Motion
Physics · गति
📋Quick Overview
Motion means change in position of an object with respect to time. If a thing changes its position, it is in motion. If it doesn't, it is at rest. Everything around us is in motion — the Earth rotates, cars move, blood flows in our body. Motion is the most basic topic of mechanics in physics.
Motion is RELATIVE — a person sitting in a moving train is at rest w.r.t. the train but in motion w.r.t. the ground. This is why we say 'motion depends on the frame of reference'.
📖Distance vs Displacement
📖Speed vs Velocity
Conversion: 1 km/h = 5/18 m/s (divide by 3.6). So 36 km/h = 10 m/s. To convert m/s to km/h, multiply by 18/5.
📖Acceleration & Equations of Motion
Acceleration = rate of change of velocity. If a car speeds up from 0 to 60 km/h, it is accelerating. If it slows down, it is decelerating (negative acceleration). Formula: a = (v - u) / t, where u = initial velocity, v = final velocity, t = time.
| Equation | Formula | When to Use |
|---|---|---|
| 1st Equation | v = u + at | When displacement (s) is NOT given |
| 2nd Equation | s = ut + ½at² | When final velocity (v) is NOT given |
| 3rd Equation | v² = u² + 2as | When time (t) is NOT given |
Remember: u = initial velocity, v = final velocity, a = acceleration, t = time, s = displacement. These 3 equations work ONLY for uniform acceleration (constant acceleration).
📝Types of Motion
- •Uniform Motion — equal distance in equal time (constant speed). Example: Earth revolving around Sun
- •Non-uniform Motion — unequal distance in equal time (speed changes). Example: car in city traffic
- •Linear Motion — motion in a straight line. Example: ball falling down, train on straight track
- •Circular Motion — motion in a circle. Example: Earth around Sun, fan blades, merry-go-round
- •Oscillatory/Vibratory Motion — to and fro motion. Example: pendulum, swing, guitar string
- •Rotational Motion — spinning around an axis. Example: spinning top, Earth on its axis
- •Projectile Motion — object thrown at an angle. Example: ball thrown by a cricketer, bullet fired from gun. Path is parabolic.