- Slides: 15
The Scientific Method
“Science is the pursuit of knowledge and understanding of the natural and social world following a systematic methodology based on evidence. ” - Britain’s Science Council, www. sciencecouncil. org � pursuit of knowledge vs. body of facts � based on evidence � systematic methodology ◦ the scientific method
The Scientific Method � the general process used by scientists to establish accurate understanding of the world � traditionally represented as linear
Can be more accurately represented as a cycle: e r e St h t ar
Theory: My car is out of gas. Experimental: Observation: Prediction: My car won’t start. My car still won’t start. If. . . then. . Experiment: Experiment I fill my car with gas, and try to turn it on. Analyze the experimental outcome: ØWas my prediction correct? ØDoes this outcome support or refute my theory?
Experimental design Scientists rely on properly-designed experiments to establish cause-and-effect relationships A leads to B
Elements of a good scientific experiment: 1. singularity – it tests the effect of only one factor (A) on another (B) 2. reliability & reproducibility – it can be repeated by other scientists to obtain similar results 3. utility – it is useful to humankind in some way
Experimental Variables �a variable is any factor that can be controlled, changed, or measured ◦ independent variable – manipulated ◦ dependent variable – measured ◦ controlled variable – kept constant; might also have an effect on the DV Cause Effect The experimenter manipulates/alters the A second variable is observed/measured – the independent variable (IV) What is the effect of the IV on the DV? dependent variable (DV)
Independent the liquid used to water each plant Dependent the height or health of the plant Controlled type of plant, amount of liquid, pot size, soil type, etc.
Some experiments also incorporate a Control Group. �…a group of subjects that are not altered in any way. ◦ no effect should be observed example: Controlled pharmaceutical study Treatment Group Control Group
Control group should have similar composition as the experimental group. ◦ allows direct comparison ◦ provides support that any observed effects are not just due to random chance Treatment Group • 250 males • age 35 -45 • active lifestyle Control Group • 250 males • age 35 -45 • active lifestyle
Example (1) The speed of a chemical reaction depends on a number of factors. These factors include the amount of chemicals reacting, and the temperature at which they react. In an experiment studying a particular chemical reaction, the temperature is increased by 5°C each time the reaction is performed. a) What is the independent variable? b) What is the dependent variable? c) Identify at least one variable that must be controlled in this experiment.
Example (2) An experiment is set up to measure the time that a pendulum takes to swing back and forth 20 times. The pendulum consists of an object at the end of a string, and it is released from a certain height above the lowest point in the pendulum's path. The length of the string is shortened by 5 cm and the time is measured. a) What is the independent variable? b) What is the dependent variable? c) Identify at least one controlled variable for this experiment.
Example (3) You are a scientist studying the long-term effects of reduced gravity on the bones of astronauts. The astronauts’ bone density is recorded before they go into orbit, and is recorded again upon their return. Different groups of astronauts spend different amounts of time in space aboard the same space station. a) What is the independent variable? b) What is the dependent variable? c) The astronauts go to a single space station. How does this serve as a control? d) Explain how a similar group of astronauts who remain on Earth during the same time period serves as a control group.
Your turn… Design a controlled experiment to test the absorbent power of two different brands of paper towel. Identify each of your variables: 1. a) b) c) 2. independent variable + how it will be measured controlled variables Is a control group necessary?