Kinematics

Kinematics Concepts

  • Distance: total length moved irrespective of direction

  • Displacement: shortest distance in a certain direction

  • Speed: distance traveled per unit of time, no direction

  • Velocity: the rate of change of displacement

  • Acceleration: the rate of change of velocity

Equations of Motions

s=ut+12at2s=ut+21​at2

v=u+atv=u+at

v2=u2+2asv2=u2+2as

s=(v1+v2)2×ts=2(v1​+v2​)​×t

Linear Motion

  • Distance: total length moved irrespective of direction

  • Displacement: distance in a certain direction

  • Speed: distance traveled per unit of time, no direction

  • Velocity: the rate of change of displacement

  • Acceleration: the rate of change of velocity

  • Displacement-time graph:

    • Gradient = velocity

Non-Linear Motion

Velocity-time graph:

  • Gradient = acceleration

  • The area under graph = change in displacement

Uniform acceleration and straight-line motion equations:

v=u+atv=u+at

s=ut+12at2s=ut+21​at2 =vt−12at2=vt−21​at2

s=12(u+v)ts=21​(u+v)t

v2=u2+2asv2=u2+2as

  • Acceleration of free fall = 9.81ms-2

Motion of Freefalling Bodies

Displacement

Continues to curve as it accelerates

http://physics-ref.blogspot.com/2015/08/kinematics-9702-physics-summary-notes.html

Graph levels off as it reaches terminal velocity

Velocity

Continues to accelerate constantly

http://physics-ref.blogspot.com/2015/08/kinematics-9702-physics-summary-notes.html

Graph curves as it decelerates and levels off to terminal velocity

Acceleration

Straight line

Graph curves down to zero because the resultant force equals zero

http://physics-ref.blogspot.com/2015/08/kinematics-9702-physics-summary-notes.html

Determining Acceleration of Free Fall

  • A steel ball is held on an electromagnet.

  • When the electromagnet is switched off, the ball interrupts a light beam, and a timer starts.

  • As the ball falls, it interrupts a second beam of light & timer stopped

  • Vertical distance hh is plotted against t2t2

s=ut+12at2s=ut+21​at2 and u=0u=0 ; s=12at2s=21​at2 i.e h=12gt2h=21​gt2

Projectile motion

Projectile motion: uniform velocity in one direction and constant acceleration in perpendicular direction

  • Horizontal motion = constant velocity (speed at which projectile is thrown)

  • Vertical motion = constant acceleration (caused by the weight of the object, constant free fall acceleration)

  • Curved path – parabolic (y∝x2)(y∝x2)

Component of Velocity

Horizontal

Vertical

Without air Resistance

Constant

Increases at a constant rate

With Air resistance

Decreases to zero

Increases to a constant value

Motion of a Skydiver

Physical