The Why Behind Teaching This:
This unit covers standard 5-PS2-1: Support an argument that the gravitational force exerted by Earth on objects is directed down. During the unit, students will investigate a variety of objects to see that the force of gravity is constant on Earth and pulls things down towards its center. We will also be investigating a variety of ways to overcome gravity.
Several of the lessons in this unit are engineering design projects requiring students to follow the steps of the engineering design process to construct a project. These projects address standard 3-5-ETS1-1: Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost. It also addresses engineering standard 3-5-ETS1-2: Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem. There are also several experiments in the unit which address standard 3-5-ETS1-3: Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved.
This specific lesson addresses standard 5-PS2-1 by having students relate the downward motion of an egg to the pull of gravity. It also includes a review of how other forces, such as buoyancy, work against the pull of gravity.
The goal of this lesson is for students to identify the various forces acting on an object.
Students will demonstrate success on this goal by correctly labeling the forces and explaining how they affect motion on the diagram page.
Preparing for Lesson:
Wow the Students With a Demonstration
I have three cups of water set up on the table. I have a tray on top of the three cups with paper towel rolls on top of the tray placed directly above the cups. On top of each paper towel roll is a raw egg. I ask the students how I could get the eggs into the cups below. They tell me to hit the tray. I ask them if they believe the eggs will break when they go into the cup. They think the eggs will break. As you can see in the video of egg drop demonstration, I hit the tray causing it to fly out from under the paper towel rolls, and the eggs drop into the cups. I remove each egg and show the class that none of them broke.
Students immediately want a turn at trying this. They will get a turn, but not until we discuss how this all works.
Why Begin the Lesson With This Demonstration
This activity is one of my students favorites. They love having the opportunity to see who can get the egg in without it breaking. When they are really excited about something, they will remember not only the activity but the lesson behind it. This activity reviews every aspect of force and motion that has been discussed throughout the lesson. We discuss each item below throughout the lesson.
Explaining the Forces Acting on the Egg
I remove two of the cups so that there is now only one cup of water. I place the tray on top of the cup with a paper towel roll on the tray directly above the cup. I place the egg on top of the paper towel roll.
I ask students to explain why the egg is not moving. I give them time to discuss this with their group and write an explanation on a whiteboard. Group responses include things such as "the paper towel roll is holding it up," and "the paper towel roll is stopping it from going into the cup".
There was also a couple of groups that put it is not moving because there are no forces acting on it. I was able to use this time to clarify that there are always forces acting on objects. The forces are either balanced or unbalanced. This is a major concept that students need to understand so I was actually glad to see this on a couple of boards so I could review.
I am trying to get them to make the connection between what we have learned in class about forces, and what is happening in the demonstration. I ask them if the forces acting on the egg are balanced or balanced. They tell me balanced because the egg is not moving. We discuss the two balanced forces acting on it, gravity and an applied force from the paper towel roll.
Next, I ask students to discuss with their group what could make that egg move. I circulate while groups discuss this and record an explanation on a whiteboard. Most groups begin by just saying to hit the tray since that is what they saw me do. I asked them to come up with other ideas. They record things such as pull the tray, push the table, wind could move it.
I ask students to explain how forces act on it after the tray is knocked out from under it. I circulate to listen to conversations and guide the discussion as groups discuss it and record their explanation on the whiteboard. I had to lead groups to discuss the forces beyond gravity. Most groups recorded that gravity pulls the egg down into the cup, but did not extend past that. I ask them to explain what forces act on the egg after it falls into the cup, why doesn't the egg break?
All groups rewrote the explanation to include that gravity pulls the egg down into the cup, and buoyancy from the water pushes back up causing the egg to float.
Students Answer Questions for Chance at the Egg Drop
I allow students the opportunity to try and get the egg into the cup. Before they can have a chance to try, they must answer a question about how forces are acting on the egg. I place the questions for egg drop demonstration on the overhead, one at a time. I call on quiet students to answer the question. Almost every student in the class wants to try and get the egg in so only calling on quiet students helps control their excitement a little. It also helps because if students do not get the opportunity to try, it is usually due to their behavior. When a student answers the question correctly, they get the opportunity to apply a force to the tray and try to get the egg in the cup. Answers to the questions can be found at: questions for egg drop demonstration - answer key
If something unusual happens, such as the egg hitting the edge of the cup, or the egg falling onto the table, I will ask questions not on the question list. I may ask "What caused the egg to break?" The force applied by the cup or table. Any questions relating to the force and motion of the egg would be appropriate.
My students love getting an attempt at the egg drop. It is not as easy as it looks so sometimes it takes several misses before a student makes it. As you can see in the video of failed egg drop attempt that sometimes the egg misses the cup and lands on the table. This video of another failed egg drop attempt shows how sometimes it makes it in the cup but hits the edge on the way in and breaks. Finally a student will make it as you can see in the video of successful egg drop by student and the class gets so excited.
Why Have Them Answer Questions
I have students answer questions before attempting the egg drop for several reasons. One reason I have them answer questions is so I can see that they can make the connection between what has been covered in class, to a real situation. Another reason is to keep the activity focused on the forces involved and not on getting the egg in the cup.
Explaining The Egg Drop Through a Model
Throughout the lesson students have had the opportunity to discuss how forces are acting on the egg throughout the egg drop with their group, hear other students answer questions about the forces, and listen to my explanations and clarifications. After all of this practice, it is time for me to assess their understanding independently.
I provide each student with a copy of the egg drop diagram. The diagram requires them to identify the forces acting on the egg, and to explain how all of the forces involved change the motion of the egg. This diagram allows me to check understanding for each student independently. I am able to assess if each student understands and can explain that there are multiple forces acting on a single object, and that those forces change the motion of the object.
The majority of students performed very well on the exit ticket diagram. The biggest issue was that about half of the class wrote the word push or pull on the lines in the diagram instead of writing what is applying the push or pull. The directions say to "label each force and circle whether it is a pushing force or pulling force" but many students did not follow these directions. I will stress this to students in the future.