Lecture on Motion

Introduction

• Topic: Motion
• Part of General Physics
• Focus on:
  • Speed and velocity
  • Acceleration
  • Graph interpretation

Speed

• Definition: Change in distance per unit time
• Formula: Speed = Total distance / Total time
• Example: 100m race in 10s gives a speed of 10 m/s

Velocity

• Definition: Change in displacement per unit time
• Difference from Speed:
  • Speed: Scalar quantity (magnitude only)
  • Velocity: Vector quantity (magnitude and direction)
• Example:
  • Travel from point A to B and back to A (500m each way)
  • Total distance = 1000m; Time = 2000s; Speed = 0.5 m/s
  • Displacement = 0 (back to starting point); Velocity = 0

Acceleration

• Definition: Change in velocity per unit time
• Formula: Acceleration = Change in velocity / Time taken
• Types:
  • Positive Acceleration: Increase in velocity over time
  • Negative Acceleration (Deceleration): Decrease in velocity over time
• Example: Acceleration from 100 m/s to 300 m/s

Free Fall and Gravity

• Acceleration due to Gravity: 9.8 m/s² on Earth
• Terminal Velocity: Constant speed where gravity is balanced by air resistance

Graph Interpretation

Displacement-Time Graph

• Shows: Displacement per unit time
• Interpretation:
  • Upward slope: Increasing displacement, indicates velocity
  • Horizontal line: Stationary object
  • Downward slope: Returning to start (negative displacement)

Speed-Time Graph

• Shows: Speed on y-axis, time on x-axis
• Interpretation:
  • Area under graph = Distance traveled
  • Gradient = Acceleration
  • Flat line: Constant speed, zero acceleration

Examples:

• Accelerating Car:
  • Steep gradient at start: High acceleration
  • Plateau: Constant speed
• Runner:
  • Initial acceleration
  • Plateau: Maximum speed
  • Slows down: Deceleration, stops
• Skydiver:
  • Initial acceleration, reduced by air resistance
  • Parachute opens: Rapid deceleration
  • Terminal velocity: Constant speed

Conclusion

• Key terms: Speed, velocity, acceleration, terminal velocity
• Importance of understanding graph interpretations
• For questions, engage in comments or check resources on Patreon.