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# Forces in fluid

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It is the last Chapter of this semester in the physics Syllabus! Good Luck.

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### Forces in fluid

1. 1. Created by : Hamdy Karim Gr ade level ( s ): 8th grade Su bject area : Science Chapter 3 S ection 1 F orces in Fluids
2. 2. KS Standards and Activity Instructions Standards / Indicators : ( Use KS standards, not district standards. Include both number and standard description as well as indicator.) Gr ades 8-9 S TANDARD 2 : PHYSICAL SCIENCE- The student will apply process skills to develop an understanding of physical science including: properties, Rockets, Satellites, and Satellite Motion. B enchmark 3 : The student will investigate motion and forces. I ndicator 2 : Describes, measures, and represents data on a graph showing the motion of an object (position, direction of motion, speed). Ac tivity Instructions : S lide 3- Click on the numbered list 1-4 to open questions for discussion for the class related to the motion of the tennis ball in the background. Slide 4- Continue the class discussion, click on the hidden definition of &quot;motion&quot;, and see if the new definition changes the classes answer to the first question. Slide 5- Read slide 5 to the class. Slide 6- Read each blue card to the class. Have students hold up one finger if they think it is in motion, and two fingers if they don't think the situation is describing motion. Once the class is showing their answers have a student click on the box to reveal the answer. Slide 7- Introduce the vocabulary word &quot;reference point&quot;. Have students create a list of reference points they could use while sitting on a bus. Slide 8- Click on the numbered list to open questions for class discussion. Slide 9- Introduce the metric system. Pass out meter sticks for students to look at. Show them each of the measurement units identified on the stick. Give students practice using units by completing the &quot;Metric Inventory 2&quot; document attached. Slide 10- Go over speed formulas, emphasizing difference between constant and average speed. Practice calculating speed by completing &quot;Bubble Gum Physics&quot; handout attached.
3. 3. Outside, deep snow covers the ground. you put on your sneakers and head out. shovel in hand. when you step outside, your foot sinks deep into the snow. it's nearly up to your knees! not like the sparrow that hops across the surface of the snow without sinking! Forces in Fluid s &quot; Pressure &quot; Key Concepts * what does pressure depend on? * How do fluids exert pressure? * How does fluid pressure change with elevation and depth?
4. 4. · Why don't you sink into the snow when you wear snow shoes? Pr essure · Pressure is the force pushing on a surface.
5. 5. Why Don't you Sink? B ecause the size of the area over which the force is distributed has changed. · Pressure=Force/Area Pr essure is equal to the force exerted on a surface divided by the total area over which the force is exerted.
6. 6. Units for Pressure · Force is measured in Newton’s (N). · Area is measured in square meters. · SI unit for pressure is N/m2 which is also called the Pascal (Pa). ·1 Pa = 1N/m2
7. 7. Fluid Pressure · A fluid is a substance that can easily flow. · Fluids exert pressures on surfaces they touch.
8. 8. Fluids are made of molecules. · Molecules are constantly moving. · All of the forces exerted by the individual molecules in a fluid add together to make up the pressure exerted by the fluid.
9. 9. Fluid pressure = Total force exerted by the fluid divided by the area over which the force is exerted.
10. 10. Fluid Pressure all around . · Air Pressure or atmospheric pressure : is the pressure exerted on us by the air.
11. 11. How can we support the weight of the atmosphere? · Each cubic meter of air has a mass of 1 kg. · How can we support this and not feel a thing? · Because in a fluid that is not moving, pressure at a given point is exerted equally in all directions.
12. 12. Balanced Pressures As the atmosphere is pushing down on your hand – there is also atmospheric pressure pushing up on our hand.
13. 13. Variations in fluid pressure · Air pressure decreases as elevation increases. Remember air pressure at a certain point results from the weight of air above that point.The higher you go the less weight above you.
14. 15. Why do your ears pop? · As the air pressure outside your body adjusts the air pressure inside your body has to adjust too. Th e pressure inside is greater than outside so pressure is released and all is balanced again.
15. 16. Pressure and depth · Pressure increases as you descend – because there is more water above you and therefore more weight above you.
16. 17. Measuring Pressure T here are two basic instruments used to measure air pressure: the mercury barometer and the aneroid barometer . The mercury barometer is a simple tube that has been inverted into a container filled with mercury. The air pressure pushes the mercury up the tube a given height, which can be measured. Other liquids, such as water, can also be used. An aneroid barometer contains no liquid, but small cells that expand and contract with the changes in air pressure. By attaching a needle to the cells, the air pressure can be measured.