Buoyancy of Objects (Phase 4) Lifting Objects Flashcards
If you have an object and you wish to make it neutrally or positivley buoyant in water you need at least three of four following pieces of information.
What four pieces of information are there?
Weight of object above water (kg/pounds)
Weight of object underwater (kg/pounds)
Type of water immersed in (salt or fresh)
Amount of water displaced (L/cuft)
A 200kg engine is at the bottom of the sea, and the engine displaces 125litres of seawater.
What information needs to be caculated to lift it?
Weight of object above water = 200 kg
Weight of object underwater = ?
Type of water immersed = salt 1.03 kg
Amount of water displaced = 125 litres
A 200kg engine is at the bottom of the sea, and the engine displaces 125litres of sea water.
What is the upward force in water?
125litres (displaced) x 1.03kg (seawater)
= 128.75kg (upward force)
A 200kg engine is at the bottom of the sea, and the engine displaces 125litres of seawater, which makes the upward force displaced 128.75kg.
What is the weight of the engine in water?
200kg (weight out water) - 128.75kg (upward force)
= 71.25kg (weight in water)
A 200kg engine is at the bottom of the sea, and the engine weighs 72.25kgs in the water.
What totoal upward force would be needed to lift the engine with 50kg positive buoyancy?
72.25kg (weight in water) + 50kg (positive buoyancy)
= 121.25kg (total upward force)
A 200kg engine is at the bottom of the sea. It needs 121.25kgs of upward force to be positively buoyant on the surface.
How many litres need to be displaced in a liftbag to lift the engine to the surface?
121.25kg (upward force needed) ÷ 1.03 (seawater)
= 117.72litres (displaced to lift)
