Forces and Motion Ch. 2.3 Reading

Section 3: Friction and Gravity

Newton's First Law of Motion

• An object at rest stays at rest; an object in motion stays in motion unless acted upon by unbalanced forces.

• Friction and gravity are crucial forces affecting motion.

  • Friction: Opposes motion and causes objects to stop.

  • Gravity: Pulls objects downward, causing them to accelerate.

Factors Affecting Friction

• Surface Type: Rough surfaces create greater friction than smooth surfaces.

• Normal Force: More force between surfaces increases friction.

• Types of friction:

  • Sliding Friction: Between sliding surfaces.

  • Rolling Friction: When an object rolls across a surface.

  • Fluid Friction: Movement through liquids or gases; generally less than sliding friction.

Usefulness of Friction

• Essential for walking, driving, and lighting matches.

• Can be increased or decreased depending on the situation (e.g. sand on icy ground).

Gravity

• Gravity pulls objects toward each other, particularly Earth.

• Free Fall: When only gravity acts on a falling object, leading to 9.8 m/s² acceleration.

• Terminal Velocity: The maximum velocity reached when air resistance equals gravitational pull.

Distinction Between Weight and Mass

• Weight: The force of gravity on an object (measured in newtons).

• Mass: The amount of matter in an object (measured in kilograms). Weight varies with gravitational pull.

  • Example: Weight on the moon is about one-sixth of weight on Earth.

Law of Universal Gravitation

• Every object attracts every other object with a force dependent on mass and distance.

• Distance weakens the gravitational force; closer objects exert a stronger gravitational pull.

Section Review Questions

1. List factors affecting friction strength when surfaces slide.

2. Define the difference between weight and mass.

3. Summarize the law of universal gravitation.

Chapter Project

• Create a diagram of a vehicle with labeled force arrows, including friction forces.