Measurement Corner #16: Strong hypotheses Consider the following hypotheses. Hypothesis #1: If air resistance is negligible, any two objects falling under the influence of gravity will fall equal distances in equal amounts of time. Hypothesis #2: If air resistance is negligible, a rock and a hammer will fall under the influence of gravity equal distances in equal amounts of time. Hypothesis #1 is Galileo's hypothesis that we looked at in Measurement Corner #15. These hypotheses are both testable and falsifiable. They can both be tested by exactly the same experiment. 1. Do you think either of these hypotheses is better than the other, or are they equivalent? Hypothesis #2 only asserts that gravity affects these two specific objects the same, but hypothesis #1 predicts that all objects will fall in the same manner. Hypothesis #1 is more general than hypothesis #2. In science, we want to know general principles for how nature works. Therefore, general hypotheses are better than limited hypotheses because they are applicable to a broader scope of situations. A word of warning is in order here. Saying that a hypothesis should be general is not the same thing as saying it should be vague. Consider this hypothesis. Hypothesis #3: Any object that is influenced only by gravity will fall. 2. Do you think that hypothesis #3 is better than, worse than, or equivalent to hypothesis #1? A major advantage of hypothesis #1 is that it is specific when it says "equal distances in equal amounts of time". Hypothesis #3 is general, testable, and falsifiable, but it is not very specific and therefore not very useful. The strongest hypotheses are both general (applicable to a wide variety of situations) and specific (making precise statements about the outcome of an experiment). With some practice, you can build strong hypotheses starting with weak hypotheses by adding generality and specificity. Example: A 4 year old boy has a ball made with two hemispheres of different density. He makes a game out of predicting which side of the ball will end on the bottom when he rolls the ball. In the first few tries, he might make a prediction such as "When I roll the ball this time, I think the green side will be down." After a while, he decides to make a more general hypothesis. "Every time I roll the ball, the green side will be down." Example: Your friend notices that when he holds an inflated balloon near a heater, the balloon expands slightly. He hypothesizes as follows. "When the temperature of the air inside a balloon increases, the air pressure inside the balloon increases so the balloon expands."This hypothesis can be made more precise by making it quantitative. "The volume of the balloon is proportional to the air pressure inside the balloon and proportional to the temperature of the air." Consider the following hypothesis. A 3" grader is working on a science fair project. He has noticed that the cooking instructions on a box of pasta say to boil the pasta in water with some salt dissolved in it. He proposes the following hypothesis. "Maybe dissolving salt in the water makes it easier to boil." 3. Reformulate this hypothesis within your group to make it as strong as possible. In other words, make it more general and more precise