This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: 1-1 REPRESENTING MOTION1Q1.1. Reason:(a)The basic idea of the particle model is that we will treat an object asifall its mass is concentrated into a single point. The size and shape of the object will not be considered. This is a reasonable approximation of reality if: (i) the distance traveled by the object is large in comparison to the size of the object, and (ii) rotations and internal motions are not significant features of the object’s motion. The particle model is important in that it allows us to simplifya problem. Complete reality—which would have to include the motion of every single atom in the object—is too complicated to analyze. By treating an object as a particle, we can focus on the most important aspects of its motion while neglecting minor and unobservable details. (b)The particle model is valid for understanding the motion of a satellite or a car traveling a large distance. (c) The particle model is not valid for understanding how a car engine operates, how a person walks, how a bird flies, or how water flows through a pipe. Assess:Models are representations of reality—not reality itself. As such they almost all make some simplifying assumptions. The test of a good model is the results it produces. The particle model allows us to model the motion of many objects simply and see common features of the movement of different objects. When used appropriately it is very useful. When used outside the range of its validity, it isn’t very helpful. Q1.2.Reason:The softball player starts with an initial velocity but as he slides he moves slower and slower until coming to rest at the base. The distance he travels in successive times will become smaller and smaller until he comes to a stop. See the figure below. Assess: Compare to Figure 1.10 in the text. Q1.3. Reason:Assess: The dots are equally spaced until the brakes are applied to the car. Equidistant dots indicate constant average speed. On braking, the dots get closer as the average speed decreases. Q1.4. Reason: As the ball drops from the tall building the ball will go faster and faster the farther it falls under the pull of gravity. The motion diagram should show the displacements for later times to be getting larger and larger. The successive displacements in the diagram given in the text get smaller and smaller. So the diagram given in the problem is incorrect. The correct diagram is on page 1-2. 1-2 Chapter 1Assess: Compare to Figure 1.5 in the text, which shows a motion diagram for two objects falling under the influence of gravity. The displacements increase during the fall of the object as we reasoned. Q1.5. Reason: Position refers to the location of an object at a given time relative to a coordinate system....
View Full Document
This note was uploaded on 11/30/2011 for the course PHYSICS 121 taught by Professor Shawhan during the Fall '10 term at Maryland.
- Fall '10