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!

Amusement park physics Have you ever wondered why it feels like you’re being lifted out of your seat as you start to go down a big hill on a roller coaster? Have you ever wanted to predict which way bumper cars will move after colliding? ENGAGE: Newton’s first law answers the first question. As the roller coaster ascends the hill, the rider’s body moves upward too. Due to inertia, the rider’s body tends to continue moving upward. When the roller coaster cars begin their descent, the rider’s body continues its upward motion until the seat belt restraints force the rider’s body to change its direction of motion. Bumper cars are an excellent place to observe Newton’s three laws in action. For a detailed guide to amusement park physics for middle school students, do an internet keyword search on “Amusement Park Physics with a NASA twist.” Newton’s laws can help you unlock the secrets of amusement park physics. You will find the answers to these questions and more in the Newton’s Laws of Motion module.

Time to investigate! Complete the lesson investigation: Newton’s Second Law How do force and mass affect acceleration? EXPLORE: Lead the lesson investigation: Newton’s Second Law. Afterward, assign the student reading.

Newton’s law of inertia When the net force is zero, objects at rest stay at rest and objects in motion keep moving with the same speed and direction. A net force is required to speed up an object. The force of the club provides the net force that moves the golf ball. A net force is needed to slow down the golf ball, too. When the club is no longer acting on the ball, friction supplies the net force. EXPLAIN: The surprising fact for many students is that force is required to slow down an object. Without friction, the golf ball would continue rolling with the same speed and direction—forever! To reinforce this concept, you may wish to show part 1 of the Newton’s laws video. It is accessed from the multimedia lesson home page.

What is inertia? Newton’s first law is often called the “law of inertia” because inertia is the property of an object that resists motion. Inertia comes from mass. Objects with more mass have more inertia. If you apply the same force to a bowling ball and a golf ball, which accelerates faster? The golf ball accelerates faster. The bowling ball’s mass is 100 times the golf ball’s mass. The bowling ball is more resistant to changes in motion. EXPLAIN: Asks students to describe events in which they have experienced Newton’s first law. For example, they may have noticed that it takes a lot more force to pull a wheeled picnic cooler full of ice and soda than an empty cooler.

Application: Seat Belts Why are seat belts important? Imagine you’re riding unbelted in a car going 55 km/h (35 mph). If the car crashes, your body will continue to move forward at 55 km/h until acted on by a net force. The car’s interior provides the stopping force. Your body collides with the dashboard, or possibly the windshield, at 55 km/h. A seat belt provides the net force that stops you before you collide with the car’s interior. EXPLAIN: Some students may think that it is not important to wear seat belts unless they are traveling at highway speeds (>100 km/h). You may wish to point out to them that 55 km/h (35 mph) is approximately the speed they would be moving when they hit the ground after falling off a 4-story building. Ask them if they would rather be strapped into a padded steel cage or just hurtling through the air unprotected in a fall like that.

Newton’s law of force and acceleration The acceleration caused by a force is proportional to force and inversely proportional to mass. EXPLAIN: Walk the students through a few sample scenarios. For example, if you double the force on an object, what happens to acceleration (assuming mass stays the same)? (acceleration doubles) If you double the mass, and keep force constant, what happens to acceleration? (acceleration is halved) To reinforce this concept, you may wish to show part 2 of the Newton’s laws video. It is accessed from the multimedia lesson home page.

Application: bumper cars Bumper cars are powered by electric motors. You can assume that all of the bumper cars in an arena have similar motors that produce about the same amount of force. A car driven by a seven-year-old girl bumps into the arena wall. Another car, driven by her dad, bumps into the same wall at the same speed. Which car experiences the greater backward acceleration? Why? EXPLAIN: Assuming that the cars hit the wall with the same amount of force, the car with the smaller total mass will experience the greater acceleration.

Newton’s law of action-reaction Every action force creates a reaction force that is equal in strength and opposite in direction. Think about the skateboard: You push on the ground. The reaction force is the ground pushing on you! EXPLAIN: The concept of reaction forces can be a difficult one for students. They may ask how an inanimate object (like the ground) can push on the skateboarder’s foot. The answer is that the force exerted by the ground is very similar to the force exerted by a spring. When the foot pushes on the ground, it squeezes the ground’s atoms together by a tiny amount. The atoms resist this squeezing. The ground’s atoms act like a bunch of very stiff springs. You don’t see the ground compress because the amount of compression is very small. The reaction force propels you forward.

Working with action-reaction pairs Both action and reaction forces are always there whenever any force appears. They always have the same strength. They always act in opposite directions. They always act on different objects. Both are real forces and can cause changes in motion. EXPLAIN: Ask your students, “If the action and reaction forces are equal in strength and opposite in direction, why don’t they cancel each other out?” The answer is that forces acting on the same object cancel each other out, but NOT forces acting on different objects. The illustration above shows the action force on the ball, while the reaction force acts on the hand. To reinforce this concept, you may wish to show part 3 of the Newton’s laws video. It is accessed from the multimedia lesson home page.

Application: rocket launches What happens when you blow up and then release a party balloon? It darts around the room! The action is the air moving out. The reaction is the balloon’s movement in the opposite direction. A rocket works on the same principle. The engine forces material out of the nozzle in one direction, causing the rocket to move in the opposite direction. EXPLAIN: To break free from Earth’s gravity, a rocket must reach a speed of over 40,250 km/h. This high speed requires a rocket engine to achieve the greatest possible action force, or thrust, in the shortest time. The engine must burn a large mass of fuel and push the gas out as fast as possible. The speed of the exhaust is often more than 1,000 m/s!

Time for Practice! Complete the lesson practice activity: Applying Newton’s Laws of Motion ELABORATE: Students can access the practice skills worksheet through the multimedia lesson home page.

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.