Slide 4-1 Force Vectors 2015 Pearson Education, Inc. Slide 4-2 Combining Forces A net force that is the vector sum of all the forces: The net force is sometimes called the resultant force. 2015 Pearson Education, Inc. COMP: Symbols with overarrows are MathType Slide 4-3 QuickCheck 4.1 The net force on an object points to the left. Two of three forces are shown. Which is the missing third force? A.B. C. D. 2015 Pearson Education, Inc. Slide 4-4 QuickCheck 4.1 The net force on an object points to the left. Two of three forces are shown. Which is the missing third force? Vertical components cancel A.B. C. D. 2015 Pearson Education, Inc. Slide 4-5 Vector Addition Practice 1 John pushes a box with a force of 45 N and Mark pushes the same box with a force of 50 N in the same direction. Draw a vector addition sketch and calculate the net force. 2015 Pearson Education, Inc. Slide 4-6 Vector Addition Practice 2 John pushes a box with a force of 45 N and Mark pushes the same box with a force of 50 N in the opposite direction. Draw a vector addition sketch and calculate the net force. 2015 Pearson Education, Inc. Slide 4-7 Vector Addition Practice 3 Greg lifts a 6N bag of sugar using a force of 8N. Draw a vector addition sketch and calculate the net force. 2015 Pearson Education, Inc. Slide 4-8 Vector Addition Practice 4 Grace pulls a wagon with a force of 25 N. Calculate the x and y components of her pull. 2015 Pearson Education, Inc. Section 4.6 Free-Body Diagrams 2015 Pearson Education, Inc. Slide 4-10 FBD Practice Draw a FBD of a person standing in an elevator at rest Draw a FBD of a person standing in an elevator that is accelerating upward 2015 Pearson Education, Inc. Slide 4-11 FBD Practice Draw a FBD of a person in an elevator that is in freefall. 2015 Pearson Education, Inc. Slide 4-12 FBD Practice Lisa is pushing a block across the table at a steady speed. Draw a free-body diagram. 2015 Pearson Education, Inc. Section 4.7 Newtons Third Law 2015 Pearson Education, Inc. Slide 4-14 Newtons Third Law Motion often involves two or more objects interacting with each other. As the hammer hits the nail, the nail pushes back on the hammer. A bat and a ball, your foot and a soccer ball, and the earth-moon system are other examples of interacting objects. 2015 Pearson Education, Inc. Slide 4-15 Interacting Objects An interaction is the mutual influence of two objects on each other. The pair of forces shown in the figure is called an action/reaction pair. An action/reaction pair of forces exists as a pair, or not at all. 2015 Pearson Education, Inc. Slide 4-16 Reasoning with Newtons Third Law 2015 Pearson Education, Inc. Slide 4-17 Runners and Rockets In order for you to walk, the floor needs to have friction so that your foot sticks to the floor as you straighten your leg, moving your body forward. The friction that prevents slipping is static friction. The static friction has to point in the forward direction to prevent your foot from slipping. 2015 Pearson Education, Inc. Slide 4-18 Runners and Rockets The rocket pushes hot gases out the back, and this results in a forward force (thrust) on the rocket. 2015 Pearson Education, Inc. Slide 4-19 QuickCheck year-old Sarah stands on a skateboard. Her older brother Jack starts pushing her backward and she starts speeding up. The force of Jack on Sarah is A.Greater than the force of Sarah on Jack. B.Equal to the force of Sarah on Jack. C.Less than the force of Sarah on Jack. 2015 Pearson Education, Inc. Slide 4-20 QuickCheck year-old Sarah stands on a skateboard. Her older brother Jack starts pushing her backward and she starts speeding up. The force of Jack on Sarah is A.Greater than the force of Sarah on Jack. B.Equal to the force of Sarah on Jack. C.Less than the force of Sarah on Jack. 2015 Pearson Education, Inc. Slide 4-21 QuickCheck 4.17 A mosquito runs head-on into a truck. Splat! Which is true during the collision? A.The mosquito exerts more force on the truck than the truck exerts on the mosquito. B.The truck exerts more force on the mosquito than the mosquito exerts on the truck. C.The mosquito exerts the same force on the truck as the truck exerts on the mosquito. D.The truck exerts a force on the mosquito but the mosquito does not exert a force on the truck. E.The mosquito exerts a force on the truck but the truck does not exert a force on the mosquito. 2015 Pearson Education, Inc. Slide 4-22 QuickCheck 4.17 A mosquito runs head-on into a truck. Splat! Which is true during the collision? A.The mosquito exerts more force on the truck than the truck exerts on the mosquito. B.The truck exerts more force on the mosquito than the mosquito exerts on the truck. C.The mosquito exerts the same force on the truck as the truck exerts on the mosquito. D.The truck exerts a force on the mosquito but the mosquito does not exert a force on the truck. E.The mosquito exerts a force on the truck but the truck does not exert a force on the mosquito. 2015 Pearson Education, Inc. Slide 4-23 Summary: General Principles 2015 Pearson Education, Inc. Text: p. 118 Slide 4-24 Summary: General Principles 2015 Pearson Education, Inc. Text: p. 118 Slide 4-25 Summary: General Principles 2015 Pearson Education, Inc. Text: p. 118 Slide 4-26 Summary: Important Concepts 2015 Pearson Education, Inc. Text: p. 118 Slide 4-27 Summary: Important Concepts 2015 Pearson Education, Inc. Text: p. 118 Slide 4-28 Summary: Important Concepts 2015 Pearson Education, Inc. Text: p. 118 Slide 4-29 Summary: Applications 2015 Pearson Education, Inc. Text: p. 118 Slide 4-30 Summary: Applications 2015 Pearson Education, Inc. Text: p. 118 Slide 4-31 Summary 2015 Pearson Education, Inc. Text: p. 118 Slide 4-32 Summary 2015 Pearson Education, Inc. Text: p. 118 Slide 4-33 Summary 2015 Pearson Education, Inc. Text: p. 118