Sg6 - Chapter 6 Study Guide for Energy 6.1 Isolated systems Skill 6.1 Understand qualitatively how an interaction between objects affects the in

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Unformatted text preview: Chapter 6 Study Guide for Energy 6.1 Isolated systems Skill 6.1 Understand qualitatively how an interaction between objects affects the in- teracting objects In beginning a problem, first define your system. Our choice of how to define the system is completely arbitrary. We want to choose our system so that it makes our problem easier to solve. This means that we only want to consider those things that have an effect on our problem. We can identify the things affecting our problem by looking at interactions. An interaction occurs when two objects affect each other such that both are accelerated. Interactions within a system are called internal interactions. Anything outside of our system is defined as the environment . Internal Example: (Defining two carts as the system) Assuming no friction with the ground or air, two carts collide causing the velocities of the carts to change (they were accelerated), thus, an interaction took place within the system. Interactions of a system with something in its environment are called external interactions. External Example: (Defining a ball as the system) Imagine throwing a ball. The ball starts out at rest and leaves your hand with some velocity. This acceleration is due to an interaction between you and the ball. Once the ball is released, there is an interaction between the earth and the ball (via the earth’s gravitational field) that causes it to accelerate toward the ground. The ball collides with air molecules which interact with the ball, slowing it down. Note: From the above example, we see that two objects don’t have to be in contact to interact. The hand and air touch the ball but the Earth does not. The Earth affects the ball by its gravitational field (we’ll learn the details about this in chapter 14). Skill 6.2 Be able to identify and construct isolated systems Depending on how we choose our system, as mentioned above, there may be internal interactions or external interactions. If we go back to the example with the thrown ball and choose the earth and ball to be our system, then the interaction between the earth and ball is internal to the system, and the interaction between the thrower and ball is between the system and its environment. If there are no external interactions (between system and environment), then it is called an isolated system . Essentially, the environment does not exist to an isolated system. The total linear momentum of an isolated system is always conserved. 6.2 Classification of collisions Skill 6.3 Be able to distinguish between elastic, inelastic, and totally inelastic collisions. 1 Although momentum is always conserved in isolated systems, the outcomes of collisions (another word for in- teractions) are not all the same. Just think of the difference between two billiard balls colliding and two cars colliding. We can classify collisions by comparing the difference in the two colliding objects’ velocities before the collision to the difference in velocities after the collision. We call this difference in velocity thecollision to the difference in velocities after the collision....
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This note was uploaded on 05/04/2008 for the course PHYS 2054 taught by Professor Stewart during the Spring '08 term at Arkansas.

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Sg6 - Chapter 6 Study Guide for Energy 6.1 Isolated systems Skill 6.1 Understand qualitatively how an interaction between objects affects the in

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