Physics Basics Lecture Notes

Jul 20, 2024

Physics Basics Lecture Notes

Overview

  • Topics Covered:
    • Displacement
    • Velocity
    • Acceleration
    • Projectile Motion
    • Newton's Laws of Motion
    • Forces
    • Momentum

Distance and Displacement

  • Distance: Scalar quantity; total path length traveled; always positive.
    • Example: 100 miles between two cities.
  • Displacement: Vector quantity; has both magnitude and direction.
    • Example: John walks 8 meters east, then 3 meters west.
      • Total distance: 11 meters.
      • Displacement: 5 meters (East).

Scalars vs Vectors

  • Scalar Quantity: Magnitude only.
    • Example: Distance (200 miles).
  • Vector Quantity: Magnitude and direction.
    • Example: Displacement (300 miles North).

Speed and Velocity

  • Speed: Scalar quantity; how fast something is moving; always positive.
    • Example: Car travels at 30 meters per second.
    • Formula: d = vt.
  • Velocity: Vector quantity; speed with direction; can be positive or negative.
    • Example: Train moving at 30 meters per second West.
    • Average Speed: v = d / t
    • Average Velocity: v = Δdisplacement / t

Acceleration

  • Acceleration: Tells how fast velocity is changing.
    • Example: Sports car has greater acceleration than a truck.
    • Formula:
      • a = Δvelocity / t
      • a = (vf - vi) / t
  • Positive Acceleration: Velocity is increasing.
  • Negative Acceleration (Deceleration): Velocity is decreasing.

Gravitational Acceleration

  • Earth: g = -9.8 m/s²
    • Affects the vertical (y) component of velocity.
    • Example: Ball thrown upwards slows down, stops at peak, and falls down.
  • Moon: g = -1.6 m/s²

Projectile Motion

  • One-dimensional: Only in y direction (e.g., ball falling or thrown upwards).
  • Two-dimensional: In x and y direction (e.g., ball kicked off a cliff).
    • Horizontal component (vx) is constant.
    • Vertical component (vy) changes due to gravitational acceleration.

Newton's Laws of Motion

  • First Law: An object at rest stays at rest, and an object in motion stays in motion unless acted on by a net force (law of inertia).
  • Second Law: The net force on an object is equal to the mass times its acceleration.
    • Formula: F = ma
  • Third Law: For every action, there's an equal and opposite reaction.

Example Problems

  1. Calculate the time to travel 1000 meters at 50 meters per second:
    • Formula: d = vt
    • Solution: t = d / v = 1000 / 50 = 20 seconds
  2. Acceleration of a truck and a sports car:
    • Truck: a = 60 mph / 30 s = 2 mph/s
    • Sports car: a = 60 mph / 5 s = 12 mph/s
  3. Average speed and velocity:
    • Object travels 12m East, then 20m West in 4 seconds.
    • Average speed: (12 + 20) / 4 = 8 m/s
    • Average velocity: (12 - 20) / 4 = -2 m/s