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6: Applications of Newton's Laws

Car racing has grown in popularity in recent years. As each car moves in a curved path around the turn, its wheels also spin rapidly. The wheels complete many revolutions while the car makes only part of one (a circular arc). How can we describe the velocities, accelerations, and forces involved? What force keeps a racecar from spinning out, hitting the wall bordering the track? What provides this force? Why is the track banked? We answer all of these questions in this chapter as we expand our consideration of Newton’s laws of motion.

• 6.1: Prelude to Applications of Newton's Laws
Car racing has grown in popularity in recent years. As each car moves in a curved path around the turn, its wheels also spin rapidly. The wheels complete many revolutions while the car makes only part of one (a circular arc). How can we describe the velocities, accelerations, and forces involved? What force keeps a racecar from spinning out, hitting the wall bordering the track? What provides this force? Why is the track banked? We answer all of these questions in this chapter as we expand our c
• 6.2: Solving Problems with Newton's Laws (Part 1)
Newton’s laws of motion can be applied in numerous situations to solve motion problems. Some problems contain multiple force vectors acting in different directions on an object.
• 6.3: Solving Problems with Newton's Laws (Part 2)
Some motion problems contain several physical quantities, such as forces, acceleration, velocity, or position. You can apply concepts from kinematics and dynamics to solve these.
• 6.4: Friction (Part 1)
When a body is in motion, it has resistance because the body interacts with its surroundings. This resistance is a force of friction. Friction opposes relative motion between systems in contact but also allows us to move, a concept that becomes obvious if you try to walk on ice. Friction is a common yet complex force, and its behavior still not completely understood. Still, it is possible to understand the circumstances in which it behaves.
• 6.5: Friction (Part 2)
Simple friction is always proportional to the normal force. When an object is not on a horizontal surface, as with an inclined plane, the force acting on the object that is directed perpendicular to the surface needs to be found.
• 6.6: Centripetal Force
Centripetal force is a “center-seeking” force that always points toward the center of rotation so it is perpendicular to linear velocity. Rotating and accelerated frames of reference are noninertial. Inertial forces, such as the Coriolis force, are needed to explain motion in such frames.
• 6.7: Drag Force and Terminal Speed
Drag forces acting on an object moving in a fluid oppose the motion. For larger objects (such as a baseball) moving at a velocity in air, the drag force is determined using the drag coefficient, the area of the object facing the fluid, and the fluid density. For small objects (such as a bacterium) moving in a denser medium, the drag force is given by Stokes’ law.
• 6.E: Applications of Newton's Laws (Exercises)
• 6.S: Applications of Newton's Laws (Summary)

Thumbnail: Stock cars racing in the Grand National Divisional race at Iowa Speedway in May, 2015. Cars often reach speeds of 200 mph (320 km/h).