Chapter 12 Notes: Forces and Motion

Chapter 12: Forces and Motion

Introduction

  • A scenario of a kayaker using a paddle to navigate downstream introduces the topic of forces.

  • Discussion of forces involved in a car crash, highlighting the unbalanced forces on both the car and the passengers.

  • Emphasis on planning a video presentation that will include a simulation of a car crash to illustrate forces via pauses for explanation.

Indiana’s Academic Standards for Science

Motion and Energy of Macroscopic Objects

  • ICP.1.2: Describe and apply Newton’s three laws of motion.

    • Through experimentation, determine relationships among mass, acceleration, and force.

    • Introduction to momentum and energy definitions.

  • ICP.1.3: Describe how Newton’s law of universal gravitation and laws of motion explain motions of objects on Earth, the moon, and celestial bodies.

Electrical Energy Propagation and Magnetism

  • ICP.6.6: Explain that magnets exert magnetic forces without direct contact.

Main Questions

  • Why does tug of war not always result in motion? (Section 12.1)

  • Why do flying squirrels spread out when jumping? (Section 12.1)

  • What happens to a passenger's forward motion in a head-on auto accident? (Section 12.2)

  • What factors affect the fall of a sky diver? (Page 370)

  • What stops a hammer’s head when driving a nail? (Section 12.3)

  • What causes tides? (Section 12.4)

Next Generation Sunshine State Standards

Nature of Science

  • SC.912.N.1.5: Similar investigations yield similar results.

  • SC.912.N.1.6: Scientific inferences are drawn from observations.

  • SC.912.N.1.7: Creativity in constructing scientific questions and methods.

Physical Science

  • SC.912.P.10.10: Compare the four fundamental forces.

  • SC.912.P.12.3: Interpret and apply Newton's laws of motion.

  • SC.912.P.12.4: Describe how gravitational force depends on mass and distance.

Additional Mathematics Requirements

  • MA.912.S.3.2: Collect and analyze data sets; present visual summaries.

Chapter Overview

12.1 Forces

  • Key Concepts: How do forces affect motion? What are the four main types of friction? How do gravity and air resistance affect falling objects?

  • Vocabulary:

    • Force, Newton, Net force, Friction, Static friction, Sliding friction, Rolling friction, Fluid friction, Air resistance, Gravity, Terminal velocity, Projectile motion.

  • Example scenario of weather conditions affecting movement, illustrating forces in action.

What is a Force?

  • Definition: A force is a push or a pull on an object.

    • Forces can initiate motion in a resting object or change the speed or direction of a moving object.

  • The effect of wind on a person as an illustration of force impacting motion.

Measuring Force

  • Forces can be measured using a spring scale.

    • Units: Force is measured in newtons (N). 1 N = 1 kg·m/s².

  • Definition of net force: Overall force acting on an object after combining all individual forces.

Combining Forces

  • Forces can be combined to create a larger force (e.g., many people pushing a car).

  • Net Force Calculation: Forces in the same direction add; in opposite directions, they subtract.

  • Balanced vs. Unbalanced Forces:

    • Balanced Forces: Produce a net force of zero, resulting in no motion change.

    • Unbalanced Forces: Cause acceleration in the direction of the net force.

Friction

  • Definition: Friction opposes motion between objects in contact.

  • Types of Friction:

    1. Static Friction: Acts on stationary objects, preventing motion until a sufficient force is applied.

    2. Sliding Friction: Acts on moving objects sliding over a surface.

    3. Rolling Friction: Significantly less force than static/sliding, present on rolling objects.

    4. Fluid Friction: Acts on objects moving through liquids or gases (includes air resistance).

Gravity

  • Definition: Gravity is an attractive force acting between masses.

  • Earth’s gravitational pull causes objects to accelerate downward (gravitational force always acts toward the center of the Earth).

  • Falling objects experience gravity and air resistance. Terminal velocity occurs when these two forces balance.

Summary of Key Points

12.2 Newton’s First and Second Laws of Motion

  • Newton’s First Law: Objects at rest remain at rest, and objects in motion continue in straight-line motion unless acted upon by an unbalanced force.

  • Newton’s Second Law: Acceleration is proportional to net force and inversely proportional to mass.

    a=Fma = \frac{F}{m}

  • Weight: Defined as the gravitational force acting on an object.

    W=mgW = mg where g=9.8 m/s2g = 9.8 \ m/s^2 on Earth.

12.3 Newton’s Third Law and Momentum

  • Newton’s Third Law: For every action, there is an equal and opposite reaction.

  • Momentum: Defined as the product of mass and velocity.

    Momentum=mvMomentum = mv

  • Conservation of Momentum: Total momentum in a closed system remains constant.

12.4 Universal Forces

  • Universal Forces:

    • Gravitational force, electromagnetic force, strong nuclear force, weak nuclear force.

  • Gravitational Force: Attracts two masses; weaker but acts at large distances; the basis for gravitational attraction between Earth and other objects.