Developing a Scientific Hypothesis

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  • 0:01 What Is a Hypothesis?
  • 1:04 Creating Your Hypothesis
  • 2:39 Thomas Edison's Hypotheses
  • 4:23 Poor Samples
  • 7:02 Lesson Summary
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Lesson Transcript
Instructor: Paul Brege

Paul has been teaching middle school science for the last 10 years, and has his bachelors degree in Elementary Education.

This video describes how to create a hypothesis and includes the three main things needed to create a strong hypothesis. You'll learn how to make a clear statement that can be both tested and measured.

What Is a Hypothesis?

Have you ever been reading a book where something was happening, but you couldn't quite figure it out? Possibly a spy novel, or a mystery, or perhaps even a book where you get to pick what the main character does next?

Maybe as you turn the pages in that thrilling 'who-done-it' mystery that you're reading, you start to get a feel for who the real villain might be. As you think back over everything you previously read, you're fairly confident that the butler was the real culprit the entire time; you have evidence that links him to the crime and an overall strong gut feeling about it. It must be the butler! You tell all your friends and make sure that they know that you were the one who said it first!

Books often give clues as to what might happen next. Sometimes you can even make a guess as to what is going to happen by the end of the story. Those guesses might be right, but sometimes they're wrong, too. When you make a guess in a book as to what might happen next, you're probably using clues from what's already happened to make that guess. In the science world, we call a guess like that a hypothesis.

Creating Your Hypothesis

Within the realm of classrooms, science fairs, and especially science experiments, scientists often need to make an educated guess called a hypothesis, which is a statement that says what scientists think will happen when an experiment is tested. When making your own hypotheses, scientists generally follow a few guidelines. The hypothesis is typically a clear statement and, most importantly, needs to be something that can both be tested by experimenting and can be measured.

Let's look at some examples. Pretend you want to perform an experiment with plants where you'd like to see which temperature of water will make plants grow the tallest. One hypothesis could be: room temperature water will make plants grow taller than boiling water. This would be an educated guess because you've only ever seen people water plants with water from a can or faucet, never boiling water, never a boiling pot. Go back to your checklist:

  1. Is this a clear statement? Yes, you think that room temperature water will make plants grow better than boiling water.
  2. Could you test it? Yeah, you could pour a set amount of room temperature water onto a potted plant once a day for a week. You would also need to have another plant getting the same type of boiling water each day.
  3. Could you measure this? Yes, you could measure the plants every day with a ruler, and after a week, see which one is taller.

This would be a great example of a good hypothesis because it can be both tested and measured. And don't forget, it's okay if your hypothesis is incorrect. Scientists discover things every day by learning what doesn't work. Let me tell you a story.

Thomas Edison's Hypotheses

Thomas Edison is known for many things, one of which is his work on the light bulb. While he didn't actually invent the light bulb, he did make it better! Originally, light bulbs only lasted a short time, but then Edison and his team started experimenting.

Edison and his team needed to create a new hypothesis every time he tried a new material in his light bulb. Carbonized cotton thread became the material of choice, but Edison wanted his bulbs to last even longer. So, the testing went on: he tried hundreds of things, thousands of things; he tried tree bark; another time, he tried wild grass; one time he tried horse hair, gold, even bamboo - every time he was putting a new item into the bulb he was coming up with a new hypothesis.

Would this type of hypothesis fit our original checklist? Let's see! Can it be tested by experimenting? Yes, as he put each of the items into the bulb and passed a current through them, the materials either gave off light or they didn't. Could those tests then be measured? Yeah, Edison and his team measured by timing how long the materials burned for.

Looking back at our original goal of creating a hypothesis, doesn't a hypothesis need to be correct for it to be valuable? What about being right? Well, Thomas Edison knew that it didn't matter if your hypothesis was correct or incorrect, and so should you. While working tirelessly on the light bulb, Thomas Edison and his team discovered a very long list of things which didn't work very well as light bulb filaments. Edison is even quoted as having said, 'I have not failed. I have found 10,000 ways that won't work.' If your hypothesis proves to be incorrect, don't worry - it happens all the time.

Poor Samples

Look over this next list of samples. These are all poor examples of hypotheses as they're written right now. Remember, a good hypothesis will state what will happen when it's tested:

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