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PHYSICS

PHYSICS. Applied Mechanics. liquid / gas. Pressure in a fluid. At sea level, pressure = p atm. h 1. p 1 = p atm + gh 1. pressure increases with depth. h 2. p 2 = p atm + gh 2. p = gh. x. container. Quick Check. p = gh. liquid.

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PHYSICS

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  1. PHYSICS Applied Mechanics

  2. liquid / gas Pressure in a fluid At sea level, pressure = patm h1 p1 = patm + gh1 pressure increases with depth h2 p2 = patm + gh2 p = gh

  3. x container Quick Check p = gh liquid Which graph shows how the pressure p varies with height x above the base of the container? A B C D p p p p x x x x

  4. x container Quick Check p = gh Liquid Liquid of twice density Which graph shows how the pressure p varies with height x above the base of the container? A B C D p p p p x x x x

  5. Upthrust At sea level, pressure = patm h1 low pressure p1 = patm + gh1 pressure increases with depth h2 p2 = patm + gh2 p = gh HIGH PRESSURE UPTHRUST

  6. Upthrust UPTHRUST

  7. Fish floats

  8. Calculate upthrust How to calculate the upthrust? UPTHRUST

  9. Upthrust = weight of fluid displaced weight of fluid displaced = upthrust

  10. Upthrust = weight of fluid displaced spring balance T = 9 N T = 6 N T = 5 N 9 N 9 N W = 9 N U = 3 N U = 4 N weighing machine

  11. Upthrust = weight of fluid displaced patm+ patm+ gh2

  12. Upthrust = weight of fluid displaced Quick Check 2

  13. Principle of flotation

  14. Principle of flotation

  15. Principle of flotation

  16. Principle of flotation When upthrust = weight, object floats

  17. Principle of flotation Object may float totally immersed

  18. Principle of flotation But what if the object is totally immersed and the upthrust is still less than the weight?

  19. Principle of flotation upthrust = weight When upthrust = weight, object floats

  20. Principle of flotation What if the object is pushed down underwater and let go … What will happen? upthrust > weight

  21. Principle of flotation

  22. Principle of flotation upthrust = weight When upthrust becomes equal to weight, object floats

  23. Principle of flotation Upthrust depends on how much volumeis immersed / displaced When upthrust = weight, object floats in equilibrium

  24. Three objects of equal volume are in equilibrium A Quick Check B C

  25. When object is not moving, the friction is called static friction. Friction When object is moving, the friction is called kinetic friction.

  26. Static Friction > Kinetic Friction

  27. Viscous force • When object is moving inside a fluid, it experiences viscous force • e.g. air resistance, water resistance water air As water is denser than air, object will hit more water molecules than air molecules, so water resistance > air resistance

  28. Viscous force increases with speed • The faster the object moving, • the greater the force in hitting the molecules, • the greater the resistance. water air

  29. v t Terminal Velocity (object falling in air) Object released from rest: v = 0 m s-1 a = g = 9.81 m s-2 mg Fv v = 3 m s-1 a = 4 m s-2 mg

  30. Terminal Velocity (object falling in air) Object released from rest: v = 0 m s-1 a = g = 9.81 m s-2 mg v Fv v = 3 m s-1 a = 4 m s-2 mg Fv t v = 4 m s-1 a = 2 m s-2 mg

  31. Terminal Velocity (object falling in air) Object released from rest: v = 0 m s-1 a = g = 9.81 m s-2 mg v Fv terminal velocity v = 3 m s-1 a = 4 m s-2 mg Fv t v = 4 m s-1 a = 2 m s-2 mg Fv v = 5 m s-1 a = 0 m s-2 mg

  32. Object released and falling in vacuum in air Quick Check After fallen distance x tair vair aair t0 v0 a0

  33. Falling vs moving up in air moving up in air falling in air Fv Fv v v mg mg viscous force opposite to weight viscous force and weight same direction  lesser accelerating force greater decelerating force

  34. Quick Check a = initial deceleration t = time to reach the top s = maximum height u u in air in vacuum object thrown up with same speed at same height

  35. Quick Check 3

  36. Projectile Motion u

  37. 50 m 50 m t = 1 s 50 m s-1 Projectile Motion When t = 1 s, sx = 50  1 = 50 m

  38. 50 m 50 m t = 1 s 50 m s-1 Projectile Motion sy = uyt + ½gt2 = 0 + ½g(1)2 = 5 m

  39. 50 m 50 m t = 2 s sx = uxt = 50  2 = 100 m sy = uyt + ½gt2 = 0 + ½g(2)2 = 20 m 50 m s-1 Projectile Motion

  40. 50 m 50 m t = 3 s sx = uxt = 50  3 = 150 m sy = uyt + ½gt2 = 0 + ½g(3)2 = 45 m 50 m s-1 Projectile Motion

  41. 50 m 50 m t = 4 s sx = uxt = 50  4 = 200 m sy = uyt + ½gt2 = 0 + ½g(4)2 = 80 m 50 m s-1 Projectile Motion

  42. 50 m 50 m t = 5 s sx = uxt = 50  5 = 250 m sy = uyt + ½gt2 = 0 + ½g(5)2 = 125 m 50 m s-1 Projectile Motion

  43. 50 m 50 m t = 6 s sx = uxt = 50  6 = 300 m sy = uyt + ½gt2 = 0 + ½g(6)2 = 180 m 50 m s-1 Projectile Motion

  44. 50 m 50 m 50 m s-1 Projectile Motion (with air resistance)

  45. Quick Check 4

  46. Quick Check 4

  47. Question to think about… Suppose You have some ice floating in a glass of water. When the ice melts, does the water level A rise B fall C stay the same

  48. Question to think about… Suppose you are on a boat floating in a lake. A large stone is on the boat. You take the stone and drop it into the water. Will the water level A rise B fall C stay the same

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