Physics Basics Lecture Notes

Introduction

• Overview of basic physics concepts: displacement, velocity, acceleration, projectile motion, Newton's laws, forces, momentum.

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Distance vs. Displacement

• Distance:

  • How far something has traveled (scalar quantity).
  • Example: Distance between cities is 100 miles.

• Displacement:

  • Difference between initial and final position, includes direction (vector quantity).
  • Example: John walks 8 m east and 3 m west:
    • Total distance = 8 + 3 = 11 m.
    • Displacement = Final position - Initial position = 5 m (8 - 3 = 5).

• Key Points:

  • Distance is always positive.
  • Displacement can be positive or negative depending on direction.
  • Displacement formula: (D = P_f - P_i)

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Speed vs. Velocity

• Speed:

  • The rate of motion (scalar quantity).
  • Example: Car traveling at 30 m/s means it covers 30 m every second.
  • Formula: (d = vt)
  • Average Speed = Total Distance / Total Time.

• Velocity:

  • Speed in a given direction (vector quantity).
  • Example: 30 m/s west.
  • Average Velocity = Displacement / Total Time.

• Key Differences:

  • Speed is always positive, while velocity can be negative if the direction is reversed.

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Acceleration

• Definition: Change in velocity over time.
• Formula: (a = (v_f - v_i)/t)
• Examples:
  • If a truck accelerates from 0 to 60 mph in 30 seconds, acceleration = 2 mph/s.
  • If a sports car accelerates from 0 to 60 mph in 5 seconds, acceleration = 12 mph/s.
• Acceleration can be positive (increasing speed) or negative (deceleration).

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Newton's Laws of Motion

1. First Law: An object at rest stays at rest and an object in motion stays in motion unless acted upon by a net force.
   • Example: A box on a frictionless surface continues moving unless a force is applied.
2. Second Law: The net force acting on an object is equal to the mass of the object times its acceleration ((F = ma)).
   • Example: A 10 kg mass under an 80 N force will have an acceleration of 8 m/s².

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Projectile Motion

• Definition: Motion of an object under the influence of gravity.

• Vertical motion influenced by gravitational acceleration ((g = -9.8 m/s²)).

• Horizontal velocity (v_x) remains constant unless acted on by another force.

• Example: Ball kicked off a cliff.

• Key notes on projectile motion:

  • horizontal motion: no acceleration (constant vx).
  • vertical motion: changing with g (varying vy).

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Conclusion

• Understanding these fundamental concepts in physics establishes a good foundation for further studies in the field.