# Conducting an Investigation

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Conducting an Investigation
Scientific Method Conducting an Investigation

Essential Question Why do we trust that scientists have correct explanations for how ‘things’ work?

Observations Scientists use observations during an investigation to gauge how the process is going but they also make many observations to design their investigations. How do we make observations? Are some observations more important than others? Activity: Candle Observations On a piece of paper, you will make as many observations as you can about the candles that I show you. You may organize your paper how ever you would like.

Steps in the Scientific Method
Observation Hypothesis Experiment Data Collection Conclusion Retest

A scientist notices something in their natural world

Experiment A procedure to test the hypothesis.

Experiment Variable – factor in the experiment that is being tested.

Experiment A good or “valid” experiment will only have ONE variable!

An experimenter changes one factor and observes or measures what happens.

The Control Variable The experimenter makes a special effort to keep other factors constant so that they will not affect the outcome. Those factors are called control variables

What is the purpose of a control?
Controls are NOT being tested Controls are used for COMPARISION

Other Variables The factor that is changed is known as the independent variable. The factor that is measured or observed is called the dependent variable.

Examples of Controls and Variables
For example, suppose you want to figure out the fastest route to walk home from school. You will try several different routes and time how long it takes you to get home by each one. Since you are only interested in finding a route that is fastest for you, you will do the walking yourself.

What are the variables in your experiment?
Varying the route is the independent variable The time it takes is the dependent variable Keeping the same walker throughout makes the walker a control variable

One more thing… it is best to make several trials with each independent variable.

Remember: To be a Valid Experiment:
Two groups are required – the control & experimental groups There should be only one variable

Hypothesis A suggested solution to the problem.. Must be testable
Sometimes written as If… Then… statements Predicts an outcome

Hypothesis An example of a hypothesis might be that the salamanders have curved tails due to a pollutant in the moist soil where they live.

Rules in Constructing a Hypothesis
Do not use I, me, my, they – no possessive pronouns. If possible needs to be in an independent – dependent variable format. (IF this happens, THEN this will happen.) It is a statement, not a question Example: If salt is added to fresh water, then the water will take longer to freeze.

The If statement explains how the manipulated variable is going to be changed.
The then statement explains how the responding variable is affected by changing the manipulated variable. If the mass of a paper helicopter is increased, the the time it takes to drop to the ground will decrease. If fertilizer is given to a plant, then the growth of the plant will increase If a ball is hit with a wooden bat, then the ball will travel farther than an aluminum bat.

What is Wrong Hypothesis 1: If plants are given fertilizer, then the height of the plant will change In hypothesis 1 the then statement is not specific enough Hypothesis 2: If a plant’s height increases, then it was because of the fertilizer In hypothesis 2 the dependent variable was talked about in the if statement and the independent variable was talked about in the the statement. Hypothesis 3: If the height of the plant that is given fertilizer increases, then it is because the fertilizer gave the plant added nutrients. Hypothesis 3 has two problems. The first problem is like hypothesis 2, the if and then statements are mixed up. The second problem is this hypothesis does not give a prediction for the scientific question stated above. It gives a prediction on why fertilizers make plants grow more.

Practice 1 Amy wants to see how the amount of water in a pot affects the time that it takes for water to reach boiling point. She boils 100, 200, 300 ml of water. The time it takes for the water to reach boiling point increases as the amount of water increases. List the independent variable, dependent variable, and the needed controls Construct a possible Hypothesis

Answer to Practice 1 Independent: Amount of Water
Dependent: Boiling Time Controls: Type of water, heating apparatus Constructing a Hypothesis: If water amounts increase, then the time needed for water to reach the boiling point will also increase.

Practice 2 A study was done to see if leaves added to soil had an effect on tomato production. Tomato plants were grown in four large tubs. Each tub had the same kind and amount of soil. The 1st tub had 15 kg of rotted leaves mixed in the soil and 2nd had 10 kg. The 3rd tub had 5 kg and 4th tub had no leaves added. Each tub was kept in the sun and watered the same amount. The number of kilograms of tomatoes produced in each tub were recorded What is the independent variable? Dependent variable? What are the controls? Write a possible hypothesis for this experiment.

Answers to Practice 2 Independent: Amount of Leaves
Dependent: Kilograms of tomatoes produced Controls: Soil type and amount, Sun and water amount. Hypothesis: The larger amount of leaves added to soil will produce larger amounts of tomatoes. It is hypothesized that changing the amount of decomposing leaves in soil will not effect tomato growth.

Practice 3 James wondered if music had an effect on plant growth. He set up an experiment where 25 bean plants were placed in a chamber where music was played and 25 bean plants were placed in an identical chamber where music was not played. The growth chambers were kept at the same temp and all plants received the same amount of sunlight, fertilizer, and water. At the end of 2 weeks plant height was measured. What is the purpose? What is the independent variable? Dependent variable? Write a possible hypothesis for this experiment

Answers to Practice 3 Independent Variable: Music being played
Dependent Variable: Growth of plant Hypothesis: If music is played to plant over a period of time, then the growth of the plant will increase. If music is played to plant over a period of time, then the growth of the plant will decrease. If music is played to plant over a period of time, then the growth of the plant will have no effect

Data Results of the experiment May be quantitative or qualitative

Data Must be organized Can be organized into charts, tables, or graphs

Data – observations and measurements made during an investigation
Qualitative Data – describes the situation and reaction in descriptive terms. For example, qualitative involves the senses including sight, taste, hearing, touch, and smell. This would include color and shape Quantitative – includes those things that can be measured (length, time, mass, temp. etc.) Qualitative vs. Quantitative Data –

Do we need both? A well-designed investigation must have some type of MEASURABLE data, quantitative, but qualitative gives the measurable data more description and accuracy. Scientists use qualitative data to record observations that are difficult to measure or to give clarification to measured data.

Conclusion The answer to the hypothesis based on the data obtained from the experiment

Retest In order to verify the results, experiments must be retested.

Solving a Problem Identify a problem
State Observations about the problem Form a Hypothesis about the problem (if… then…) Design an Experiment to test the hypothesis Collect Data Form a Conclusion Retest

Let’s Review The Scientific Method

Scientific Method

A team of scientists wonder if the amount of Vitamin A given to laboratory white mice would affect the number of offspring born. An experiment is set up using the same species of white mice. Each mouse in the study gets the same amount of food, daily exercise, and is kept at the same temperature. Once group of mice gets extra vitamin A supplements added to their food. The number of offspring are counted and recorded. Which of the following is the best Hypothesis – Explain why the wrong ones are incorrect. Mice will have more offspring if they are given Vitamin A. If the mice are exposed to Vitamin A, then the amount of offspring will increase. If you give mice Vitamin A, then they will have more offspring I think the offspring number will increase if the mice are exposed to Vitamin A.

On Your Own A scientist wonders how acid might effect salamander’s hatching and growth. A scientist places 100 salamander eggs (Group X) in a pond that is exposed to acid rain. He places another 100 eggs (Group Y) in a pond where acid rain has not been detected. The conditions such as temperature, mineral content of the water, amount of sunlight are as similar as possible in both areas. Determine Independent Variable? (2pts each) What are some possible Dependent variables? Construct an Hypothesis for this experiment.

On Your Own Candy wondered if caffeine would affect the breathing rate of goldfish. She went to the store and purchased 10 goldfish of approximately the same age and size, identical containers, food, and caffeine tablets. In one container she placed 5 goldfish with no caffeine. In the other container she placed 5 goldfish with caffeine tablets dissolved in the water. She observed the goldfish behavior and counted the operculum (plate that covers gills) movements in both containers of fish. Determine Independent Variable? What are some possible Dependent variables? Construct an Hypothesis for this experiment.