Terms & Stuff Pressure (P = F/A) Buoyancy Pascal’s Principle F.U.B.A.R.
The apparent loss of weight of a submerged object
What is buoyancy?
The upward force a liquid exerts opposite to gravity
What is buoyant force?
How does the weight of a floating object compare to the weight of the liquid it displaces?
Its weight is less
The idea that changes in pressure at any point in an enclosed liquid at rest are transmitted equally to all parts of the liquid
What is Pascal’s Principle? (P 1 = P 2 ) or (F 1 /A 1 = F 2 /A 2 )
In a piston, how does the ratio of the input and output areas compare to the distances they move?
They are inversely proportional
Some idiot takes a dare to do a belly-flop. If he falls with a force of 700 N, and 1.2 m 2 of his body hits the water, how much pressure does the water exert on him?
583 1 / 3 Pa
A pet store has a tall fish- tank for displaying their fish. The bottom is.2 m 2, and it feels 4850 Pa of pressure. How much does the water weigh in Newtons?
970 N
A bunch of kids are jumping on a trampoline. If their combined weight is 4000 N, and the trampoline feels / 3 Pa, how big is it?
15 m 2
You dive to the bottom of a 10 ft pool because you feel like it. If the weight density of water is 62.4 lb/ft 3, how much pressure do you feel? (Hint: P = ρd)
624 lb/ft 2
A kid throws a rock into a pond. It feels lb/ft 2 of pressure when it hits bottom, and the weight density of water is 62.4 lb/ft 3. How deep is the pond? (Hint: P = ρd)
58 ft
Explain why an iron ship floats.
It displaces a volume of water whose weight is great enough to support the ship
Why doesn’t the buoyant force act sideways?
The buoyant force depends on depth. The sides of an object are at the same depth, so the forces cancel out.
How does a submarine control its depth?
Basically, it changes its weight using its ballast tanks
Why might a big guy like Josh Williams have trouble floating?
His density would most likely be greater than water’s (muscle)
How does a fish change its depth?
It uses its swim bladder to change its volume
You push on one end of a water bed and increase the internal pressure to 200 Pa. How much pressure does the other end feel?
200 Pa
40 N 180 N 9 m 2 ? m 2
2 m 2
30 N 6 m 2 3 m 2 ? N
60 N
70 N 140 N 1 m ? m
.5 m
F 1 = 10 N F2 = 45 N A 1 = 2 m 2 A 2 = ? m 2 d 1 = 4 m d 2 = ? m
9 m 2 and 8/9 m
Which is lower in the water, a full or empty ship?
Full
The idea that an object is buoyed by a force equal to the weight of the water it displaces is known as…
Archimedes’ Principle
Give a real-life example of Pascal’s Principle in action.
You were probably right.
What is 1 Pa equivalent to?
1 N/m 2
How does the shape of a container affect the pressure in the liquid?
It doesn’t. Only depth affects pressure.