Why Does my Shadow Change? Day 3
Lesson 7 of 9
Objective: SWBAT apply what they learned from their models to the real world.
The Why Behind Teaching This
Unit 6 teaches students about Earth's Place in the Universe. Standard 5-ESS1-1: Support an argument that differences in the apparent brightness of the sun compared to other stars is due to their relative distance from Earth, is one standard covered. Standard 5-ESS1-2: Represent data in graphical displays to reveal patterns of daily changes in length and direction of shadows, day and night, and the seasonal appearance of some stars in the night sky, is the other standard covered.
Throughout this unit, students will learn about classifying stars, patterns of stars, and the effects of rotation and revolution. We will be creating models, graphing data, tracing our shadows, and much more.
This specific lesson covers standard 5-ESS1-2 by having students measure and record the length of their shadow at various times of they day. After measuring the length of their shadow, they create a graph to illustrate how their shadow changes throughout the day.
The goal of this lesson is for students to create a graphical illustration of how the length of their shadow changes throughout the day.
Students will demonstrate success on this lesson goal by accurately graphing the data collected in their investigation and identifying similarities and differences between their model and real life.
Preparing For The Lesson:
- A flashlight for students to use to make shadow puppets
I will be going over the steps for the investigation so no materials are needed
- A copy of the Real World Shadow Investigation Sheet for each pair of students
- A piece of sidewalk chalk for each pair
- A measuring tape for each student
- Large area outside for groups to spread out to complete the investigation
- A copy of the Graphing Changes in Shadow Length for each pair
The students have really enjoyed beginning the past couple of lessons with shadow puppets. Since I still have many students that have not had an opportunity to come up and make one, I continue with this warm up for this lesson. I call up students who have not yet had a chance to try making a shadow puppet, then move on to those who want to try another animal. I take this time to review what they have learned during their investigations.
The first student to come up makes a dog. The students correctly identify it as a dog.
To review the previous lessons, I ask the class what they think would happen to the shadow if I move the flashlight from straight on, over to one side. They tell me that the shadow will stretch out towards the opposite side. We move the flashlight to see if their prediction is accurate. I then ask what will happen to the shadow if I move the flashlight closer or further away. They tell me the shadow will get smaller if I move it closer and larger if I move it farther away. We move the flashlight to determine if they are correct.
Why Use Shadow Puppets
I have used this strategy to introduce the two previous lessons because the students enjoy having an opportunity to make the puppets and have the rest of the class guess what they are. I am able to ask some guiding questions and test out student predictions very quickly while students are having fun. By introducing the lessons in this way I am able to provide students some knowledge and experiences to refer back to when completing the investigation.
Setting Up the Life Size Comparison for the Model
Today students will be measuring their actual shadows outside to determine if their models were accurate. They will be going outside today at 8:30, 10:30, 12:00, and 1:30. Around 8:10, I give directions to students before taking them outside. You will need to take a measuring tape and a piece of sidewalk chalk outside with you.
Once you get outside, you will place an X in the middle of one of the sidewalk squares. After placing an X in the center, label each side of the square with the direction, (East, South, West, North). You will need to determine which of you will stand in the model, and which of you will be using the chalk to mark the shadows. Both of you will work together to measure.
I pass out a piece of chalk, a measuring tape, and a copy of the Real World Shadow Investigation Sheet on a clipboard to each group. We go outside and I go over the steps again, but this time model what each step looks like. I call a student over, I mark an X in the center of a sidewalk square and have her stand on it facing East. I mark where the tip of her head in the shadow is and then we act like we are measuring. Even though I explained the steps before coming outside, I go over them again so I am sure the steps are clear and students understand. Some students are visual learners so just telling them won't be effective with these students.
Completing the Investigation
Students spread out around the courtyard so that their shadows do not cross. They mark an X in the center of a square and label the sides North, East, South, and West. They record the direction of their shadow and measure the length when facing East, South, West, and North. They add the information to their investigation sheet. The purpose in having them do it from all four directions is to reinforce the fact that the direction of the shadow has nothing to do with the direction you are standing, but instead depends on the position of the sun. This is a common misconception that I want to make sure students understand.
You can see in the video of group measuring the shadow in the morning that the shadow is very long which is similar to what was observed when using the model. You can also see that it is stretching out at an angle, not straight back. This was something that was different from what was observed when using the model. One group mentioned this observation and we discussed what may cause this. Students concluded that it was due to the angle of the Earth at this time of year.
We leave the X on the sidewalk and I have them write their initials in the square they use. We will return to this location throughout the day.
At 10:30 we head outside to collect data for the second time. As we go out I ask students to make predictions on what direction their shadow will be stretching and if it will be longer or shorter than it was at 8:30. Students should have an idea of what to expect from their observations using their model in lessons 1 and 2. Students tell me that they think the shadows will still be going west, and that they will be shorter because the sun is more overhead than it was at 8:30.
Groups take out their investigation sheets and the same person that stood on the X the first time goes back to the X this time. They begin facing East and their partner marks where the top of their head ends in their shadow. After they measure, the person rotates to stand facing South. This continues for West and North. Groups notice that the shadows are now shorter and are still facing west so their predictions were accurate.
At 12:00 we head back outside. Once again, I have students make predictions on our way out. This time the students predict their shadow will be very small, but there is some debate as to what direction the shadows will be stretching. This is due to the fact that some groups got different results when using their model in day 2 of this lesson. Once outside, the same person returns to the X and each group records their observations. You can see in the video of group measuring the shadow at noon that the shadow is now very small and all groups found that the shadows still stretched west. We discussed how everyone was standing straight up, unlike the models, and that the sun was the exact same distance and not being moved around which did affect some groups with their model.
At 1:30 we went back outside to measure again. The shadows now stretched East, but were very tiny. If we did not dismiss at 2:00, I would have pushed this measurement back another hour just so students could see the shadows start to get longer again.
After the final measurement, students compare the data they got in the real life model, to that of the data from the cardboard model they made. They determine how accurate the mini-model was and we share. Overall, all groups felt that the mini-model was accurate. They are able to share two differences they noticed between the model and real life shadows. One difference was that the shadows stretched out at an angle, not straight back. I was very impressed to listen to the conversation that took place when trying to explain why this may be. One student said the angle the sunlight is coming in is different than the way the flashlight was coming in. Another student added that the light from the sun has to travel through space and our atmosphere which could bend it. Another student said that the Earth is tilted on it's axis which is what probably causes it.
Another difference that students noted was that the shadow got shorter between 12:00 and 1:30 but in the model, the shadow got longer between points 3 (12:00) and 4 (2:00). Students had another great science conversation about this which led to us all wondering if this was due to the fact that the days are longer at this time of year. Students asked if this would be different if we were to do this in the winter instead of the summer. When lessons lead to great conversations and more questions being developed by students, you know they learned from the activity.
Graphing Changes in Shadow Length
I provide each group with a copy of the Graphing Changes in Shadow Length exit ticket. Each group of students uses the data they collected to create a line graph to illustrate how the length of their shadow changes throughout the day. Because I taught this lesson towards the end of the year, I have begun introducing mean, which is a sixth grade math standard. Groups took 4 measurements at each time because they did one measurement from each direction. Instead of having students graph all of these measurements, I allowed them to use a calculator and find the mean at each time and just graph that one measurement. This provides them with the opportunity to practice going through the steps for finding mean (add and then divide the sum by the number of items you added together), but by using a calculator it eliminates errors in division with decimals.
We have previously made line graphs so students already know how to do this. They also have information in their notebooks to refer back to if they need help. After guiding them through finding the mean, they begin working on graphing the data and answering the questions at the bottom of the exit ticket.
All groups did well graphing. I thought it was interesting to see in the graphs how much of a change their was in the length of the shadows from 8:30 to 10:30, and little change there was after that. This is something that is more difficult to really see when written out as data in a chart.
In the written responses at the bottom of the exit ticket, I noticed that many groups felt that the models were only slightly accurate. Several groups noted that there were certain aspects that the model could not be true to, such as changes with the seasons. There was also a misconception that I came across on a couple of sheets. The way groups worded their answer to the second question sometimes seemed like they believe the sun is moving across the sky. I reviewed this by asking why the sun appears to move across the sky. When asked, all students could tell me that the Earth is rotating. I want to make sure they do not confuse the position of the sun, with the sun moving.