Basic Physics Concepts

Topics Covered

• Displacement
• Velocity
• Acceleration
• Projectile Motion
• Newton's Three Laws
• Forces
• Momentum

Distance and Displacement

• Distance: How far something has travelled. Scalar quantity (magnitude only).
  • Example: Distance between two cities could be 100 miles.
• Displacement: Distance + Direction. Vector quantity (magnitude and direction).
  • Example: John walks 8 meters east, then 3 meters west.
    • Total distance = 11 meters
    • Displacement = 5 meters (8 - 3)
• Scalar Quantity: Only magnitude.
• Vector Quantity: Magnitude and direction.
• Displacement can be positive or negative based on direction.

Speed vs. Velocity

• Speed: How fast something is moving. Scalar quantity (positive).
  • Example: 30 meters per second means every second an object travels 30 meters.
  • Formula: d = vt
• Velocity: Speed with direction. Vector quantity (can be positive or negative).
  • Example: 30 meters per second going west.
  • Average Speed: total distance / total time
  • Average Velocity: displacement / total time
• Formulas:
  • Average Speed: v̄ = d / t
  • Average Velocity: v̄ = Δx / t

Acceleration

• Acceleration: How fast velocity is changing. Vector quantity.
  • Formula: a = Δv / Δt
  • Example: Sports car vs. truck accelerating from 0 to 60 mph.
• Acceleration due to Gravity (g): Vertical acceleration affecting velocity.
  • On Earth: g = -9.8 m/s²
  • Affects vertical component of velocity, not horizontal.
  • Formulas:
    • v_f = v_i + at
    • Gravitational Acceleration: Examples:
      • Object released from rest: Vertical velocity continuously decreases.
      • Object thrown upwards: Vertical velocity decreases by 9.8 m/s every second.

Projectile Motion

• Projectile: Object moving under gravity's influence.
  • One-Dimensional Motion: Vertical direction (y-direction).
    • Examples: Ball falling or thrown straight up.
  • Two-Dimensional Motion: Horizontal (x-direction) and vertical (y-direction).
    • Example: Ball rolling off a cliff or kicked at an angle.
  • Horizontal velocity (v_x) remains constant, vertical velocity (v_y) changes due to gravity.
  • Formulas:
    • v_y = v sin(θ)
    • v_x = v cos(θ)

Newton’s Three Laws of Motion

• First Law: Object at rest stays at rest, object in motion stays in motion unless acted on by an external force.
  • Example: Box remains still unless a push or pull force is applied.
• Second Law: F = ma
  • Example: 10 kg box with 80 N force → acceleration = 8 m/s²
    • Velocity increases by 8 m/s every second if the force is continuously applied.
• Third Law (Implied but not detailed in transcript): Every action has an equal and opposite reaction.