Unit 2: Kinematics

• Speed is defined as the rate of change of distance
• Equation used to calculate speed: speed = distance / time
• Respective SI units for speed: m s^-1
• Displacement of an object is the distance it has travelled in a given direction, making it a vector with both magnitude and direction
• Velocity of an object is defined as the rate of change of displacement, or speed in a given direction, making it a vector
• Equation used to calculate velocity: velocity = change in displacement / time
• Respective SI units for velocity: m s^-1
• Acceleration is defined as the rate of change of velocity, making it a vector
• Equation used to calculate acceleration: acceleration = change in velocity / time
• Respective SI units for acceleration: m s^-2
• To find the gradient of a straight line on a graph:

  • Take a portion of the line
  • Measure the horizontal and vertical length of that portion
  • Gradient = vertical length / horizontal length
• On a displacement-time graph, a straight, horizontal line represents a stationary object
• On a displacement-time graph, a line with a constant, non-zero gradient represents an object moving with constant velocity
• On a displacement-time graph, a curved line represents acceleration (if gradient is increasing) or deceleration (if gradient is decreasing)
• On a velocity-time graph, a straight, horizontal line represents an object moving with constant velocity
• On a velocity-time graph, a line with a constant, non-zero gradient represents an object that is moving with a constant acceleration (positive gradient) or deceleration (negative gradient)
• The area under a velocity-time graph represents displacement
• The area under an acceleration-time graph represents velocity
• To determine the acceleration of an object under gravity using light gates:

  • Set up light gates vertically and measure the distance between them
  • Connect them to a data logger
  • Release an object from rest above them and measure the velocity using the light gates
  • Calculate the acceleration of the falling object using the velocities and known distance
• Horizontal velocity of a ball projected off a castle at 6 m/s remains the same until it hits the ground, provided air resistance is negligible
• In projectile motion, the vertical acceleration is equal to gravitational field strength (g), acting downwards
• The 5 SUVAT equations:

  • s = ut + 1/2at^2
  • v = u + at
  • v^2 = u^2 + 2as
  • s = vt - 1/2at^2
  • s = 1/2(u+v)t
  • s is displacement, v is final velocity, u is initial velocity, a is acceleration, t is time taken