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**Kinetic and Potential Energy**

Today we are going to learn about Kinetic and Potential energy.

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After the Lesson: You will be able to define and identify Kinetic and Potential energy. You will be able to give examples of the two forms of energy. You will be able to explain how one can transfer to the other. In this lesson, students will learn the definitions of both potential and kinetic energy. They will also be able to give examples of each and explain how potential energy changes into kinetic energy.

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**The ability or capacity to do work.**

Definition of Energy… The ability or capacity to do work. Measured by the capability of doing work: potential energy or the conversion of this capability to motion: kinetic energy. In order to understand the different forms of energy, you have to know what the term “energy” means. Energy is the ability or the capacity of an object to do work. This is measured in two different ways : capability of doing work- known as potential energy, and the conversion of the capability to motion- called kinetic energy.

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Types of Energy Kinetic Energy Potential Energy

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**Forms of Energy Chemical Sound Radiant Electrical Mechanical Magnetic**

Thermal Nuclear

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**Potential Energy… Energy due to position or stored energy.**

The first form of energy is Potential energy. This is energy due to position.. Its also known as “stored energy.” To calculate PE you take the object’s weight and multiply it by the earths gravitational pull and the distance the object can fall. Potential energy is calculated by: The object’s weight, multiplied by the earth's gravitational pull (9.8 m/sec sq), multiplied by the distance the object can fall.

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POTENTIAL ENERGY Potential energy exists whenever an object which has mass has a position within a force field. The most everyday example of this is the position of objects in the earth's gravitational field. The potential energy of an object in this case is given by the relation: PE = mgh PE = Energy (in Joules) m = mass (in kilograms) g = gravitational acceleration of the earth (9.8 m/sec2) h = height above earth's surface (in meters)

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**Examples of Potential Energy:**

Stretching a rubber band.. -Stores energy Water at the top of a waterfall.. -Stores energy Yo–Yo in held in your hand.. -Stores energy because of position Some examples of potential energy are.. Stretching a rubber band… this store energy because it has the ability of doing work. Water at the stop of the fall has the ability of falling, therefore it stores energy. A Yo Yo held in your hand stores energy because when you alter its position it now has the ability of doing work. A bow and arrow has stored energy because its position has changed and it now has the capability of shooting the arrow. Drawing a Bow… -Stores energy because of position

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**When the position of an object is altered it, creates Potential Energy.**

A yo-yo on the table, doesn’t have energy, but when picked up, it alters its position and now it has the ability (or potential) to do work. A bow doesn’t have the capacity to do work, unless it’s held at an elevated position. Almost every object has the potential to do work, or store energy, but the objects original position needs to be altered so it can eventually move. For example: If the Yo-Yo we used in example one was just sitting of a table, it doesn’t have potential energy because the object by itself doesn’t have the capability to do work or move. If you pick the Yo-Yo up off the table, it now has altered its original position, and can store energy because it can now work with your help.

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**Definition of Kinetic Energy…**

The energy of motion. The second form of energy is Kinetic energy. As we just mentioned is the previous slide, kinetic energy is the energy of motion. This is calculated by ½ of the object’s mass multiplied by double the object’s speed. Kinetic energy is calculated by one half of the object’s mass, multiplied by the object’s speed- squared.

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KINETIC ENERGY The greater the mass or velocity of a moving object, the more kinetic energy it has. Kinetic Energy Lab

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**Examples of Kinetic Energy…**

Shooting a rubber band. Water falling over the fall. A Yo-Yo in motion. Releasing the arrow from the bow. Using the same examples as potential energy, you can see how the same object that previously had PE now has KE. If the rubber band we were stretching to give it PE, were to be let go, it would now have KE because its now in motion. Same with the water in the waterfall, when it falls over, its now in motion. The Yo-Yo and the arrow from the bow are also moving, giving all these objects KE.

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**Potential Energy Converted to Kinetic Energy…**

When stored energy begins to move, the object now transfers from potential energy into kinetic energy. Potential energy eventually will need to transfer from it’s stored energy into motion. If a person is standing still, they obtain potential energy because the have the ability to walk or run… if the same person who is standing still decides to start running, then they have transferred their PE into KE… in other words, they went from storing energy, to moving energy. Standing still Running

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**What happens when the cord is cut?**

Potential energy is converted to kinetic energy!

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Potential Energy- “stored” energy related to an object’s height above the ground the higher something is, the more potential energy it has Kinetic Energy- “energy of motion” related to an object’s velocity the faster something is traveling, the more kinetic energy it has

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**Click on your answer to see if you are correct.**

Directions Decide whether each slide is an example of potential or kinetic energy. Click on your answer to see if you are correct. Whenever you see this picture, you will need to write the answer in your journal.

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**Kinetic Energy Potential Energy**

The Ball Kinetic Energy Potential Energy

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**Kinetic Energy Potential Energy**

The Ball Kinetic Energy Potential Energy

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Potential Energy Kinetic Energy

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Potential Energy Kinetic Energy

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Kinetic Energy Potential Energy

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Kinetic Energy Potential Energy

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Potential Energy Kinetic Energy

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Potential Energy Kinetic Energy

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Kinetic Energy Potential Energy

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Kinetic Energy Potential Energy

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Conservation of energy says that the amount of energy the coaster has will always be constant. This means the potential energy of the car plus the kinetic energy of the car must always be the same. If the potential goes up, the kinetic must come down; if the kinetic goes up, the potential must come down.

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**The Hill: Conservation of Energy**

Why is the first hill of the roller coaster always the highest?

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**At the top of the first hill:**

Kinetic Energy? The coaster’s velocity is zero . . . Kinetic energy = 0 Potential Energy? The coaster is very high . . . Potential energy = high All of the coaster’s energy is in the form of potential energy.

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**At the bottom of the hill:**

Kinetic Energy? The coaster is moving at a high velocity. Kinetic energy = high Potential Energy? The height of the coaster is zero . . . Potential energy = 0 By the time the coaster reaches the bottom of the hill, all potential energy has been transformed to kinetic energy.

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**But why is the first hill highest?**

When the coaster reaches the bottom of the first hill, all its energy has been transformed from potential to kinetic energy. As it goes up the next hill, that kinetic energy must be transformed back into potential energy so the process can repeat. But don’t forget friction – the coaster is always losing energy to friction between the car and the tracks, so each time it goes up a hill it will have less kinetic energy to transform back into potential.

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The first hill of a roller coaster always must be the highest, otherwise the coaster won’t have enough energy to get up the other hills.

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