SC 7.2

• Potential energy

  • Energy stored in the object because of its position, condition or shape
  • Two types of potential energy
  • Gravitational potential energy
  • Elastic potential energy
• Gravitational potential energy

  • The work done to lift an object to a height, h, from the Earth's surface
  • Potential energy stored in the object because its higher position from ground
  • Ground level = 0 GPE
• Relationship between Work and GPE

  • Work done that is against the gravitational force is known as GPE
  • When a box lifted to a certain height from surface of Earth, work is done to oppose gravitational force
  • GPE = work done
  • GPE = Force * Displacement
  • GPE = (mass (Kg) * gravitational acceleration (m/s*s)) * Displacement (m)
  • GPE = mgh
• Quantity of GPE depends on the

  • mass of objects
  • distance of objects
  • Strength of the Earth's gravitational field on the object
• Amount of GPE increases

  • Mass of object increases
  • Height of object from surface of Earth increases
  • Gravitational strength increases
• Benefits of GPE

  • A swimmer can dive easily into the water from an elastic board
  • Kids can slide down easily
  • Water in a dams can move faster to turn turbines to generate electrical energy in hydroelectric power stations
• Elastic potential energy

  • energy stored as a result of deformation of an elastic object as it is compressed or stretched
  • Example
  • "Slinky" - when stretched or compressed
  • Spring - when stretched or compressed
  • Rubber band - when stretched
  • Balloon with air - when stretched or compressed
• Relationship between work and EPE

  • Energy is needed to compress and stretch elastic objects such as springs and elastic bands
  • Elastic object gain energy when work is applied on it by compressing or stretching it, the energy is known as EPE
  • EPE = Amount of work done
  • The force required to stretch a spring to a certain distance (displacement from the equilibrium position, x) increase uniformly with distance
  • EPE = Average force * displacement
  • EPE = 1/2(Force) * x
  • EPE = 1/2(Fx)
• Kinetic energy

  • Energy possessed by an object due to its motion
  • The amount of KE on a moving object depends on
  • Mass of the moving object
  • Speed
  • If the mass of the object increases and its speed increases, thus the kinetic energy increases
  • The amount of KE of an object in motion is determined using : KE (J) = 1/2 * Mass (kg) * (speed^2) (m/s)
  • KE = 1/2*mv^2
• KE and work done

  • Newton's First Law : An object will remain in its motion unless a force acts upon it to change the motion
  • According to Newton's First Law of motion, an object that moves at a constant speed will maintain its kinetic energy
  • Work is done when the KE of a moving object increases or decreases
  • The change in the KE of an object is similar to the work done on the object
  • Work = Change in kinetic energy
  • Work = Final KE - Initial KE