physics notes

Understanding Pressure And Atmospheric Pressure - Document Transcript

1. Problem/challenge/misconception: Atmospheric pressure is caused by the collision of air molecules on the surface Hands-On Activity to conceptualise atmospheric pressure. Topic: Understanding atmospheric pressure. Approach: Active Learning Method: Hands-On Activity Implementing strategy: a. Six activity stations are prepared around the laboratory. b. Students are divided into six groups to conduct the activities in rotation. c. Worksheet is provided at each station. d. Teacher discusses the results of the Hands-On Activity with the students. e. Teacher demonstrates an activity on the concept of atmospheric pressure followed by discussion. (Optional) Station 1: Spiderman Station 2: Breaking of metre rule using newspaper Station 3: Anti-gravity water Station 4: Shelled boiled egg in conical flask Station 5: Crumpled plastic mineral water Station 6: Drinking of carbonated beverage Demonstration: Crumpled tin can
2. Worksheet for Station 1 Apparatus: Suction pump (suction cap) Instruction: Press the suction cap onto a smooth surface. Questions: 1. What do you observe? 2. What happen to the air in the suction pump when you press it? 3. Compare the pressure between the air in the suction pump and the surrounding.
3. Worksheet for Station 2 Apparatus: Metre rule Material: Newspaper Instruction: 1. Spread a small sheet of newspaper on the table. 2. Place a half-metre rule underneath the newspaper with part of it jutting out as shown in the figure below. 3. Try to lift the newspaper by chopping the ruler at point A with your fist. 4. Repeat the activity with a bigger sheet of newspaper. Metre rule Newspaper A Questions: 1. Which sheet of newspaper is more difficult to lift? 2. Explain your answer.
4. Worksheet for Station 3 Apparatus: A drinking glass, a square shaped cardboard (5 cm x 5 cm) Material: Tap water. Instruction: 1. Fill in the glass to the brim with tap water. 2. Cover the glass with a cardboard. 3. Press the cardboard firmly and turn the glass upside down. 4. Release your hand from the cardboard when the glass is fully inverted. Question: 1. What happens to the water when the glass is fully inverted? 2. What causes the phenomenon that has been observed? 3. What happen if the same experiment is performed on the Moon?
5. Worksheet for Station 4 Apparatus: A conical flask Material: A shelled hard-boiled egg, boiling water Instruction: 1. Pour the boiling water into the conical flask to about half of its volume. 2. Place the egg at the mouth of the conical flask with about a third of the egg is inside the flask. 3. Shower the exterior of the conical flask with tap water. Questions: 1. What happens to the egg after a few minutes? (The egg slowly slides down into the conical flask) 2. Compare the air pressure inside the flask before and after the egg slides down the mouth of the conical flask? (The air pressure is higher before the egg slides down into the flask) 3. Why does the egg slide down into the conical flask? (Atmospheric pressure which is higher than the pressure inside the flask causes the boiled egg to be pushed into the flask) Extension: Will you observe the same situation if this experiment is carried out on the moon?
6. Worksheet for Station 5 Apparatus: 500 ml plastic water bottle Material: Hot water Instruction: 1. Pour about 200 ml of hot water into the plastic bottle and cap it. 2. Observe the plastic bottle after 1 or 2 minutes. 3. Compare the air pressure inside the plastic bottle and the surrounding. Questions: 1. What happens to the plastic bottle? 2. What causes the plastic bottle to be in the state you have observed? Extension: Will you observe the same situation if this experiment is carried out on the moon?
7. Worksheet for Station 6 Apparatus: Two drinking glasses, drinking straws Materials: Carbonated beverage Straw B Straw A Perforation Carbonated beverage Glass A Glass B Diagram 1 Instruction: 1. Set up the apparatus as shown in Diagram 1. 2. Using the drinking straws, try to drink the beverage in glass A and glass B. Question: 1. Which straw enables you to drink easily? 2. What will happen to the air column in drinking straw A when you drink from glass A? 3. Compare the air pressure inside straw A with the surrounding air pressure. 4. What will happen to the air column in drinking straw A when you drink from glass B? 5. Compare the air pressure inside straw B with the surrounding air pressure. Discussion: 1. Explain the causes of the phenomena that have been observed.
8. Effect of altitude on the magnitude of atmospheric pressure 1. Have you ever traveled using airplane or mountain climbing or being at the top of a tall building? 2. Do you experience any pain in your ear? 3. Teacher and students discuss the effect of altitude on the magnitude of atmospheric pressure using the diagram below. Atmospheric limit H1 H2 H3 A B C Sea level 4. Compare the air columns at position A, B and C (the sea level). Which air column is the longest? 5. Which position experienced highest atmospheric pressure? 6. What can you say of the relationship between the altitude and the magnitude of the atmospheric pressure ? Discussion: With the aid of the diagram below, teacher explains that the higher the altitude, the lower the air pressure.
9. Outer limit h2 Earth`s h1 atmosphere Earth
10. Topic: Understanding Gas Pressure Approach: Constructivism Method: Effective Questioning Technique Strategy: Teacher demonstrates Kit Model Theory Kinetic, followed by effective questioning technique to build understanding on the origin of gas pressure. Imagine that the polystyrene balls represent the air molecules trapped in an closed container as shown in the diagram below. polystyrene balls (a) What can you say about the number of polystyrene balls (air molecules) in the closed container ? (b) What can you say about the motion of the molecules? (c) State the type of collision between the molecules and the wall of the container.
11. +v -v m m Wall of container (d) What is the momentum of the air molecule before the collision? (e) What is the momentum of the air molecule after the collision? (f) What is the change in momentum? (g) If there are n molecules collide with the wall in t seconds. What is the total change of momentum in t seconds ? (i) (ii) What is the change of momentum in one second ? (ii) What is the rate of change of momentum ? (iv) What is the total impulsive force acting on the wall of the container ?