THIRD LAW MOTION.pptx

Introduction to Newton's Laws of Motion

  • Key focus on forces, interaction, and friction.

Objectives

  • Differentiate properties of static and kinetic friction.

  • Compute quantities such as frictional force, normal force, threshold angles for sliding, acceleration, etc.

  • Identify action-reaction pairs.

Newton’s Laws of Motion

Law #1

  • A body at rest will remain at rest, and a body in motion will remain in motion unless acted upon by an external force.

Law #2

  • The force acting on an object is equal to the mass of that object times its acceleration: F = ma.

Law #3

  • For every action, there is an equal and opposite reaction.

Understanding Action and Reaction Forces

General Interaction

  • Action and reaction occur when objects are in contact and collide.

  • There is always a pair of forces acting on objects.

Examples of Action and Reaction

  • Ball and Floor:

    • Action: The ball pushes the floor.

    • Reaction: The floor pushes the ball.

  • Hammer and Nail:

    • Action: The hammer pushes the nail.

    • Reaction: The nail pushes back on the hammer.

  • Balloon and Air:

    • Action: Air goes down.

    • Reaction: The balloon goes up.

  • Foot and Ground:

    • Action: The foot pushes the ground.

    • Reaction: The ground pushes back at the foot.

  • Bird and Air:

    • Action: The bird pushes air downwards.

    • Reaction: The air pushes the bird upwards.

  • Vase and Table:

    • Action: The vase pushes the table.

    • Reaction: The table pushes back at the vase.

Friction

Nature of Friction

  • Friction is a force that opposes the motion of an object or prevents stationary objects from moving.

  • It acts to slow down moving objects.

Causes of Friction

  • Friction arises when surfaces move over one another, causing grooves and ridges to catch, which slows motion.

Types of Friction

Static Friction

  • A force that keeps an object at rest; it must be overcome to start moving the object.

Kinetic Friction

  • Also known as sliding friction; it resists sliding or skidding between two surfaces.

Comparisons

  • Static friction operates between surfaces that aren't moving relative to each other.

  • Kinetic friction acts between objects in motion.

  • The direction of the friction force is always opposite to the direction of motion.

  • The magnitude of frictional force is directly proportional to the normal force.

  • Key Point: Static friction is always greater than kinetic friction.