Warm Up: What Do You Know About Balanced and Unbalanced Forces?
Have students complete the Think-Pair-Share activity in the Student Guide. Students should complete part 1 individually, and then work in pairs to answer question 2. Then, ask a student to come forward and draw two diagrams on the board: an object with balanced forces acting on it, and an object with unbalanced forces acting on it.
Review Newton’s First Law of Motion: An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
Explain that this law is often referred to as the "law of inertia," and review the definition of inertia: the resistance of an object to change its state of motion. Let students know that they will explore Newton’s First Law later in the lesson.
Have students play Motion Force with their partners for approximately 20 minutes. Students should continue where they left off with the previous game by selecting the appropriate mission.
Pause and Think
Have students pause the game after about 10 minutes and ask them to share how the experience is different from the first game play session. Ask the following questions related to Newton’s First Law of Motion:
- How did your success compare to the success of your first game? Why do you think this is so?Sample answer: I was more successful this time because I was more familiar with the forces needed to move the spacecraft along the trajectory. I was also more familiar with how to use the game tools like the launcher and the rocket boost.
- Did you learn anything through trial and error? Explain.Sample answer: Yes, sometimes I had to try different forces with different directions. If the mission failed, I could replay it and adjust the forces as needed.
Explain to students that you are going to demonstrate the concept of inertia. Ask how inertia relates to Motion Force. (Sample Answer: The spacecraft tend to resist changes in their current states of motion unless forces act upon them.)
Ask students if they can think of any real-life examples of inertia. Provide an example if needed:
Suppose you are standing on a bus that is not moving and you are not holding onto anything. Suddenly, the bus starts to move forward. What happens to you? Likely, you fall backward. You were originally at rest, so you tend to stay at rest. When the bus moves forward, your body tries to stay in the same position as before, so you appear to move backward.
Complete the demonstration as follows:
- Fill the glass about three-fourths with water and center the pie pan on top of the glass.
- Place the paper tube upright on the pie pan so it is directly above the water in the glass.
- Set the egg gently on top of the paper tube so it is sitting upright.
Hit the edge of the pie pan with a solid horizontal whack. Make sure you hit the pan horizontally, which should cause the pan and tube to fall sideways and the egg to fall into the glass of water.
- Note: There are videos online that shows how this demonstration is completed. Use the keyword search: Egg Drop Inertia Experiment.
Discuss how the demonstration shows inertia: the egg was at rest and tended to stay at rest, even when you hit the pie pan. Gravity caused the egg to fall into the glass.
Hands-On Activity: Using Forces to Move a Ball
Explain to students that they will be completing an activity that will help them observe forces in action. Have students read the instructions in the Student Guide, and then review the following points as a class:
- The object of the game is to use forces to get the ball into your opponent’s goal area.
- Straws cannot touch the ball.
- You must keep your hands behind your back.
- Do not touch the table.
- Blow gently and take your time. If you feel dizzy at any time, stop and tell your teacher.
Allow students to play the game for about 10 minutes. As they play, students should keep score and think about the way in which balanced and unbalanced forces play a role in the game. After playing, give students about 5 minutes to write down all of their observations on an 8 x 11 sheet of paper.
Have students share their observations with the class. The general take away of the activity is that, when the forces are equal on the ball and in opposite directions, the ball does not move. When the forces are unequal, the ball moves or changes direction.
Have students complete the Exit Slip activity in the Student Guide and submit the activity before leaving the classroom. Review the student responses before the next lesson.