INTRODUCTION 2 DROPPING IN ou're standing on a skateboard about to drop into a half pipe You lean forward your skateboard's nose drops and you fly down the wall of the ramp You reach the bottom and begin gliding up the other wall Soon you're coasting back and forth riding the walls Have you ever wondered how a skateboarder speeds up and down a half pipe Or why sunlight feels warm Or why your body needs food It all has to do with energy Energy is what allows a skateboarder to continue moving up and down a pipe half
Sunlight is one of the most important kinds of energy Sunlight gives plants energy and supports life on Earth or the ability to do work Over the centuries scientists have wondered about energy They've formed theories and tested their ideas to come up with answers based on evidence This process is known as scientific inquiry Sometimes it took scientists years of research lots of experiments and even a few wrong ideas to answer their questions about energy First they noticed the energy of motion Then they discovered that there's energy in heat and sunlight Later scientists learned about the energy of electricity and fuel Through questions tests and theories scientists have discovered a lot about how energy powers our world 5
CHAPTER 1 WHERE DOES ENERGY GO kateboarding on a half pipe uses two kinds of energy At the top of the ramp a skateboarder has lots of potential energy meaning she is in a position where she can gain energy Once the skateboarder drops kinetic energy or the energy of motion is being used A skateboarder rocks between potential and kinetic energy while riding the walls of a half pipe EARLY ENERGY DISCOVERIES But how exactly does that work How is energy used and where does it go In the nineteenth century three Hermann von Helmholtz was one of the first scientists to write about the conservation of energy He came up with this idea while trying to understand how animals heat create
7 scientists were trying to figure out where potential energy goes Through their studies German scientists Hermann von Helmholtz and Julius Robert von Mayer and British scientist James Prescott Joule all concluded that energy is conserved it transfers from one form to another but is never destroyed That's what happens when a skateboarder flies up and down a half pipe The energy is never used up It simply changes from one form to another This idea became known as the conservation of energy However forces such as friction will eventually work against the skateboarder slowing the skateboard down and taking its energy away SKATEBOARDING ENERGY POINT A Potential energy is at its highest and kinetic energy is at its lowest POINT C Potential energy is at its highest and kinetic energy is at its lowest SCS POINT B Kinetic energy is at its highest and potential energy is at its lowest
