Directions: Read and highlight the following assignment. You have been taught how to properly highlight. Please use these skills in highlighting all new and important information. Different types of Energy Recall that energy can be broken down into two basic forms. Since energy is the ability to do work, we defined it using the term work. Energy can be thought of as both “work waiting to happen” and “work happening.” Work “waiting to happen” means that something might to do work. Work that is already happening is in motion. So, we have two kinds of work. Work waiting to happen and work in motion. Work in motion though uses something we have already been learning, speed. Recall, we said that speed deals with an object being in motion. So if we combine those two terms, we have an object in motion doing work. We refer to this as energy in motion or the science term, kinetic energy. Work Waiting to Happen In energy terms, the work waiting to happen is called potential energy. We define potential energy (PE) as the energy of position. In most of our examples the position refers to how high in the air something is. Although we don’t talk about these in 6th grade, there are many types of potential energy that explain, for example, how springs work or even how chemicals work. Gravitational Potential Energy The potential energy of position has a special name, gravitational potential energy. This type of potential energy depends on an objects weight and height. For example, when you lift a book into the air, this book will have potential energy. Potential energy is different from kinetic energy because it can be stationary or moving but kinetic energy has to be moving. For example, a book sitting on a shelf has lots of potential energy but has no kinetic energy. Calculating Gravitational Potential Energy The formula for calculating gravitational potential energy is as follows: PE = g x mass x height The “g” refers to the force of gravity pushing down on all of the objects on earth. Depending where you are in the solar system, the “g” value can change because gravity changes, but here on good old earth, gravity is approximately the same everywhere, 9.8. What about the height? Height above what? For example, if I am standing on a desk at school (breaking science classroom rules ☺), is my height in relation to the floor of the classroom or outside on the ground? Basically, it’s the closest point where you will stop falling. In my example, this would be the classroom floor. If I was jumping off the desk and out the window though, my height would be measured from top of the desk down to the ground. So understanding my “ground” location is extremely important for potential energy Let’s do an example. If I am standing on a desk 1 m off the floor and weigh 100 kg, what is my PE? PE = g x mass x height = 9.8 x 100 kg x 1m = 980 J Just as kinetic energy is measured in joules (J) so is potential energy. What if I was standing on the desk and jumping out the window (height is 21 m)? PE = g x mass x height = 9.8 x 100 kg x 21m = 20,580 J So just by increasing my height, the PE increases up to 20,580 J. Answer the following questions: 1.
Define potential energy 2.
What is the formula for potential energy? 3.
How are potential and kinetic energy different? 4.
How are potential and kinetic energy similar? 5.
Dominic is standing on a cliff watching the ocean. If he loses control of his cell phone and it slips out of his hand, how much potential energy would it have? The cell phone has a mass of 1.5 kg and is at a height of 40 meters. 6.
While cleaning out her gutters, Mrs. Meginnis falls off the ladder. If she has a mass of 45 kg and is 25 meters high, what is her potential energy? 7.
What would Mrs. Meginnis’ potential energy be once she hits the ground? Explain.