Harpo's World

comic book page about a contraption to make electricity with dog power.
Page 2

PERSIA: Harpo sees the pizza and starts running!

AKANE: This lowers the basket which pulls the rope and lifts the pizza out of the box.

PERSIA: The gears turn…

AKANE: …which generates electricity and turns on the light.

TEEGAN: I thought inventions were supposed to make things easier.

PERSIA: It's easy for us.

TEEGAN: How do you turn it off?

PERSIA AND AKANE: Hmmm—hadn't thought of that.

SQUIRREL (thinking): I don't think that will be a problem.


  • contraption: A mechanical device; a gadget.

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  1. How is chemical energy part of this machine?
    [anno: Chemical energy is part of this machine because the dog, in order to power its muscles, must convert food to chemical energy.]
  2. Describe two places in which the state of energy changes from potential energy to kinetic energy. Describe how the kinetic energy is released.
    [anno: Answers may vary but could include that when the weight is sitting on the board, the weight is in a state of potential energy. When the board is lowered, the weight enters a state of kinetic energy and falls downward. When the roller skate is at rest at one end of the board, it is in a state of potential energy. When the board is hit by the baseball, the roller skate enters a state of kinetic energy and moves across the board.]
  3. Think about whether or not this invention saves time or energy. Is this a good invention or a bad invention? Write a few sentences to explain your answer.
    [anno: Answers will vary but could include that this is not a good invention because there are extra parts to the contraption that are not necessary.]