1. Logylogyat 13.Why bodies float Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

2. Logylogyat 13.1.Thrust 13.2. Pressure in Fluids 13.3. Pressure Exerted by a gas 13.4. Liquid Pressure 13.5. Buoyant Force 13.6. Archimedes’ Principle 13.7. Relative Density Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

3. Logylogyat THRUST 13.1.Activity 1)Press your thumb against a piece of paper Now press the pointed end of a pin against the same piece of paper. Do you notice any difference? Answer- When pressed, the pointed end of the pin presses easily through the piece of paper. That does not happen when we press the thumb against the piece of paper. Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

4. Logylogyat The force acting on an object perpendicular to the surface is called thrust. The thrust on a unit surface area is called pressure. Pressure= thrust/area SI unit of pressure is N/m 2. It is also called pascal in honour of the scientist Blaise Pascle Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

5. Logylogyat BLAISE PASCAL He was a French physicist and mathematician. He formulated pascal's law of pressure.He constructed mercury Barometer and measuring air pressure. Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

6. Logylogyat PRESSURE IN FLUIDS Activity  Take two rubber balloon.  Fill one with water and blow air into other.  Now prick both balloons with a pin.  What do you observe? Answer-Water and air both come out of the balloons. Air escapes quickly compared to water and produces a loud sound. Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

7. Logylogyat FLUIDS Liquids and gases are called fluids. Fluids exert pressure on the base and walls of the container that holds them, due to weight of fluid. Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

8. Logylogyat PRESSURE EXERTED BY GAS Activity  Take an empty can  Pour small quantity of water in it. Boil this water for a few minutes until the steam has driven out the air.  Now close the can with the stopper tightly.  Allow it to cool by pouring cold water over it.  What do you observe?  Answer- The can gets gradually crushed. Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

9. Logylogyat Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ? In the atmosphere, the force exerted on the unit surface area by the weight of the air column above it is called the atmospheric pressure. At the sea level it is about 10 5 N/m 2

10. Logylogyat THINK WHY? Some people feel their ears popping at the top of a mountain. Some people feel breathless as they climb higher and higher on a mountain. Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

11. Logylogyat LIQUID PRESSURE Pressure increases with the depth and is proportional to the density of the liquid. P d h Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

12. Logylogyat Buoyant force 1] Take a full bucket of water  Try to push inverted glass bottle into bucket.  What do you experienced?  Answer-we experienced that an upward force on the bottle due to the water in the bucket opposing the downward motion of the bottle. Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

13. Logylogyat The upward force exerted by a liquid(a fluid an general)on a body completely or partially immersed in it is called upthrust or buoyant. Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

14. Logylogyat ARCHIMEDES  C. 213 7 – 212 BC  Greek mathematician, physicist and engineer  First to calculate the ratio of a circle’s circumference to it’s diameter (π)  Calculated volumes of various shapes  Discovered the nature of the buoyant force  Inventor of many practical devices:  Catapults, levers, screws, etc. Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

15. Logylogyat ARCHIMEDES’ PRINCIPLE When a body is immersed partially in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

16. Logylogyat DENSITY & RELATIVE DENSITY Ratio of mass to volume is called density. Density = mass / volume SI unit is kg/m 3 and CGS UNIT is g/cm 3. Relative density = density of substance / density of water. It is also called specific gravity of a substance. It has no unit. Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

17. Logylogyat EXAMPLE Calculate pressure exerted by a screw on the wooden plank if area of contact of the screw is 0.5 mm 2 and its weight is 50 N. Given : Area = 0.5 mm 2 0.5 X 10 -6 m 2 weight of the screw = thrust = 50 N pressure = ? Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

18. 10 -6 Solution : pressure = thrust area = 50 0.5 x 10 -6 10 -6 = 100 x 10 -6 N/m 2 Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?

19. Logylogyat Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ? 2) A metal block having mass 10 kg with its length 50 cm, breadth 20 cm and heigth 10 cm. Calculate pressure exerted by metal block when it is mead to lie on a table top with surface – (a) ABCD (b) DCFE (c) BCFG. Solution : Thurst = Weight of metal block = mg = 10 X 9.8 = 98 N

20. Logylogyat Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ? (a)For surface ABCD, L = 50 cm, b = 20 cm Area = length X breadth = 50 cm X 20 cm = 1000 cm 2 = 0.1 m 2 Pressure = Thrust Area = 98 0.1 = 980 N/m 2

21. Logylogyat Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ? (b)For surface DCFE, l = 50 b = 10cm Area = length x breadth = 50 cm x 10 cm = 500 cm 2 = 0.05 m 2 pressure = = 98 = 1960 N/m 2 Thrust Area 0.05

22. Logylogyat Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ? (c) For surface BCFG, l = 20 cm b = 10cm Area = length x breadth = 20cm x 10cm = 200 cm 2 = 0.02 m 2 Pressure = = 98 = 4900 N/m 2 Thrust Area 0.02

23. Logylogyat EXAMPLE If density of water is 10 3 kg/m 3 and density of copper is 8.9 X 10 3 kg/m 3. Calculate relative density of copp? Given-Density of water-10 3 kg/m 3 density of copper-8.9X10 3 kg/ m 3 Relative density = Density of copper Density of water = 8.9X10 3 kg/m 3 10 3 kg/m 3 = 8.9 Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float

24. Logylogyat Rayat Shikshan Sanstha,Karmaveer Vidyaprabodhini,Madhya vibhag,Satara. Std-9 th Sub-Science &Technology Topic- Logylogyat Logylogyat Why Bodies float ?