3.1 Understanding Pressure


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3.1 Understanding Pressure

  1. 1. Problem/misconception/challenge faced by the students 1. Problem: Students are not able to distinguish between force and pressure. 2. Misconception: Bigger force always associates with bigger pressure. Construction of concept through effective questioning Topic: Understanding Pressure. Approach: Constructivism Method: Effective Questioning Technique. Strategy: Perform a simple activity followed by effective questioning technique to build the concept of pressure. Suggested Activity: Students are asked to press both ends of a pencil with equal force. 1. What is pressure? (Accept any answer) Suggested activity: Students are asked to press both ends of a pencil with equal force. 2. Which end causes more pain to your finger? (Sharp end) 3. Why? (Sharp end has smaller surface area) 4. What is the relationship between the surface area and the pain experienced by your finger? (Smaller surface area, more pain) Note: Student associates pain with pressure. More pain means more pressure exerted on the finger.
  2. 2. 5. Which end exerts bigger pressure? (Sharp end) 6. What is the relationship between the pressure and surface area? (The smaller the surface area, the bigger the pressure) 7. What will you feel if you press both ends with a bigger force? 8. What is the relationship between the force and the pressure? (The bigger the force, the bigger the pressure)
  3. 3. Date: SUBJECT: PHYSICS YEAR: FORM 4 LEARNING AREA: 3. FORCES AND PRESSURE LEARNING OBJECTIVE: 3.1 UNDERSTANDING PRESSURE LEARNING OUTCOMES: Students should be able to: F 1. conceptualise and define pressure as P = . A 2. solve quantitative problems involving pressure. 3. describe applications of pressure. Time: 2 periods (80 minutes) Subject Content: Pressure Suggested Activities: 1. Students are asked to press both ends of a pen with equal force. 2. Questions will be verbally posed in logical sequence so that students can construct the concept of pressure. F 3. Discuss the definition of pressure as P = based on the concept built in Activity 2 A 4. Teacher discusses some examples of quantitative problem-solving involving pressure. 5. Students discuss in group to get some ideas regarding applications of pressure in daily life.
  4. 4. Moral Values: Being cooperative Creative and Critical Thinking Skills: Relating, making generalisation, conceptualisation & problem-solving. Teaching Aid: Computer and LCD projector. STAGES / RESOURSES / CONTENT SUGGESTED ACTIVITIES STEPS REMARKS Set Induction 1. State the learning outcome from the teaching courseware. Computer and LCD (10 minutes) 2. Use simple demonstration by asking a student to walk on a projector sand pit using her school shoes. The same student then A pair of high heel shoes walks on the sand pit again by putting on a pair of high and a tray of sand or sand heel shoes. pit 3. Students make observation. 4. Teacher poses these questions: (a) Which pair of shoes produce a deeper footprint on the sand pit? (b) Why do you think so? (Accept any answer) Development
  5. 5. (70 minutes) STEP 1 Conceptualise 1. Students are asked to press both ends of a pen with equal Pen (20 minutes) and define force. pressure as 2. Teacher poses the following questions verbally to the class To build concept of to build understanding of pressure through constructivism. pressure increases when F P= A (a) What is pressure? (Accept any answer) the surface area in contact (b) Which end causes more pain to your finger? decreases. (Sharp end) (c) Why do you think so? (d) Which end has smaller surface area? (e) What happens to the pain you experienced when the surface area in contact is smaller? (f) Which end exerts a greater pressure on your finger? (g) What happens to the pressure exerted on your finger when the surface area in contact is smaller? (h) Can you state the relationship between the surface area and the pressure? 3. Students are asked to press both ends of the pen with Students construct idea
  6. 6. a greater force. The following questions are then posed that pressure increases verbally to the class or to individual students. with force. (a) What do you feel when a greater force is exerted? (b) What can you say of the pressure exerted on your finger when the force increases? (c) What relationship do you think exists between pressure and force? 4. Teacher leads students to conceptualise pressure which is Deducing the directly proportional to the force (F) and inversely proportional mathematical relationship to the surface area (A) based on the experience and between Pressure (P), discussion through a series of questions as the above. Force (F), and Surface Area in contact (A). 5. Conclude this part of the lesson by stating that pressure is F defined as force per unit area, i.e P = and its SI unit is A Nm-2 or Pascal (Pa).
  7. 7. STEP 2 Problem solving 1. Teacher and students discuss a few examples of (30 minutes) quantitative problems involving pressure. (Refer to Appendix 1 ) ( 10 minutes ) 2. Students try Mastery Practice 3.1 - Q1 & Q2 (Text Book) to reinforce understanding of the concept. ( 15 minutes ) 3. Students are encouraged to look for extra exercises involving pressure from reference books or past years examination papers. STEP 3 Applications of 1. Teacher and students discuss the applications of pressure (15 minutes) pressure in daily life. Examples : • The blade of a knife has a very small area that exerts such a high pressure that the meat can be cut easily. • The sharp tip of a thumbtack has a very small area in contact with the board. Hence the tip can pierce through the board due to the high pressure it exerts.
  8. 8. • You will not sink into the snow if you are wearing skis. The pressure exerted is low due to the large surface area of the skis. • The large tracks of a bulldozer help to reduce pressure so that the heavy bulldozer will not sink into the soft ground. 2. Students are encouraged to participate in the classroom discussion and share their own experiences in daily life that involve application of pressure. Closure 1. Evaluation of understanding of pressure using teaching Computer & LCD projector courseware. (10 minutes) 2. Show the conclusion of what the students have learnt from this topic from the teaching courseware. . Appendix 1 1. The diagram below shows the dimension and the weight of a wooden block resting on the floor. Calculate
  9. 9. (i) the maximum pressure exerted, and (ii) the minimum pressure exerted. Weight = 24 N 4m 2m 3m 2. A student is pressing a thumbtack into a notice board with a force of 15 N. The area of the head and the tip of the thumbtack is 0.0001 m2 and 1×10-6 m2 respectively. (i) Calculate the pressure exerted on the student’s thumb. (ii) Calculate the pressure exerted by the thumbtack onto the notice board. (iii) What causes the difference in pressures calculated in 2(i) and 2(ii)? Summative Test
  10. 10. F 1. Pressure is defined mathematically as P = , where F is the force and A is the surface area in contact. What is the SI unit for A pressure? 2. Explain how the webbed feet of a duck helps it to move around more easily on the muddy ground. 3. A four legged table of 200 N has a total cross sectional area of 40 cm2. What is the average pressure exerted by each leg of the table to the floor? 4. What is the minimum pressure exerted by the block onto the floor in the diagram below. 1.2 m 0.4 m 0.6 m 5. List down four examples of the applications of pressure in our daily life.