Lesson 3 of 9
Objective: Students will be able to explain how to set up an experiment, including the use of variables, by taking notes, performing an experiment, and analyzing the experiment's results.
The goal of this lesson is for students to understand that scientific knowledge is gathered through the use of experimentation. Furthermore, they will understand that when designing and carrying out experiments there are a number of things to keep in mind. This lesson is part of Science and Engineering Practice #3 -- Planning and Carrying out Investigations because students will learn (or be reminded of) the steps we take in experimentation, how to identify variables, and the various results of experimentation.
Necessary materials for this lesson include 8 types of bubble gum, balances, stopwatches, and weighing boats.
All of my students come into my classroom with some background knowledge of the scientific method and how to perform experiments, but many are confused on the types of variables (Independent vs. Dependent vs. Controls); the difference between hypothesis, theory, and law; and the way in which the scientific method is used by scientists. As I teach this lesson my goal is to elicit what students already think about these ideas, and then give them my definitions to use in class.
For example, students often think of a hypothesis as something that is proven correct or incorrect, but rather a hypothesis can support or negate a hypothesis (not 100% proven correct). Also, a hypothesis is not just an educated guess or prediction like some students often say, but rather it is a tentative explanation of what may happen.
Additionally, students should understand the difference between Theory and Law and that one does not come from another. They should see that a theory is based on a solid body of evidence that has been tested and supported with evidence numerous times. This is different from a law which is a generalization derived from facts, often without an explanation.
At the start of the lesson I ask students to read and reflect on the scenario "Doing Science" adapted from NSTA's Uncovering Students Ideas in Science book. The prompt is found as part of the beginning of the lesson PowerPoint and notes graphic organizer. I give students about 5 minutes to read and write down their answer to the prompt. I encourage them to work on this by themselves, and that we will have an opportunity to discuss later as a class.
After 5 minutes I take a quick hand-count of students who think that each response is the best answer. For example "Raise your hand if you think that Antoine has the best rationale for why scientists do science" etc. I will elicit student thinking of why they agree with a specific statement by calling on one of the students who raises their hand for each option.
I then go over the prompt with them and explain that all of the opinions have some good reasoning but that in my opinion the best answer is Marcos's, "I think that scientists use different methods depending on their question." I explain how although science often uses experimentation and that the scientific method is a nice way to perform experiments that not all scientists use the same steps or experiments. The goal of this activity is to get at students prior knowledge of what it means to do science, and to stress the fact that science is more than just just following the scientific method.
In this section students take notes as a PowerPoint is presented. I have them take notes on a note-outline graphic organizer paper (see student notes reflection). Before I go over each of the various definitions in the lesson I elicit student ideas of the concepts, and after each definition I give some examples.
For example when talking about what a "theory" is I elicit ideas about theories where students often say Big Bang Theory or the theory of evolution. During discussion I add in the Kinetic Molecular Theory as a chemistry example
When I ask students what they know about scientific laws, students come up with The Law of Gravity, and as we discuss laws if they have not already been addressed I mention Newton's Laws of Motion and Boyle's Law.
I continue in this manner asking students for their thoughts and relevant examples for each of the definitions on the Powerpoint and the graphic organizer.
Also, as I go over the notes I point out the important vocab words on the word-wall which is especially important for my English Language Learner students (see Word Wall reflection)
In this part of the lesson I give students an opportunity to practice the scientific method while doing a lab. The goal is for them to work through the scientific method (problem, hypothesis, material, procedure, analysis, and conclusion) while also practicing their lab skills (weighing), math skills (percentage and averages), and graphing skills.
I find it helpful to lead students through the lab by having them come up with the problem after reading the introduction, and then give them a sentence starter to help with the hypothesis. The sentence starter that I use is "Based on my previous experience the type of gum that will lose the greatest percentage of mass is _________ while the type that will lose the least is ___________.".
Once I give students the list of materials I go over the lab procedures. This year I simply had students follow procedure as outlined in the lab, but previous years I have left the procedure section blank and helped lead students through coming up with the necessary procedures (see Reflection for more details).
While I have students perform the lab I find it very important to walk around the classroom to ensure that they are working together and are on task. Furthermore, as students are doing the data analysis I check their answers to ensure that each group is coming up with a proper percentage mass lost. After students find their individual group's percentage mass lost I have them record on the class graph so that all students can copy onto their labs. This is an example of one class graph.
As students are completing the analysis part of the lab and writing/copying the percentage for each type of gum on their individual graphs, I tell them to begin to think about the conclusion questions, but that we will discuss as a group.
As most students are completing their graphs I announce "If you still need to finish copying the class graph you will have time in a minute, but lets all pause what we are working on to discuss the conclusion together." For this discussion I take volunteers through hand-raising, and if students do not raise their hands then I call on the class by group table for responses.
I start by asking students which gum lost the highest percentage of mass and which lost the lowest percentage of mass to make sure that everyone sees how to read the graph correctly.
I then ask them what they think was lost while chewing. I usually get the answer of "sugar" but I then point out to them that most of the gum is sugar free. I will pass out the packages of gum to the groups if I have already collected them and ask for a few volunteers to read off the ingredient of the gum to help elicit ideas about what was lost.
I ask students to think about sources of error, or ways that they could get different results than others doing the lab. I give a few moments of wait time and then ask for some suggestions. One way to keep track of suggestions is to make a table like this one where students see how for each error they can come up with a how that would affect results and how to change for next time.
One suggestion that I get is that there are different masses of the gum, but I explain that this shouldn't be an error because we are looking at the change in mass which doe not depend on the starting masses of the different types of gum. Other sources of error include using the balance correctly which could affect results by giving incorrect masses leading to incorrect percentage mass lost, the precision of the balance which could make it harder to differentiate between different types of gum, how fast students chew which could cause some groups to find that their gum lost more or less mass than others simply because of the way students chewed rather than the gum, and amount of saliva in students mouths which could cause some groups to find that their gum lost more or less mass than others simply because of how it dissolved in certain mouths rather than the gum itself.
In ways to counteract the error I get varied responses from use a more precise balance, double check that balance is zeroed before gum is weighed, have all students chew at same rate, and have each group chew all of the different types.
Because this is the first conclusion I have students write I use a sentence starter to encourage them to answer the questions completely and in full sentences. This is the sentence starter I use by writing on a paper and putting under the document camera:
"Based on the graph ___________ lost the least percentage of mass and therefore would last the longest, this (supports or negates) my hypothesis. Based on the graph ____________ lost the most percentage of mass and therefore would last the shortest, this _____________ my hypothesis. The ingredients that were lost while chewing were _________________. One possible source of error in the lab would be ____________________ which would effect my results by _____________________. If doing this lab again I would do ___________________ to counteract this error."
This is an example of a student lab (see reflection on grading labs for more details).
When students are done with the lab I have them turn in and grade using a rubric
To check for understanding I have students answer the practice questions at the end of the notes. When students complete the questions I stamp their papers for completion (which I check at the end of the unit when I do binder checks- see unit 1 lesson 8 for more details on binder checks). If there is not enough time to finish during class I have them take them home and when they come to class the next day I stamp their papers first thing.
When students have sufficient time to finish the questions, or the next day, I go over the answers. I do this on the overhead with a blank paper where I go from group to group having students answer the questions, or if there is less time then I just put up the answer key for the first few questions and elicit answers for their experimental design for just the last question
I also encourage students to make flashcards and quiz each other on the definitions at the end of this lesson if time permits. If we run out of time in this lesson than I have them do this another day in the unit where we have extra time. Sometimes I will prepare vocabulary flash cards for students and leave in the middle of each table. I have attached pictures of the ones I used for Unit 1 including the back and front.