Linear Motion

• Linear Motion


  The movement of a body in a straight or curved line , where all parts move the same distance, in the same direction , over the same time.
• Linear motion results from a direct force being applied to a body, directly to the centre of mass.
• Key factors of Linear motion 


  1. Distance
  2. Displacement
  3. Speed
  4. Velocity
  5. Acceleration /Deceleration
• Distance is the total length of the path/route covered from start to finish.
• Displacement is the shortest straight line route from start to finish. units (m)
• Speed is the rate of change in distance. units (m/s)
• Velocity is the rate of change in displacement. units (m/s)
• If a body is travelling in a straight line then speed and velocity will be the same.
• Acceleration is the rate of change in velocity. units (m/s/s)
• Deceleration occurs when the rate of change of velocity is negative or there is a decrease in velocity over time.
• Speed(m/s) = Distance / Time taken
• Velocity (m/s) = displacement / time taken
• Acceleration = (final velocity - initial velocity) / time taken
• The key descriptors of linear motion can be plotted in 3 graphs 


  1. Distance / time graphs
  2. Speed / time graphs
  3. Velocity / time graphs
• The graphs can be used to identify patterns and calculate speed or acceleration.
• Distance time graphs 


  • Shows the distance a body travels over a period of time
  • The gradient shows the speed of the body at a particular instant in time.
  • It will indicate either constant speed, acceleration or deceleration.
• Deceleration - The rate of distance covered decreases

  
• Acceleration - the rate of distance covered increases

  
• Rest - No changes in distance as time increases.

  
• Constant speed - the rate of distance covered remains the same as time passes.

  
• Distance time graph showing the motion of a 100m sprinter.

  A) Rest

  B) Acceleration

  C) Constant velocity

  D) Deceleration

  
• Speed time graph

  
  

  0-A ~ constant speed

  A-B = shows acceleration ,speed increasing per unit of time from 10 m/s to 30m/s

  B-C = Shows constant speed

  C-D = shows deceleration, speed decreasing per unit of time from 30 m/s to 5 m/s

  
• Speed time graphs 


  • Show the speed of a body over a period of time
  • The gradient of the curve shows the acceleration of the body at a particular instant in time
  • Using the curve, distance covered can be measured as the area under the speed/time curve.
• Velocity time graphs 


  • Show the velocity of a body over a period of time
  • They can also show changes in direction
• Velocity time graph

  A = ski jumper is at rest

  A-B = An increase in velocity , the ski jumper is heading down the ramp

  B-C = The ski jumper reaches uniform velocity until takeoff

  C = takeoff

  
• A velocity time graph showing motion of a ball being passed between two players.

  A = the ball is in a stat of inertia

  A-B = acceleration

  B-C = Deceleration

  C- D = The body is in a state of inertia

  D - E = Acceleration

  E- F = Deceleration