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