The Incredible Hull: Slip Sliding Away

Transcription

1 Title: The Incredible Hull: Slip Sliding Away (Friction & Motion) Grade Level (s): 7-8 Introduction:Our common experience is that objects in motion do not often stay in motion. In real life when we move or try to move one object against another, there are interactions or forces that resist that motion. Friction force is the force that opposes the motion or the tendency of motion between surfaces in contact. The mechanism that retards the motion is called friction. When friction opposes a motion in progress it is called dynamic or kinetic friction. When friction prevents a motion from occurring, it is called static friction. Friction is present in all states of matter whether solid, liquid or gaseous. The study of forces and motions in fluids is called fluid mechanics. When examining vessel hull design, not only is the shape of the hull important, so is the surface texture of the hull. Friction between solids and liquids depends upon more factors than just the shape of the solid immersed in that fluid. Dynamic friction between solids depends on the normal force on the object and the materials of the surfaces in contact as well as the texture of the surfaces. This lesson plan will examine how friction affects vessel hull design. Learner Objectives: The student will be able to understand the concept that friction between solids and liquids depends upon both the shape and surface texture of the solids (the hull) moving through fluids (i.e. the ocean). The student will be able to understand that friction depends upon the materials in which contact occurs. The student will be able to understand that friction usually takes away energy in motion changing it into heat. Sunshine State Standards: Science: SC.C.1.3.1, SC.C.2.3.3, SC.C.2.3.3, Math: MA.E.1.3.1, MA.D Competency-Based Curriculum: Science:.M/J-I-8-A, Math: M/J-I-V-2-A, M/J-3-IV-6-A III-A-17

2 Materials: Paper White glue Water Large plastic containers Pencils Varnish Sand Rubber band Paintbrush Paint thinner Sandpaper Activity Procedures: 1. Have a small group of selected students stand and run in place. Brainstorm as to why students were able to walk and run introducing the concept of friction. 2. Have the students rub one hand against the other introducing friction as a force that changes energy in motion to heat. 3. Define and explain the following terms: solid, liquid, gas, hull, friction, dynamic or kinetic friction, static friction, and fluid dynamics. 4. Access prior knowledge by introducing and discussing how cars and bicycles are aerodynamically designed. Begin discussion on how boats hulls are shaped. Contrast white water kayaks (flat, smooth hulls to maximize slide and minimize direction) and canoes (straight, deep v hulls to minimize slide and maximize direction). Discuss various hull shapes. 5. Place students in cooperative learning groups and have each group design, build and draw their own hull designs using paper mace. 6. Introduce the concept of fluid dynamics and water repellent polymer coatings (FCAT supplemental with corresponding content have been included at the conclusion of this lesson plan.) 7. Using one regular pencil and one altered pencil (coated with varnish mixed with coarse sand particles), teacher will demonstrate the pencil coated with sand will encounter more friction and its velocity will decrease. A modified sling shot and long plastic container filled with water will be used to race the two pencils. Students can then be given similar containers (without the lauching device) and pencils to verify that the smooth surface pencils encounter less friction. III-A-18

3 Student Assessment: Teacher will monitor student participation in brainstorming activity (1), boat hull paper mace (4) construction and pencil-hull friction lab (6). Teacher will prepare critical thinking skills questions for the students during the lab and discussion activities. Activity Extensions: 1. Have students calculate the coefficient of dynamic friction for textbook moving on two desks: one smooth wooden desk and another where sandpaper covers the desk. The formula for dynamic friction is as follows: F stands for friction, m stands for coefficient of friction and N stands for the normal force: F = mn Wooden Desk: F= 6 Newtons N=20 NewtonsAnswer: m=0.3 Wooden Desk coated with sandpaper F= 18 NewtonsN= 20 Newtons Answer: m=0.9 (Math) 2. Have the students write an essasy about Christopher Columbus voyage to the new world. (Language Arts and History) Friction Exercise Sheet: 1. What is friction? Answer: Friction is a force that always opposes the motion between two surfaces in contact. 2. Is friction only present in solids? Answer: No, friction is present in any state of matter. 3. How can we reduce friction between solids and liquids? Answers may vary. By changing the shape of the solid, by putting some repellent material on the solid object. III-A-19

4 Home Learning Activity: Have the students research hull designs on the Internet and/or provide handouts on hull design prior to activity number four.. Vocabulary: solid, liquid, gas, hull friction, dynamic friction, kinetic friction, static friction, fluid dynamics References/Related Links: American Red Cross (1997). Start sailing right. Portsmith, RI: United States Sailing Association III-A-20

5 The Incredible Hull: Slip Sliding Away Reading Passage # 1 One of the greatest enemies of an Olympic swimmer is friction. The friction between a swimmer s body and the water causes drag. This is why swimmers shave all the hair from their bodies to make their skin as smooth as possible to reduce the amount of drag. This year, sporting goods manufacturers introduced a new bodysuit to the public. This bodysuit worn by swimmers reduced drag because of the special sleek materials used to make them. Various athletes wore this special technologically advanced clothing during the 2000 Summer Olympic Games in Sydney, Australia. The bodysuits are made from polymers and other materials to make them ultra-sleek and smooth. They cover the entire body so that the water flows against the material instead of the skin of the swimmer. This is quite a change from previous swimming outfits which covered very little of the swimmer s skin. III-A-21

6 Swimming Can Be a Drag FCAT Questions Directions: Read the passage, then answer all the questions below. Answer multiple-choice questions by circling the letter of the answer that you select. Write your answer to the Read, Think, and Explain question on the lines provided. 1. Why do swimmers shave all the hair from their bodies? 2. Define the force of friction. 3. How can swimmers reduce drag? 4. How can friction be reduced between solids? III-A-22

7 How to Reduce Friction Between Water and the Hull of a Ship Reading Passage #2 A major Japanese ship maker has developed a new, highly water-repellent material. When applied to the hull of a boat, this material reduces by half the friction between the boat and the water, leading to a 20% to 30% increase in fuel efficiency. Like water off a duck s back, the material which can be sprayed onto a surface, is composed mainly of fine particles of silica (silicon dioxide) that are chemically engineered to repel water. The water repellency of the material is so high that when an object to which it has been applied is placed in water, a thin (2 to 3 mm) layer of air forms between the object and water. The ship maker calculates that friction between the hull of a standard freighter and the water provides approximately 60% of the resistance faced by the ship as it sails. If this friction, the greatest source of resistance to the boat, is halved, the overall resistance will drop by approximately 30%, resulting in a matching jump in fuel efficiency. On the other hand, skin friction and form drag contribute to overall vehicle drag. Friction drag varies with speed and the exposed surface area so smaller hulls with less surface area have less friction drag. Form drag is a function of how well the hull shape minimized flow separation. Longer, more slender shapes tend to perform better in this aspect. III-A-23

8 How to Reduce Friction Between Water and the Hull of a Ship FCAT Questions Directions: Read the passage, then answer all the questions below. Answer multiple-choice questions by circling the letter of the answer that you select. Write your answer to the Read, Think, and Explain question on the lines provided. 1. Friction between the hull of a ship and water can be reduced by: A. Increasing the velocity. B. Increasing the weight of the ship. C. Putting some water repellent material on the hull of the ship. D. Making the ship lighter. Answer: C 2. Another way of reducing the drag force between the water and the ship is by: A. Increasing the velocity. B. Decreasing the velocity. C. Increasing the contact area with the water. D. Decreasing the contact area with the water. Answer: D 3. By reducing the drag force: A. The boat loses efficiency. B. Barnacles don t grow as fast. C. The boat s efficiency increases. D. The boat will consume more fuel. Answer: C 4. Why are the bows of boats usually pointed? A. To prevent the hull from breaking. B. To improve the boat s ability to float. C. To cut through the water and reduce the drag force. D. None of the above. Answer: C III-A-24

9 5. Part of the energy the boat loses while moving is due to: A. Energy of motion. B. Sound C. Fuel loss. D. Heat Answer: D 6. When you drop two objects of the same mass and material, but different shapes into water, they won t reach the bottom at the same time because: A. They have different initial velocities. B. The drag force in different due to their shapes. C. Gravity is different for the two objects. D. They might have different density. Answer: B III-A-25