Motion - U4

• Scalar

  A quantity which has a magnitude only
• Vector

  A quantity which has both magnitude and direction
• Vectors

  • displacement
  • velocity
  • acceleration
  • force
  • weight
• Distance

  The length of path covered
• Distance

  • It is a Scalar
  • It has SI unit metre (m)
• Displacement

  The straight line distance from a point in a specified direction
• Displacement

  • It is a vector
  • It has SI unit metre (m)
• If the path is linear (Straight)

  Magnitude of displacement is equal to distance
• If a body starts moving from a point and finally returned to the starting point

  Displacement is zero
• Scalars

  Length (distance)

  Time

  Mass

  Temperature

  Area

  Volume

  Work done

  All forms of energy

  Power

  Current

  Voltage

  Speed
• Speed

  • It is defined as the distance per unit time.
  • It is a scalar and has SI unit m/s
• Speed = distance/time
• Average speed = total distance/total time
• 1 m/s = 3.6 km/h
• If speed is constant, then average speed is equal to that constant speed
• If a body is at rest/stationary, the speed is 0.
• Velocity

  It is defined as the rate of change of displacement

  OR

  It is defined as the change in displacement per unit
• Velocity is a vector and has SI unit m/s.
• If a path is linear (straight), then magnitude of velocity is equal to speed.
• Velocity = displacement / time
• What is speed?

  It is defined as the distance per unit time
• Acceleration

  It is defined as the rate of change of velocity.

  OR

  It is defined as the change in velocity per unit time.
• • acceleration = change in velocity / time
  • acceleration = ( final velocity - initial velocity )/ time
  • a = ( v - u )/ t
• Acceleration is a vector and has SI unit m/s^2.
• Uniform acceleration

  The acceleration increases by a constant/same value.

  e.g: t=0, u=0

  t=1s, u=2m/s

  t=2s, u=4m/s

  t=3s, u=6m/s

  t=4s, u=8m/s

  
  

  a=2m/s (because it increases by 2m every second)
• Uniform Speed

  The speed is constant (does not change), hence a=0

  e.g: t=0, u=10m/s

  t=1s, v=10m/s

  t=2s, v=10m/s

  t=3s, v=10m/s

  t=4s, v=10m/s
• Non-uniform acceleration (increasing acceleration)

  The acceleration increases every second.

  e.g: t=0, u=0

  t=1s, v=2m/s (+2)

  t=2s, v=5m/s (+3)

  t=3s, v=10m/s (+5)

  t=4s, v=18m/s (+8)

  
  

  Do not write any value for a
• Speed-Time Graph

  It is a graph that shows how a body is moving. It describes the motion of an object or person.
• The gradient of speed-time graph gives the acceleration.
• The area under the graph gives distance.
• What can be deduced from a speed-time graph?

  1. whether the speed is uniform.
  2. whether the speed is increasing or decreasing.
  3. the distance travelled.