Physics Lecture Notes

Understanding Physical Quantities

• Types: Scalar and Vector
  • Scalar Quantity: Only magnitude (e.g., Volume, Mass, Speed)
    • Example: Volume of 150 cubic meters
  • Vector Quantity: Magnitude and direction (e.g., Weight, Force)
    • Example: Weight of 500 Newtons (downward)

Displacement vs. Distance

• Distance: Scalar
  • Path traveled (e.g., half circumference for A to B)
  • Total length (e.g., full circumference for return to point A)
• Displacement: Vector
  • Straight line from start to end
  • Directional (e.g., diameter or zero when returning to start)

Speed and Velocity

• Speed: Scalar
  • Distance moved per unit time (m/s)
• Velocity: Vector
  • Speed with direction (m/s)
  • Equal to speed if direction is constant

Acceleration

• Definition: Change in velocity per unit time
• Formula: a = (V - U) / t
  • Units: m/s²
  • Positive for acceleration, negative for deceleration

Motion Experiments

• Toy Car Experiment: Relationship between track height and average speed
  • Measure height, distance, and time
  • Calculate average speed: Distance / Time

Graphical Analysis

• Distance-Time Graph:
  • Gradient represents speed
  • Horizontal line: At rest
  • Straight line: Constant speed
• Velocity-Time Graph:
  • Gradient represents acceleration
  • Area under graph = distance moved

Forces

• Types: Contact and Non-contact
  • Contact Forces: Friction, Tension, Normal Force
  • Non-contact Forces: Gravitational, Electrostatic, Magnetic
• Resultant Force: Sum of all forces acting on an object
  • Zero resultant: Balanced (object at rest or constant speed)
  • Non-zero resultant: Unbalanced (object accelerates)

Newton's Laws of Motion

1. First Law: Balanced forces mean no change in motion
2. Second Law: F = ma (force causes acceleration)
3. Third Law: Every action has an equal and opposite reaction

Stopping Distance

• Total stopping distance = Reaction distance + Braking distance
• Factors: Speed, Mass, Road conditions, Reaction time

Free Fall and Terminal Velocity

• Free Fall: Only gravity acts, constant acceleration (10 m/s²)
• Terminal Velocity: Balance of forces, constant speed
• Sky Diver Example: Acceleration decreases as drag force increases

Deformation and Hooke's Law

• Hooke's Law: Extension is proportional to force until elastic limit
• Elastic vs. Plastic Deformation
  • Elastic: Returns to original shape
  • Plastic: Permanent deformation

Momentum

• Definition: Product of mass and velocity
• Conservation of Momentum: Total momentum before = Total momentum after

Safety Features in Vehicles

• Increase collision time to reduce force impact
  • Crumple zones, Airbags, Seatbelts

Moments and Equilibrium

• Moment of Force: Force * perpendicular distance from pivot
• Principle of Moments: Total clockwise moments = Total anticlockwise moments for equilibrium*

Center of Gravity

• Point where weight appears to act

Remember: Concepts like acceleration, momentum, and forces are interrelated and understanding graphs and experiments can help visualize these relationships.