motion

• Physical quantities measured by scientists fall into two categories: scalars and vectors
• Scalars:

  • Have magnitude (size) only
  • Examples include energy, temperature, mass, distance
• Vectors:

  • Have magnitude and direction
  • Examples include displacement, velocity, acceleration, force, weight
• Speed is a scalar quantity where direction is not important
• Velocity is a vector quantity where direction is important
• Scalar quantities likely used in Physics:

  • Mass
  • Distance
  • Speed
  • Rate of change of speed
  • Time
• Vector quantities likely used in Physics:

  • Displacement
  • Velocity
  • Acceleration
  • Force
  • Weight
• The force on an object is the product of its mass and acceleration.
• Average speed =   Total distance / Total time taken (m/s)
• The only difference between velocity and speed is that velocity has a direction, and so is a vector quantity.
• Average velocity = displacement/ time
• Displacement is the distance moved in a straight line, in a given direction, from the starting point.

  Displacement is a vector quantity as it has sizeand direction.
• average velocity

  av= displacement/ time

  av= (initial v + final v)/2
• A horizontal line on a distance-time graph shows that the object is stationary (not moving because the distance does not change)

  A sloping line on a distance-time graph shows that the object is moving.
• If the speed of an object changes, it will be accelerating or decelerating
• Displacement-time graphs show how the displacement of a moving object changes with time.
• A horizontal line on a displacement-time graph shows that the object is stationary (not moving because the displacement does not change)

  A sloping line on a displacement-time graph shows that the object is moving.
• In a displacement-time graph, the slope or gradient of the line, is equal to the velocity of the object.

  The steeper the line (and the greater the gradient) the faster the object is moving.
• The gradient of a displacement–time graph = velocity
• acceleration= change in velocity/time taken to change velocity (m/s2)

  a=(v-u)/t
• Gradient of speed-time graph = acceleration (m/s2)

  Area under speed-time graph = distance travelled (m)
• in a velocity/time graph...

  • Constant acceleration is shown by a straight rising line.
  • Constant retardation (or deceleration) is shown by a straight falling line, .
  • Constant velocity is shown by a horizontal line,
  • A horizontal line along the X-axis shows the speed is zero, meaning that the vehicle has stopped, or is stationary