Designing an Experiment Lesson 1.3 Chapter 1: Using Scientific Inquiry Interactive Science Grade 8, Pearson Education Inc., Upper Saddle River, New Jersey

This build up of salt on the soil surface is called salinization. This is a very big problem in the desert and prairie biomes. This can cause physical soil damage, and the ability to grow plants. Causes a reduction of plant growth due to high salt content in the soil is related in part to osmotic effects and also to the specific ions involved (Na +, Mg 2+, Ca 2+, K +, Cl -, SO 4 2-, HCO 3 -, and CO 3 2- ).

Definitions Scientific inquiry – the process of gathering evidence about the natural world and proposing explanations based on this evidence. Hypothesis (plural: hypotheses) – is a possible answer to a scientific question. Also a possible explanation. Independent variable – in an experiment, one factor that is purposely changed to test a hypothesis.

Dependent variable – in an experiment, the factor that may change in response to the independent variable. Controlled experiment – a scientific experiment in which only one variable is changed at a time. Bias – an error in the design of an experiment that may give misleading results.

International system of units (SI) – a system of units used to measure the properties of matter, to collect and record quantitative data. Repeated trial – a repetition of an experiment. Replication – an attempt by a different group of scientists to repeat an experiment to verify results. Scientific explanation – a generalization that makes sense of observations by using logical reasoning.

What is Scientific Inquiry? Definition Often begins with an observation that leads to a question. Then you define a problem. Ask what is already known.

Developing a hypothesis Define hypothesis Hypotheses are not facts. A fact is an observation or description that has been confirmed repeatedly.

How Do You Design an Experimental Investigation? Controlling Variables Independent variable (manipulated, test) Dependent variable (response)

Groups and Repeated Trials Each group should have repeated trials, 30 trials ideal. Experimental group – group in which the independent variable is manipulated. Control group – group used to compare with experimental group. – All factors are kept “normal”. – No manipulation of independent variable.

Experimental Bias Can be prevented by – Randomly assigning experimental treatments. – Making sure measurements are recorded with calibrated instruments.

Collecting and Analyzing Data Use SI units Record quantitative and qualitative data in tables. Graph data and run calculations.

Interpreting Data and Drawing Conclusions Indicate whether your data supports or fails to support (rejects) your data. Relate your results to current understanding of relevant scientific knowledge.

Communicating Scientists share their results through writing and speaking. Other scientists can evaluate the research and even replicate to verify results.

What is a Scientific Explanation? A scientific explanation is a generalization that makes sense of observations by using logical reasoning. – Often necessary when experimentation cannot be done. – In which case, descriptive or comparative studies are conducted.