Scientific MethodScientific MethodScientific MethodScientific Method

VariablesVariables

Variables• There are three kinds of variables that

you must account for in an experiment. – Independent variables – Changing –

the factor that you change in an experiment.

– Dependent variables – Response or Result – the effect of what you changed.

– Controlled Variables – Constant – the things that you do not change.

Independent Variable

The independent variable is what you change in the experiment. For instance, if you are trying to find out how much magnesium radish plants need to grow, your independent variable might be concentration of magnesium in the nutrient solution. It is important that you have only one independent variable in your experiment. For example, you cannot vary both the magnesium concentration and the temperature conditions of your radish plants. You would not be able to draw reliable conclusions from the experiment if you altered more than one experimental condition

Dependent Variable• The dependent variable is what you measure in

the experiment. Unlike the independent variable, an experiment can have several dependent variables because variations in the independent variable can have many different effects. For example, you might measure length of leaves and weight of roots to assess the growth of radish plants. Dependent variables can include qualitative as well as quantitative data: you might also examine the color of the radish leaves and eat the roots to see how they taste. Such data cannot be measured but is still useful when you describe and compare it.

Controlled VariablesAny other conditions in the experiment are called controlled variables. You must keep these conditions constant for all trials of the experiment. Controlled variables might include light exposure, humidity, pH of solution, ambient noise, type of soil, type of pot, type of plant, amount of water, etc.

If you change these variables, they become independent variables, and remember that you cannot have more than one independent variable in a scientific experiment.

Two Types of Observations

• Qualitative – describes an object or event

• Quantitative – Measures or quantifies an object or event (includes specific #s)

• Examples:• Qualitative – Jackie is wearing a bright

red shirt today.• Quantitative – Jackie is 5 feet 3 inches

tall.

You try it…•In your notebook write

three (3) qualitative observation about the classroom AND three (3) quantitative observations about the classroom.

• A group of students was interested in

the effect of color on the time balloons stayed inflated. They thought that balloons of some colors would hold air longer than balloons of other colors.

– Identify the independent variable, the dependent variable, and control variables.

Steps for Writing a Good Hypothesis

• Identify variables in a given event.• Identify a pair of variables that might be

related.• Identify the Independent Variable (IV) and

the Dependent Variable (DV).• Write the hypothesis using the following

format.• I believe if the [independent variable]

increases or decreases, then the [dependent variable] will increase or decrease.

• Smithers thinks that a special juice will increase the

productivity of workers. He creates two groups of 50 workers each and assigns each group the same task (in this case, they're supposed to staple a set of papers). Group A is given the special juice to drink while they work. Group B is not given the special juice. After an hour, Smithers counts how many stacks of papers each group has made. Group A made 1,587 stacks, Group B made 2,113 stacks.

•   • Identify the:• 1. Independent Variable• 2. Dependent Variable• 3. Controlled Variable• 4. What should Smithers' conclusion be?  • 5. How could this experiment be improved?

• 1. Independent Variable Special Juice• 2. Dependent Variable Amount of stapled papers

stacked• 3. Control Same task, same materials, same

working conditions (light, temperature, space, )• 4. What should Smithers' conclusion be? The group that

did not have the juice was more productive. So the juice was not a factor in the productivity of the workers.

•  5. How could this experiment be improved? Drink the juice fifteen minutes prior to the task. Drinking the juice during the task would have decreased the number of papers completed.

• Bart believes that mice exposed to radio waves will become

extra strong (maybe he's been reading too much Radioactive Man). He decides to perform this experiment by placing 10 mice near a radio for 5 hours. He compared these 10 mice to another 10 mice that had not been exposed. His test consisted of a heavy block of wood that blocked the mouse food. he found that 8 out of 10 of the radio-waved mice were able to push the block away. 7 out of 10 of the other mice were able to do the same.

• Identify the-11. Controlled Variable

• 12. Independent Variable • 13. Dependent Variable• 14. What should Bart's conclusion be? • 15. How could Bart's experiment be improved?

• 11. Controlled Variable – Same environment, temperature, space, food, block weight and

method of blocking food source.

• 12. Independent Variable – Radio waves

• 13. Dependent Variable– Strength to move a block

• 14. What should Bart's conclusion be? – The radio waves did not have a significant effect on the strength of

the mice.

• 15. How could Bart's experiment be improved? – The weight of the block must be the same. The distance/volume

from the radio or absence of the radio must be clear

• Krusty was told that a certain itching powder was the newest

best thing on the market, it even claims to cause 50% longer lasting itches. Interested in this product, he buys the itching powder and compares it to his usual product. One test subject (A) is sprinkled with the original itching powder, and another test subject (B) was sprinkled with the Experimental itching powder. Subject A reported having itches for 30 minutes. Subject B reported to have itches for 45 minutes.

• Identify the-16. Controlled Variable

• 17. Independent Variable• 18. Dependent Variable• 19. Explain whether the data supports the advertisements

claims about its product.

• 16. Controlled Variable– Same costume, same environment, temperature,

movement, size• 17. Independent Variable

– Two different brands of itching powder• 18. Dependent Variable

– Amount of time that the itching powder causes the subject to itch.

• 19. Explain whether the data supports the advertisements claims about its product.– The new itching powder lasted 50% longer than the

other powder.

• Lisa is working on a science project. Her task

is to answer the question: "Does Rogooti (which is a commercial hair product) affect the speed of hair growth". Her family is willing to volunteer for the experiment.

• 20. Identify the controlled variable, and the independent and dependent variables in your description

• Controlled variable – Same amount of hair product applied for the same

length of time in the same way for each trial subject

• Independent Variable– Rogooti for use on one group. Regular shampoo for

the other.

• Dependent Variable– After a specific length of time the hair would be

measured and the measurements would be compared to the beginning measurement. The same process would be used for those not using Rogooti.

Measurement of Results

•Why do you think units are important when measuring distance, volume, or mass?

•Think of as many units of measurement you can.

Two Systems of Measurement

• English– Inches, feet, miles, pounds, ounces

• Metric (SI or International System)– Meter, liter, gram

Which seems easier?• English

– 1 foot = 12 inches– 1 yard = 3 feet– 1 mile = 5280 feet

• Metric– 1 centimeter = 10 millimeters– 1 meter = 100 centimeters– 1 kilometer = 1000 meters

• In science, which do you think is more commonly used and why?