MODULE 3

• Mechanical energy


  The sum of potential energy and kinetic energy of an object
• The total mechanical energy of a system is conserved
• Transformation of potential energy to kinetic energy

  1. Potential energy decreases

  2. Kinetic energy increases
• Conservation of mechanical energy


  • The sum of the potential energy and kinetic energy of an object is always the same regardless of the object's position
• Potential energy


  The energy that is stored due to an object's height
• Gravitational potential energy


  The potential energy of an object due to its height above a reference level or ground, given by mgh
• An object possesses greater gravitational potential energy the higher it is from the ground or reference level
• Kinetic energy


  The energy in motion, depends on mass and the square of velocity, given by 1/2 mv^2
• When velocity of an object doubles, its kinetic energy quadruples
• Kinetic energy (KE)


  KE = 1/2 mv^2
• The velocity of the object increases as it falls
• Since the velocity of the object is increasing, its kinetic energy is also increasing
• The increase in kinetic energy of the object is also due to the transformation of potential energy into kinetic energy
• Calculating kinetic energy


  1. KE = 1/2 mv^2

  2. Given: m = 1000 kg, v = 20 m/s

  3. Solution: KE = 1/2 (1000 kg)(20 m/s)^2

  4. KE = 200,000 J
• In performing calculations for kinetic energy, make sure that the unit of measurement of the mass is in kilograms (kg) and the unit of measurement of the velocity is in meters/second (m/s)
• The diagram shows an object with a mass of 60.0 kg located at a height of 6.0 m from the ground. The object moves from its initial position to point D
• Total Energy (TE)


  TE = PE + KE
• Potential Energy (PE)


  PE = mgh
• At the object's initial position: m = 60.0 kg, v = 0, h = 6.0 m, g = 9.8 m/s^2
• Calculating the object's potential energy at initial position

  1. PE = mgh

  2. PE = (60.0 kg)(9.8 m/s^2)(6.0 m)

  3. PE = 3528 J
• The potential energy of the object at maximum height is 3528 J
• The kinetic energy of the object at maximum height is zero
• The total energy possessed by the object is 3528 J
• Conservation of mechanical energy


  The sum of the potential energy and kinetic energy of an object is always the same regardless of the object's position
• If the potential energy of an object decreases

  Its total mechanical energy and kinetic energy increase
• If an object increases its velocity

  Its kinetic energy increases, while its potential energy decreases
• Real-life examples of conservation of mechanical energy

  • Kicking a ball
  • Biking downhill
  • Riding a swing