Physics Basics: Key Concepts

Overview

• Topics Covered: Distance, Displacement, Speed, Velocity, Acceleration, Newton's Laws, Forces, Momentum, Projectile Motion
• Purpose: Introduce basic principles of physics.

Distance vs. Displacement

• Distance: How far something has traveled (scalar quantity).
  • Example: A car travels 11 meters (8 meters east + 3 meters west).
• Displacement: Distance with direction (vector quantity).
  • Example: Net displacement: 5 meters (8 meters east - 3 meters west).
• Key Points:
  • Distance: Always positive.
  • Displacement: Can be positive or negative depending on direction.

Scalar vs. Vector Quantities

• Scalar: Only magnitude (e.g., distance, speed).
• Vector: Magnitude and direction (e.g., displacement, velocity).

Speed

• Definition: How fast something is moving (scalar).
• Formula: d = vt
  • d = distance, v = speed, t = time
• Example: A car at 30 meters/second will cover 30 meters in one second.
• Calculation Example:
  • Speed = 50 m/s; Distance = 1000 m; Time:
  t = d/v = 1000/50 = 20 seconds

Speed vs. Velocity

• Speed: Scalar (always positive).
• Velocity: Vector (can be positive or negative).
• Formulas:
  • Average Speed:
  v = d/t (Total distance/Total time)
  • Average Velocity:
  v = displacement/t

Acceleration

• Definition: How fast velocity changes (rate of change of velocity).
• Formula: a = (v final - v initial) / t
• Example: Sports car goes from 0 to 60 mph in 5 seconds: a = 60/5 = 12 mph/s

Speeding Up vs. Slowing Down

• Object speeds up when velocity and acceleration have same signs.
• Object slows down when velocity and acceleration have opposite signs.
  • Example: Positive velocity and positive acceleration = speeding up.
  • Negative velocity and positive acceleration = slowing down.

Gravitational Acceleration

• Earth: g = -9.8 m/s² (affects vertical component of velocity).
• Example:
  • Object dropped from rest:
  v_y decreases by 9.8 m/s each second.
• Vertical vs. Horizontal Components:
  • Gravitational acceleration does not affect horizontal velocity.

Projectile Motion

• Definition: Object under the influence of gravity (both x and y directions).
• Components:
  • Horizontal (vx): remains constant (no horizontal acceleration).
  • Vertical (vy): changes due to gravitational acceleration.
• Example:
  • Ball kicked off a cliff at 5 m/s horizontal speed.
  • Vertical speed decreases by 9.8 m/s² each second.
• Trajectory: Path of the projectile. Horizontal motion is constant, vertical motion changes.

Newton's Three Laws

1. First Law (Inertia):

• Object at rest stays at rest; object in motion stays in motion unless acted on by a force.
  • Example: Box at rest moves only if a force is applied.

2. Second Law (F = ma):

• Net force on an object equals its mass times acceleration.
  • Example: 10 kg mass on a surface with an 80 N force:

3. Third Law:

• Every action has an equal and opposite reaction.

Summary

• Distance: Scalar, path traveled.
• Displacement: Vector, direct path between start and end.
• Speed/Velocity: Speed (scalar), velocity (vector).
• Acceleration: Change in velocity over time.
• Projectile Motion: Motion in x and y direction under gravity.
• Newton's Laws: Fundamental principles governing motion.