Motion in a Straight Line

Motion in a Straight Line

1. Position, path length/distance, and displacement

   • Position: it changes with reference to the frame of reference.
   • Distance: also called path length. Length of the actual path traversed by a body between initial and final positions.
     • SI unit is metre Scalar quantity
   • Displacement: the shortest distance between the final and initial positions
     • SI unit is metre Vector quantity. Can become zero, negative or positive

2. Speed

   • distance travelled by an object in unit time. Distance travelled/ time taken SI unit is metre/second (m/s-1)
   • Uniform speed: object moving with uniform speed at uniform intervals of time.
   • Average speed: total distance travelled/total time taken
   • Instantaneous speed: describes how fast an object is moving at different instants of time

3. Acceleration

   • Rate of change of velocity of an object with time Vector quantity. Has the same direction as that of change in velocity. SI unit in m/s-2
   • Uniform acceleration: change in velocity of the object is equal in equal intervals of time.
   • Instantaneous acceleration: acceleration of an object at a given instant of time

4. Free fall

   • An object falling because of earth’s gravity. On neglecting the air resistance, this is a case of uniform acceleration.
   • V= u+gt S= ut + ½ at2 V2= u2 + 2as

5. Graphs

   • Displacement time graph:
     • • Slope is equal to velocity
     • • Constant velocity is explained by the straight line while acceleration is explained by the curved lines.
     • • Positive slope means the motion is in the positive direction.
     • • Negative slope means the motion is in the negative direction.
     • • Negative slope means the motion is in the negative direction.
   • Velocity time graphs
     • • Slope of the graph gives acceleration. • Steep slope represents the rapid change in velocity.
     • • Shallow slope represents the slow change in velocity. • If the slope is negative, then the acceleration will also be negative.
     • • If the slope is positive, then the acceleration will also be positive. • The area under the velocity, represents the displacement of the object
   • Acceleration time graph
     • • If slope is zero, then the motion is said to have constant acceleration. • The area under the graph represents the change in velocity

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