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Energy

  • Energy: the ability to cause change.
    • Measured in Joules (J)
      • 1 Joule = 1 kg*m2/s2
    • There are many different types of energy. We will start by learning about kinetic and potential.

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Kinetic Energy

  • Kinetic Energy: (KE) energy in motion.

KE = ½ mv2

    • Mass measured in (kg)
    • Velocity measured in (m/s)

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Example #1

A jogger with a mass of 60 kg is moving at a speed of 3.0 m/s. What is the jogger’s kinetic energy?

KE = ?

m = 60.0 kg

v = 3.0 m/s

KE = ½ mv2

KE = ½ (60.0)(3.0)2

KE = (30)(9)

KE = 270 J

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Practice Time

  1. A baseball with a mass of 0.15 kg is moving at a speed of 40 m/s. What is the baseball’s kinetic energy?

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  • If a stone has 390 J of energy and is moving with a speed of 12 m/s, what is the mass of the stone?

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  • What is the velocity of a 0.06 kg ball moving with 75 J of energy?

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Answer: KE = 120 J

Answer: m = 5.42 kg

Answer: v = 50 m/s

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Potential Energy

  • Potential Energy: stored energy
    • 3 types of potential energy:
      • Elastic potential energy
      • Chemical potential energy
      • Gravitational potential energy

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Potential Energy

  • Elastic Potential Energy: energy stored in objects being compressed or stretched
    • Examples:
      • Bow and arrow
      • Spring
      • Slingshot

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Potential Energy

  • Chemical Potential Energy: energy stored in chemical bonds of compounds.
    • Examples:
      • Firewood
      • Battery
      • Food

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Potential Energy

  • Gravitational Potential Energy: (GPE) energy stored in objects that are above Earth’s surface.

GPE = ham

    • Height measured in (m)
    • Acceleration due to gravity measured in (m/s2)
    • Mass measured in (kg)

At the peak of its path, the sphere pauses for just a second and has gravitational potential energy, before it converts back to kinetic energy as it moves towards the other spheres.

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Example #2

How much gravitational potential energy does a 5 kg rock have if it is sitting on the edge of a cliff that is 10 m high?

GPE = ?

m = 5 kg

a = 9.8 m/s2

h = 10 m

GPE = ham

GPE = ham

GPE = (10)(9.8)(5)

GPE = 490 J

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Practice Time

  1. A Viking ship roller coaster at the fair has a mass of 36,000 kg. If at its peak it reaches a height of 20 m off the ground, how much gravitational potential energy does it have?

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  • A 1.5 kg apple pie is sitting on the kitchen counter. If it has 13.44 J of gravitational potential energy, how tall is the counter it sits on?

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  • A suitcase weighing 120 N sits on a counter 1.8 m high in the airport. How much energy does it have?

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Answer: GPE = 7,056,000 J

Answer: h = 0.914 m

Answer: GPE = 216 J

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