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 identifying the force of gravity and giving examples of how it affects motion. Other forces such as buoyancy, friction, air resistance, applied force, and magnetism are also introduced in this lesson. They will be referred back to later, during investigations and experiments, as ways to overcome the force of gravity. Introducing these other forces is important so students understand that gravity is not the only force acting on things. This helps them better understand how gravity works since not all things are moving down.
The goal of today's lesson is for students to be able to identify the six main forces and give examples of each.
Students will demonstrate success of the lesson goal by answering 100% of the exit ticket questions correct.
Preparing for Lesson:
What Makes Things Move
I place a tennis ball on a table in the front of the classroom. I ask students what could get that tennis ball to move. The responses I get are to push it, wind could blow it, and to shake the table. I demonstrate each one as it is identified. As I blow on the ball to model wind, I ask the class if blowing is a type of push, just air doing the pushing instead of my hand and they say it is. As I shake the table I ask if that is also a push, this time by the table, and they say it is. I ask if there is any other way to get the ball to move besides applying a push. After thinking about it for a while, a student tells me to pick it up which would cause it to move from the table to my hand. I do that and as I am picking it up, I ask if I am pushing the ball. Students tell me no, I am pulling it up. I place the ball back on the table and pull it forward with my hand to show another pull. I tie a piece of yarn around it and pull that to make it move by another pull.
I explain to students that all of these examples included pushes or pulls that caused things to move. These are all known as forces.
Why begin with demonstrations
I introduce forces in this way because, though students are aware of what causes things to move, they are not yet aware of the science vocabulary related to forces. By having them identify ways to make things move, and then me demonstrating them, it allows them to make the connection between what they already know about motion to the new vocabulary I am about to introduce.
Creating the Foldable
I pass out a precut copy of the forces foldable to each student. I also provide a copy of the force foldable definitions to those who need the modification. I have the definitions precut and in a Ziplock baggie for the students that receive them. This requires them to read the definitions as we go through them so they can correctly identify the one that fits. As students glue the foldable into their science notebooks, I glue a copy in my notebook and place it on the overhead. I do this mainly as a model for my ESE and ELL students, but this also helps struggling writers and those who are not good spellers. Under the top flaps that say "What are forcces?", I record: A PUSH or PULL that causes a change in motion.
I continue on by going through each type of force beginning with gravity. We are going to be investigating each of the forces through future lessons, today I am just introducing them. On the inside flap for gravity we record, A pulling force that pulls things DOWN towards the center of Earth. Students copy this into their notebooks and I circulate to check for accuracy. I ask for some examples of when they may see gravity at work. Students tell me things like: when a ball falls to the ground, when someone falls out of their seat, when you jump up and come back down, etc.
The next definition we write is under the applied force flap. We open it and record, A pushing or pulling force exerted by a person, object, air, or water that pushes or pulls on an object. I explain that an applied force is one that is being applied by something. I ask for examples of when they may have seen or used an applied force. They tell me things like: when we move our pencil, ride our bike, skateboard, when we throw a ball, etc.
Air resistance is the next definition in our foldable. Under that flap we record: A pushing force created by the particles in the air that acts against gravity. I tell students that this is actually a form of friction because by rubbing against the particles in the air, it slows the object down as it travels through the air. I ask for examples of when air resistance may occur. Students have the most difficulty with these examples but I do get a few, such as: when a paper airplane is thrown, when a parachute falls, and when a real plane raises the flaps on the wings.
The next flap on our foldable is friction. We define it as A pulling force that acts against motion to slow down or stop things from moving. I explain that some surfaces produce more friction then others. I ask them if it is easier to ride their bicycle on the sidewalk or through the grass. They tell me the sidewalk and I explain that is because there is more friction with the grass. I ask what other surfaces may have a lot of friction and they tell me sand and carpet. I ask them what surfaces may have little friction and they tell me tile and wood.
We record, An upward pushing force exerted by water as the definition for buoyancy. Students are able to identify two examples, they tell me boats floating and when fish die they float up to the surface. I tell them that they experience buoyancy every time they go swimming. I ask how many of them have ever floated on their back in the pool, tried to push a ball under the water just to have it pop back up, or lifted their mom or dad up in the pool. This all happens because water is pushing up and helps you float or pick someone heavy up in the water.
Our last definition is magnetic force. Before we record this definition I ask students if they think this is a pushing force or pulling force. The first answer I get is a pulling force. I ask what it pulls and students tell me metal objects and other magnets. I ask if it can ever push things. I can tell that some students are not aware that it can push other magnets with the same charge, while other students are nodding their head yes. I ask one of the students who says yes to explain. She tells me that sometimes two magnets push against each other. We record the definition in our foldable as, A pulling force when placed near magnetic objects and other magnets with opposite poles. A pushing force when next to a magnet with the same pole facing.
Observe the Forces In Station Rotations
I have students rotate through stations observing each of the forces at work. We will be spending more time on each individual force throughout the unit, these stations are set up to provide them with some background knowledge and experiences to refer back to during future lessons.
I provide each student with a Forces Rotation Lab Sheet to complete as they rotate through the stations. Providing them with a lab sheet ensures that they have a task to complete, observations to make, and questions to answer while completing each task. Without the guidance of the lab sheet, students would just be playing with the materials and not focusing on how the identified force is affecting motion.
I have the Force Station Signs hung up around the room and all materials needed, (as described on the lab sheet) at each station. I assign groups of 3, each group is made up of one ESE/ELL student, one regular student, and one high student. I am also careful about placing students who play around together. When stations are focused around manipulating objects, it leaves the door open for students to play around. I want to set my students up for success by placing them in groups they work well in.
I go through the expectations for the station rotation prior to sending groups to stations. No moving from the station you are assigned. No talking to other groups. No playing with materials, only the material being used should be in your hands. Clean up messes. All students should be actively involved and have all answers recorded.
I send groups out to a station to begin. I circulate to listen to conversations and to ensure all students are on task. I question groups as I rotate about how the force they are observing impacts the motion of the objects.
At this station, students are testing if gravity has the same effect on all objects. They will be testing 3 different size balls to see if they fall at the same rate. You can see in the video of kids dropping three balls that they do not fall at the same time. The baseball falls first and it is the heaviest. This gets them thinking about the impact that weight and size play on the motion caused by gravity. Students are also observing and comparing a regular balloon to one filled with helium. The balloon of air is pulled all the way to the ground, while the one with helium floats up.
This observation leads to a conversation about how and why this happens. The majority of students cannot explain this. Both of these activities build background knowledge that will help students make the connection between size or weight, gravity, and how that affects friction.
In this station, students are rolling a ball across tile, sand, and rocks and observing how the motion of the ball is different.
As you can see in the video of student rolling ball on various surfaces, the ball goes far on the tile and barely moves on the sand and even less on the pebbles. The purpose of this station is to get the students to relate the stopping of the ball to the force of friction and to understand that different surfaces produce different amounts of friction. We will be doing an experiment testing friction with different surfaces so this will help students make their hypothesis for that experiment later in the unit. Another activity at this station is for students to run the eraser end of a pencil on the table very quickly numerous times and then touch the eraser. This activity serves two purposes. One, is so students relate friction to rubbing because in essence it is created when two surfaces rub against each other. The other purpose is so students can observe that friction produces heat.
Students are comparing how buoyancy in water affects clay in this station. They begin with a ball of clay which will sink in water. They then flatten the clay out and see that it will float in water. The lab sheet asks them to explain what caused the change in motion. This activity helps students begin to make the connection between surface area and the impact the force has on it. When we start talking about net force, this activity will provide background knowledge on how the force of gravity is sometimes stronger than buoyancy and how sometimes, if the surface area is large enough, buoyancy is stronger than the force of gravity.
This station provides an opportunity for students to see how magnets can be both a pulling force and a pushing force. The Paperclip Maze is a fun way for students to experience magnets applying a pulling force on metals. As you can see in the video of the paperclip maze, one student held up the maze while the other students used a magnet to move the paperclip through the maze. After they complete this activity they try to put two magnets together to apply a pushing force. I provided two magnets with the North and South poles clearly marked, this helps students see when the same poles are together they push and when the opposite poles are together they pull. Students having the opportunity to see this first hand will help them remember it better then me just telling them.
Students observe how the surface area of an object affects the impact that air resistance has on it in this station. You can see a student dropping a ball of paper and another dropping a flat piece of paper in this air resistance video. The ball of paper fell straight down, while air pushing up against the flat piece caused it to fall much slower and sway side to side on its way down. We discuss how the surface area is greater on the flat piece of paper which will help them make the connection back to buoyancy which is also impacted by surface area.
In this station, students test the impact various items have on the motion of a ball. They should find that the air moving from the fan should move the ball, the ruler poking the ball should cause motion, and the water being poured on it should also cause it to move. Students will observe that the applied force has to be strong enough to move it by observing that the moving air from a piece of paper (less strong then the fan) does not move the ball. They will also observe that the force has to touch the object in order to move it, by drinking the water instead of pouring it on the ball, it will not cause motion.
Wrap Up Discussion:
Students spend about 20 minutes in stations, about 3 minutes per station. After all stations are completed, they return to their seats for a class discussion to share their observations. We go over the lab sheet so students can share what they observed and how or why the force impacted the motion of the object. This discussion allows for students to hear things they may not have observed in the station and to possibly get another view on why it happened.
Bringing the class back together and discussing the observations is important to me as the teacher because it allows me to help students make some of the connections between forces. For example, the impact of surface area on buoyancy, as well as air resistance, may not be something they realized when doing each in isolation of each other. By reflecting back on what they observed, I can guide them to these connections.
After our discussion about observations that were made in the stations, I provide each student with a copy of the types of forces exit ticket. They complete the exit ticket independently. The main focus of the exit ticket it to determine if they can define a force, and identify some of the forces discussed today.
The majority of students performed very well on the exit ticket. I had 6 students out of 38 that missed one or more. 4 out of the 6 that made errors missed the first one because they recorded an example of a specific force (such as the 2nd picture above), instead of writing what all forces do, push or pull. This was something easy to reasses. I called these 4 students up to my desk as I was grading them and told them I did not want a specific example, I wanted to know what all forces do. Only 1 out of the 4 could tell me they all push or pull. The other 2 students missed several, they are both 2 of my very low ESE students. These two students will need more examples and a lot of focus during instruction throughout the unit.