Why Does my Shadow Change? Day 2
Lesson 6 of 9
Objective: SWBAT use the model they created to investigate how the position of the sun affects their shadow.
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 investigate how a shadow changes as the position of the sun in the sky changes and the distance between the sun and Earth changes. Students built a model in the day 1 lesson and will use that model in this lesson to investigate and record changes in the shadow. They will then verify if the observations they recorded with their model are accurate by testing it outside in real life.
The goal of this lesson is to determine how the position of the sun and distance between the sun and Earth affect a shadow.
Students will demonstrate success on this goal by accurately completing the investigation and recording observations.
Preparing For The Lesson:
- Flashlight for shadow puppets
- A copy of the Shadow Investigation Sheet that was given out in the day 1 lesson
- the model that was built in the day 1 lesson
- a flashlight for each group
Students will be sharing their observations with the class so no other materials are needed.
I used puppet shadows to introduce the lesson on day 1 and the students begged me to let them make more. I told them in yesterdays lesson I would choose a few people today and tomorrow to make them as well. I call on a boy to come up and make one while the rest of the class guesses what he is making. After they guess correctly, I ask them what they think will happen to the shadow if we move the light further away. They tell me the shadow will get smaller. We test this by moving the flashlight back. The shadow actually got larger, not smaller. I then ask them what would happen if we move the flashlight closer. They tell me that the shadow would get smaller. We test this and it does in fact get smaller.
I choose another boy to come up and make a new shadow puppet. The class guesses what he is making and then I ask some more questions. I ask what would happen to the shadow if we move the light over to the side. The students tell me that the shadow will not look like the animal anymore. We move the flashlight over to the side, keeping it the same distance away, and the shadow gets longer, stretching to the opposite side. You can still tell what the animal is, an alligator, but it looks longer. I ask them what will happen if we move it to the other side. Students tell me it will look the same as it does now, just stretching to the other side. We do this and see that their prediction was correct.
Why Continue With the Shadow Puppets
The students really enjoyed making shadow puppets the previous day and begged me to continue. Since making shadow puppets again still allows me to deepen their understanding of shadows, I do the activity again. I am not just doing the same thing over, I am building on it today. I use today to introduce how the movement of light affects the shadow. This is something that we will be investigating today with our models.
Reviewing For Success
Students use the model they created in the Day 1 Lesson to investigate how the position of the sun affects the shadow made. We did the first section of the lab sheet in the first lesson so that students could familiarize themselves with how the model works and how to complete the lab sheet. Before they begin today I just briefly review how to use the model. Each pair of students gets out their model, situates the person in the center facing any direction, and uses a flashlight to model the sun. I provide each group with their Shadow Investigation Sheet from yesterday and explain that the first investigation is to see how the position of the sun affects the shadow so the only thing that should be changing in this investigation is the position of the sun. I point out the diagram on the lab sheet and model how they change the position of the sun. The second investigation for today models how the distance from the sun affects the shadow. In this investigation the distance of the light will change as well as the position.
I review the set up and investigation procedures before beginning to help students be successful in completing the task. Even though students did one investigation in the previous lesson, I cannot assume they remember how to do it all. I take the first few minutes just to quickly go over it so they can work independently with few questions. I point out the diagram with arrows representing the light from the sun (flashlight) that is on the lab sheet for the next investigation and tell students they will use these same positions for both investigations today.
Investigating How the Position of the Sun Affects Shadows
After reviewing the investigations with the class, the students begin the first investigation for the day. You can see in the video of group testing how the position of the sun affects a shadow that the student holding the flashlight stands with it 150 cm away and the girls measure. He then moved the flashlight across the "sky" keeping it at 150 cm. You can observe how the shadow changes from being a long shadow, to a very tiny short shadow. This is the same observation that all groups were able to see. The flashlight continued to the next position which would now be coming from the west, which causes the shadow to extend from the opposite side of the person.
Investigation How the Distance of the Sun Affects Shadows
After completing the first investigation, students repeat the same steps, but this time they move the flashlight to 50 cm from the center and 100 cm from the center to determine how the length of the shadow changes as the distance changes. 150 cm is also listed on the investigation sheet to compare these two distances to, however groups have already recorded the information for this from the previous test, so to save time they just copy down that information.
The group in the picture below came up with a very creative idea to help them with all of the changing measurements. They taped the beginning of the measuring tape to the center of the model board, and the other end to the bottom of the model person. They then held the measuring tape so the model person was at 100 cm and moved it across the "sky". They could then easily move the model person down to 50 cm and move it across the sky. They used a second measuring tape to record the length of the shadow. This saved so much time with remeasuring. I shared this with all other groups to help them as well.
As groups completed this investigation they observed that the shadows got shorter when the light was closer to the object. It was more noticeable when the light was all the way to the east or west and less noticeable when the light was more overhead because the shadow was already pretty short.
Sharing Lab Findings
After all groups have completed the investigation we share our findings from today's activities. The main goal of the investigation, changing only the position of the sun, was for students to see that the shadow gets shorter as the sun gets more overhead, and that the shadow is always on the opposite side from where the light is coming from. All groups shared that they were able to observe these patterns even though the data they got wasn't exactly the same. For example, measurements differed as much as 12 cm for the same position and some groups found that at position 3, the shadow faced east and other found it faced west. I believe the difference in the lengths was the accuracy of the distance the flashlight was held. Some students moved the flashlight around a lot while others were very good about holding it perfectly still. The difference in the direction of the shadow at position 3 was due to the way their model leaned. I saw this first hand. Some models were well supported and standing straight up, others leaned back, and some leaned forward. When the light is overhead the shadow will be in whichever direction the model is leaning.
The purpose in having students do the second investigation, where the distance from the sun changes, was for them to understand that shadows change throughout the year. I wanted students to see that as the seasons change, their shadow will change too. All students observed that the shadows got shorter as the light got closer. Again, measurements were off a little but not a lot. The shadows from position three changed very little because they were so small to begin with. Some groups even found that the shadow did not change at all from this position.