CHAPTER 12 Study Guide

12.1 Forces

Key Concepts

• A force can cause a resting object to move, or it can accelerate a moving object by changing the object's speed or direction.

• When the forces on an object are balanced, there is no change in the object's motion. When an unbalanced force acts on an object, the object accelerates.

• There are four main types of friction: static friction, sliding friction, rolling friction, and fluid friction.

• Earth's gravity acts downward toward the center of Earth. Gravity causes objects to accelerate downward, whereas air resistance acts in the direction opposite to the motion and reduces acceleration.

• The combination of initial forward velocity and downward vertical force of gravity cause a projectile to follow a curved path.

Vocabulary

force, p. 356; newton, p. 357; net force, p. 357; friction, p. 359; static friction, p. 359; sliding friction, p. 359; rolling friction, p. 360; fluid friction, p. 360; air resistance, p. 360; gravity, p. 361; terminal velocity, p. 361; projectile motion, p. 362

12.2 Newton's First and Second Laws of Motion

Key Concepts

• According to Newton's first law of motion, the state of motion of an object does not change as long as the net force acting on the object is zero.

• According to Newton's second law of motion, the acceleration of an object is equal to the net force acting on it divided by the object's mass.

• Acceleration $=\genfrac{}{}{0.1ex}{}{Netforce}{Mass}$

• Momentum = × Acceleration due to gravity

• Mass is a measure of the inertia of an object;

Vocabulary

inertia, p. 364; mass, p. 365; weight, p. 368

12.3 Newton's Third Law of Motion and Momentum

Key Concepts

• According to Newton's third law of motion, forces exist as equal and opposite force pairs.

• Momentum = Mass × Velocity

  An object has a large momentum if the product of its mass and velocity is large.

• Momentum is conserved in a closed system.

Vocabulary

momentum, p. 374; law of conservation of momentum, p. 376

12.4 Universal Forces

Key Concepts

• Electric and magnetic forces are the only forces that can both attract and repel.

• The strong and weak nuclear forces hold the nucleus together.

• Newton's law of universal gravitation states that every object in the universe attracts every other object.

Vocabulary

electromagnetic force, p. 378; strong nuclear force, p. 379; weak nuclear force, p. 380; gravitational force, p. 380; centripetal force, p. 381

Thinking Visually

Concept Map Use the information on forces from the chapter to complete the concept map below.

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