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To the teacher: This CPO Science PowerPoint presentation is designed to guide you through the process of presenting the lesson to your students. The presentation uses a 5-E teaching model: Engage, Explore, Explain, Elaborate, and Evaluate. The PowerPoint Slide notes indicate where you may want to bring in various lesson elements such as quizzes, readings, investigations, animations, and practice materials. Additional science background information is provided in the slide notes where appropriate. You can view these notes by selecting “View,” then “Normal.” You will see the notes pane at the bottom of the PowerPoint workspace. Additionally, the slide notes are available as a separate document, accessible from the lesson home page. The slides that follow are intended for classroom use. About the slide notes: The slide notes for this presentation are available in a separate document that you can print and look at while you use the slides. You can access the slide notes document from your teacher lesson home page. Enjoy the lesson!

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**What causes the space shuttle’s acceleration?**

What produces the unbalanced force needed for liftoff? Does the mass of the space shuttle “system” (shuttle + rockets) change during the first few minutes of flight? Is the acceleration of the space shuttle system constant or does it change? ENGAGE: The unbalanced force is produced when hot gases are ejected from the rockets. The mass of the rockets decreases as the gases are ejected. This means that the mass of the space shuttle system decreases. Students will learn in this module that if the same force is applied to a smaller mass, acceleration increases. Therefore, the acceleration of the space shuttle system changes. The shuttle starts off moving slowly but accelerates faster as the mass decreases.

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**Time to investigate! Complete the lesson investigation:**

Force and Acceleration What unbalanced force is acting on the car? Is this force acting on the car during its entire trip along the ramp? Can you describe the speed of the car during its trip along the ramp? EXPLORE: Lead the lesson investigation: Force and Acceleration. Ask the students to keep in mind the three questions on the slide as they observe and gather data about the car’s movement along the ramp. After the investigation, assign the student reading.

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Newton’s Second Law Newton’s second law helps us understand the connection between force, mass, and motion. EXPLAIN: Remind students what they already know about acceleration—what it is, and how it is produced. Newton’s second law will help us see how changing the force and/or changing the mass of the object affects the acceleration. Acceleration is a change in the speed or direction of an object. Unbalanced forces produce acceleration.

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**What happens to acceleration if you change the force?**

If you double the force pushing on the 1-kilogram cart, how does the acceleration change? If you reduce the force by half, how does the acceleration change? What would happen if you tripled the force? Acceleration is proportional to force. EXPLAIN: Discuss the first two questions with the students. The answers are depicted in the illustration. Next, see if they can make predictions based on what they have learned from the illustration. Can they guess what happens when the force is tripled? What if the force is reduced to one-tenth of its original value? Explain that when one variable increases or decreases by the same factor as another variable, we say that the two variables are proportional.

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**What happens to acceleration if you change the mass of the object?**

If you double the mass of an object, and push with the same force, what happens to the acceleration? If you cut the mass of an object in half, and push with the same force, what happens to the acceleration? Acceleration is inversely proportional to mass. EXPLAIN: Ask the students to find the answers using the graphic as a guide. Then ask them to predict what would happen if they tripled the mass. They should be able to explain that if you increase the mass by a factor of x, the acceleration is divided by a factor of x. We call this an inversely proportional relationship.

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**Time for Practice! Complete the lesson practice activity:**

Newton’s Second Law Here is a sample problem to work out together as a class: An airplane needs to accelerate at 5 m/s2 to reach take-off speed before reaching the end of the runway. The mass of the airplane is 5,000 kg. How much force is needed from the engine? ELABORATE: Discuss the problem. You are asked for force (F), and given mass (m) and acceleration (a). Use Newton’s second law, F = ma, and plug in the numbers to find the answer. Remember that 1 newton = 1 kg.m/s2. So, Force = (5,000 kg) × 5 m/s2 = 25,000 kg.m/s2 = 25,000 N. Use the video accessed from the multimedia lesson home page to reinforce the concepts presented in this module.

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Show what you know! Try the lesson’s interactive quiz, or complete a quiz that your teacher can print out for you. Hint: You might want to review your lesson reading piece one more time before trying the quiz. EVALUATE: Print out the 10-question quiz for students to complete, or have students work individually at computers to complete the interactive quiz they can access from the multimedia lesson home page.

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