What is energy exactly Energy is the capacity of a physical system to perform work A system is a portion of the universe chosen to see how varying conditions change it A system may be complex such as a human body or simple like a pinwheel spinning in the wind Work is a force acting on an object to move it It can be observed in one way or another but something must move to be part of work When you pick up a glass your hand and arm muscles are doing work When wind blows on a pinwheel its work makes the pinwheel spin I’m Not Playing I’m Working Though it can take effort to sit and listen to someone talking it’s not considered work unless something is moving something else Traveling in a car is not work since it’s the car’s engine that is turning the drive shaft not you But playing sports is considered work since that involves movement So next time someone says Get to work maybe it’s time to go out and have some fun 6
Energy Waiting to Happen Energy exists in two basic forms potential energy and kinetic energy Potential energy is stored energy It can be stored in large visible objects or inside atoms too small to see The most common potential energy works constantly on everything on Earth When you pick up your shoes you sense weight because gravity pulls on them They contain gravitational potential energy It comes from gravity’s effect on all objects on Earth It increases as the object gets farther from our planet’s core Work at Play When you swing on a swing you increase your gravitational potential energy by pumping your legs Building that potential energy takes work When you swing down you have to work to build up potential energy again 7
When you raise your shoes above your head you increase their potential energy You will hear the result of that stored energy if you drop them Objects with greater mass the amount of physical matter inside it are pulled more by gravity Raising a heavy rock a few inches off the ground is difficult but the increased gravitational potential energy makes it nearly impossible to raise above your head It’s the Climb Climbing steps also increases your potential energy The higher you climb the farther away from Earth’s core you go That’s why climbing many stairs is such hard work 8
Isaac Newton was born in Paris in 1642 He was very curious about Newton A New View of the World the way things worked Newton wanted to know why the moon orbited Earth and didn’t drift away He thought there must be some invisible power keeping the moon near Earth the same power that kept things on Earth from floating away He spent his life trying to understand the nature of the world such as why things fell down from trees or required more force to roll if they were larger Understanding Gravity Before Newton’s ideas about gravity were taken as fact scientists thought that anything moving at a constant speed must have a force acting on it They also believed that the force had to be touching the object directly This belief got in the way of understanding gravity which Newton later showed can affect celestial bodies such as planets a great distance away 9 Isaac Newton 1642 1727
