Basic Concepts in Physics

Overview

• This video covers basic physics concepts: displacement, velocity, acceleration, projectile motion, Newton's laws, forces, momentum, etc.

Distance vs. Displacement

• Distance:

  • How far something has traveled (e.g. 100 miles between cities).
  • Scalar quantity (only magnitude).

• Displacement:

  • Change in position including direction.
  • Example with John:
    • Walks 8 m east, then 3 m west.
    • Total distance = 8 + 3 = 11 m.
    • Displacement = final position - initial position = 5 m.
  • Vector quantity (magnitude + direction).
  • Positive for east/north, negative for west/south.

Speed vs. Velocity

• Speed:

  • How fast something is moving (e.g. 30 m/s).
  • Scalar quantity (always positive).

• Velocity:

  • Speed with direction (e.g. 30 m/s north).
  • Vector quantity (can be positive or negative).
  • Speed = |velocity|, always positive.

Formulas

• Distance: D = VT
  • D = distance, V = speed, T = time.
• Average Speed:
  • Average speed = total distance / total time.
• Average Velocity:
  • Average velocity = displacement / total time.

Acceleration

• Definition:
  • Change in velocity over time (e.g. a = (final velocity - initial velocity) / time).
• Positive acceleration increases speed; negative acceleration (deceleration) decreases speed.
• Example:
  • Truck accelerates from 0 to 60 mph in 30 s (a = 2 mph/s).
  • Sports car accelerates from 0 to 60 mph in 5 s (a = 12 mph/s).

Gravitational Acceleration

• Earth's gravitational acceleration (g): -9.8 m/s².
• Affects vertical motion (not horizontal).
• Example of a ball dropped:
  • Initial velocity = 0; velocity becomes negative as it falls.

Projectile Motion

• Definition:
  • An object moving under gravity.
• Example of a ball dropped or thrown:
  • Two-dimensional motion: x and y components.
  • Horizontal velocity (vx) is constant; vertical velocity (vy) changes due to gravity.
• Initial velocity can be resolved into components:
  • Vx = V cos(theta); Vy = V sin(theta).

Newton's Laws of Motion

• First Law:
  • An object at rest stays at rest; an object in motion stays in motion unless acted on by a net force.
• Second Law:
  • F_net = m * a (net force = mass x acceleration).
  • Example: A 10 kg mass with an 80 N force accelerates at 8 m/s².
• Third Law:
  • For every action, there is an equal and opposite reaction. (Not detailed in the transcript but commonly included in Newton's laws).

Key Takeaways

• Understand the distinction between scalar and vector quantities.
• Apply the relevant formulas for motion concepts.
• Grasp the implications of acceleration and Newton's laws on motion.