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Buoyancy and Pressure

Buoyancy and Pressure. Force: Weight: Buoyancy Archimedes Principle Pressure Formulas and Atmosphere. Will an Object Float?. Buoyancy vs Weight. Aluminum: D = 2.7g/cm 3. Play Dough Boat: Will it float?. Force: a push or a pull (unit: Newton).

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Buoyancy and Pressure

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  1. Buoyancy and Pressure Force: Weight: Buoyancy Archimedes Principle Pressure Formulas and Atmosphere

  2. Will an Object Float? Buoyancy vs Weight

  3. Aluminum: D = 2.7g/cm3

  4. Play Dough Boat: Will it float?

  5. Force: a push or a pull (unit: Newton)

  6. If Force is balanced an object will not move!

  7. Buoyant Force is Real

  8. Buoyant Force is Real: Will a Basketball fly in the air on its own?

  9. Have you ever lifted up a friend in the water? • Are they lighter or heavier?

  10. Buoyant Force (FB) Weight (FW)

  11. Weight =mg • Weight is equal to the mass of an object times the acceleration due to gravity on the surface of earth. • Weight is a force so the unit is Newton. • Mass is measured in kilograms (kg) • g is a constant: 9.8m/s2

  12. Sample Weight Problems: • An object has a mass of 35 kilograms. What is its weight? • A car has a mass of 2000kg (kilograms). What is its weight? • A pencil has a mass of 0.030kg. What is its weight?

  13. Buoyant Force • Buoyant Force : anupward force exerted by a fluid on an object placed in that fluid. • In English this means when you get in water, the water is actually pushing you upwards.

  14. Archimedes • Archimedes Principle: Buoyant force is equal to theweight of the fluid displaced . • However much water an object pushes out of the way, if you were to get the weight of that water, that would equal the upward push of the water (buoyant force)

  15. Buoyant Force (FB) According to Archimedes's Principle: FB = mh20g (unit: Newtons) • mass of fluid displaced in kilograms • g is still 9.8m/s2

  16. Overflow Can / Spring Scale Activity • Put pennies in a small foil boat in an overflow can. • Put a large and mall mass in. • Put in a piece of foil, unfold it into a boat and keep adding pennies.

  17. A person feels • A person feels lighter in water when you pick them up because the buoyant force is helping you. • On land its you versus their weight. • In water its you and the buoyant upward force versus their weight.

  18. Sinking & Floating • If Weight > Buoyant Force the object sinks • If Buoyant Force > Weight the object rises • When Buoyant Force = Weight the object floats/suspends.

  19. Which is greater: the Weight or Buoyant Force?

  20. Why will an Iron ship float? • A solid iron block will always sink but shaping Iron into a hollow form increases the volume it occupies, reducing the overall density. • In other words: iron is denser than water but water is denser than a hollow ship made of iron that is filled with air. • The more water you displace, the greater the upward buoyant force.

  21. Iron ships will Float but since Iron is denser than water, if the ship gets hole in it and floods, it will definitely sink….

  22. Aluminum Foil and CONCRETE BOATS!

  23. CONCRETE BOATS

  24. Aluminum Foil Boat

  25. How do Submarines Work?

  26. Problem 1 • An object has a mass of 2kg and it has a total volume that will displace 1.8kg of water if totally submerged in water. Will this object sink or float in water?

  27. Problem 1 Solution List what you know: Solve the Problem FB = mH20g 1.8kg · 9.8m/s2 = 17.6N FW = mg 2kg · 9.8m/s2 = 19.6N FW (19.6N) > FB (17.6N) The Object Sinks • FB = mH20g • FW = mg • m = 2kg • mH20 = 1.8kg • g = 9.8m/s2

  28. Problem 2 • An object has a mass of 1kg and will displace 3kg of water if totally submerged. Will this object sink or float in water?

  29. Problem 2 Solution List what you know: Solve the Problem FB = mH20g 3kg · 9.8m/s2 = 29.4N FW = mg 1kg · 9.8m/s2 = 9.8N FB (29.4N) > FW (9.8N) The Object Will Float or Rise • FB = mH20g • FW = mg • m = 1kg • mH20 = 3kg • g = 9.8m/s2

  30. Problem 2b • An object has a mass of 27kg and will displace 35kg of water if totally submerged. Will this object sink or float in water? Calculate the weight and buoyant forces acting on it.

  31. Problem 2c • An object has a mass of 42kg and will displace 42kg of water if totally submerged. What will happen to this object if submerged? Calculate the weight and buoyant forces acting on it.

  32. Problem 3 Solution List what you know: What do I need to know? mH20 = ???? You can try calculating density since you know the mass and volume of the object: D = 3kg/ 0.06m3 = 50kg/m3 Density of Water = 1000kg/m3 This SOLID object will float • FB = mH20g • FW = mg • m = 3kg • v = 0.06m3 • g = 9.8m/s2

  33. CAUTION • Objects with a density greater than that of water can still float if they are made to displace a lot of water. • For example, many ships are made out of iron which is denser than water but they can float very well and carry heavy loads.

  34. Buoyant Force (FB) Weight (FW)

  35. Mass vsWeight ppt.

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