Describing Motion

Key Notes:

Definition of Motion:

  • Motion occurs when an object changes its position relative to a reference point over time.

Types of Motion:

  • Linear Motion: Movement in a straight line (e.g., a car moving on a road).
  • Circular Motion: Movement in a circular path (e.g., the motion of a ceiling fan).
  • Rotational Motion: Motion of an object around its axis (e.g., Earth’s rotation).
  • Oscillatory Motion: Back-and-forth motion (e.g., a pendulum).

Reference Point:

  • A fixed point used to determine the position of a moving object.
  • Motion is always described relative to this reference point.

Distance and Displacement:

  • Distance: The total path length traveled, a scalar quantity (only magnitude).
  • Displacement: The shortest straight-line distance between the initial and final positions, a vector quantity (magnitude and direction).

Speed and Velocity:

  • Speed: The rate at which distance is covered (scalar quantity).

Speed = Distance / Time

  • Velocity: The rate at which displacement occurs (vector quantity).

Velocity = Displacement / Time

  • Uniform motion has constant speed/velocity, while non-uniform motion involves changing speed/velocity.

Acceleration:

  • The rate of change of velocity over time.

Acceleration = Change in Velocity / Time Taken

  • Positive acceleration indicates increasing velocity; negative acceleration (deceleration) indicates decreasing velocity.

Graphical Representation of Motion:

  • Distance-Time Graph: Slope represents speed. A straight line indicates uniform motion.
  • Velocity-Time Graph: Slope represents acceleration. The area under the graph gives displacement.

Equations of Motion (For Uniformly Accelerated Motion):

First equation: v = u + at

Second equation: s = ut + 1/2 at2

Third equation: v2 = u2 + 2as Where:

  • v: Final velocity
  • u: Initial velocity
  • a: Acceleration
  • s: Displacement
  • t: Time

Relative Motion:

  • Motion of an object observed from another moving or stationary reference point.
  • Important for understanding relative speed in cases like vehicles moving in opposite or the same direction.

Examples of Motion:

  • Walking, flying an airplane, Earth’s orbit around the Sun.

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