Basic Concepts in Physics

Introduction

• Topics covered: Displacement, velocity, acceleration, projectile motion, Newton's three laws, forces, momentum.
• Goal: To provide a basic intro to physics and principle ideas.

Distance vs. Displacement

Distance

• Scalar quantity (magnitude only).
• Total path length traveled, always positive.
• Example: Traveling 11 meters (8 meters east + 3 meters west).

Displacement

• Vector quantity (magnitude + direction).
• Difference between initial and final positions.
• Example: 5 meters east (8 meters east - 3 meters west).
• Formula: Final position - Initial position.
• Positive when moving east or north; negative when moving west or south.

Speed

• Scalar quantity (always positive).
• Definition: How fast an object is moving.
• Formula: Speed (v) = Distance (d) / Time (t).
• Example: A car traveling 30 meters/second.

Velocity

• Vector quantity (magnitude + direction).
• Definition: Speed with direction.
• Can be positive or negative.
• Example: Train moving 30 meters/second west.
• Formula: Average velocity = Displacement (d) / Time (t).

Acceleration

• Definition: How fast the velocity is changing.
• Can be positive (increasing velocity) or negative (decreasing velocity).
• Formula: a = (Final velocity (Vf) - Initial velocity (Vi)) / Time (t).
• Example: Sports car vs. truck acceleration.

Key Points

• Same sign for velocity and acceleration = Speeding up.
• Opposite signs = Slowing down.

Gravitational Acceleration

• Earth: -9.8 m/s².
• Moon: -1.6 m/s².
• Affects vertical velocity (Vy), not horizontal velocity (Vx).
• Example: Object falling or thrown upward.

Projectile Motion

• Object moving under gravity's influence.
• Types: One-dimensional (vertical motion) and two-dimensional (horizontal motion with vertical fall).
• Horizontal velocity (Vx): Constant (unless external force acts).
• Vertical velocity (Vy): Changes due to gravity.

Examples

• Ball released from rest falls down (Vy becomes more negative).
• Ball thrown upward decreases in Vy till it changes direction.

Newton's Three Laws of Motion

First Law (Inertia)

• Object at rest remains at rest unless acted on by a force.
• Object in motion remains in motion unless acted on by a net force (e.g., friction).

Second Law (F=ma)

• Net force (F) = Mass (m) * Acceleration (a).
• Example: Applying force to a 10 kg mass.

Third Law (Action-Reaction)

• For every action, there is an equal and opposite reaction.

Summary

• Understand the differences between scalar (magnitude only) and vector (magnitude + direction) quantities.
• Key relationships: Distance vs. Displacement, Speed vs. Velocity, and the concept of acceleration.
• Newton's laws as fundamental principles governing the motion of objects.