable when the independent variable is manipulated. The independent variable can be increased, decreased, or even removed during the experiment.
For example, the question, "Is the rate at which a substance gains or loses heat related to its density?" can be restated as the hypothesis, "The more dense substance is, the faster it will gain heat." Other possibilities are equally valid for example, "the more dense a substance is, the more slowly it will gain heat,"
2. Question: How does the amount of energy that hits the Earth in the form of light rays relate to the angle at which those rays strike (latitude)?
3. Question: Does rainfall influence the distribution of different biomes such deserts, grasslands, and forests? '
4. Question: Does the extinction of a predator species result in a faster rate population growth in the prey species?
5. Question: Is plant cover related to soil erosion?
