Kinematics

• Distance is the total length moved irrespective of direction
• Displacement is the shortest point from one point to another in a particular direction
• Speed is the rate of change of distance per unit time
• Velocity is the rate of change of displacement per unit time
• Average speed/velocity is the average rate of change of distance/displacement over a unit period of time
• Instantaneous velocity/speed is the velocity/speed of an object at any particular instant of time
• Acceleration is the rate of change of velocity per unit time
• Acceleration of free fall is the acceleration produced when an object falls under the influence of the gravitational force of the earth alone
• The equation for acceleration due to gravity is g = -9.81 m/s^2
• Projectile motion is the motion of an object thrown or projected into the air, subjected only to the acceleration of gravity
• Equations of motion can only be applied for,

  • motion in straight line
  • constant acceleration
• 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 light beam and the timer stops
  • vertical distance h is plotted against t squared
• Projectile motion is when the uniform velocity acts along the horizontal direction and constant acceleration acts in a perpendicular direction
• In projectile motion,

  • without air resistance, the horizontal direction is constant, and the vertical direction increases at a constant rate
  • with air resistance, the horizontal direction decreases to 0, and vertical direction increases to a constant value
• Terminal velocity,

  • for a body in free fall, the only force acting on it is its weight and its acceleration
  • drag force increases as the body accelerates
  • therefore, the acceleration decreases
  • when the drag force is equal to the gravitational pull on the body, the body will no longer accelerate and will fall at a constant velocity
  • this is the maximum velocity that the object can have an is called the terminal velocity