Buoyancy: AP Physics 2 Study Guide
Introduction
Hey there, future physicists! Ready to dive into the world of buoyancy? 🌊 Let’s float your boat (literally and figuratively) as we explore why some objects bob on the surface while others sink faster than your grades did after that one impossible pop quiz. Spoiler alert: this all boils down to some pretty nifty physics principles! Let's get started. 🚣🏼♀️
What is Buoyancy?
Buoyancy is that magical force that makes you feel lighter in a swimming pool and lets ships stay afloat without sinking like a stone. This force comes from the difference in pressure on the top and bottom of an object submerged in a fluid. Imagine you’re being squeezed upwards by a warm, cozy force that says, "Stay buoyant, my friend!" This net upward force is known as the buoyant force. 🏄♂️
Archimedes' Principle
To measure buoyant force, we turn to our old pal Archimedes. He figured out that the buoyant force on an object is equal to the weight of the fluid displaced by it. Got a baseball you’ve dunked into a bucket of water? The water that spills out is precisely the weight of the fluid giving the baseball its uplifting spirit.
Example Alert! 🚨
Say we have a box that weighs 15 kg and has a volume of 0.2 cubic meters. When we toss it into the water, here's what happens:

Buoyant Force (Fb): This force is the weight of the water displaced by the box.
[ Fb = V_{box} \times \rho_{water} \times g = (0.2 , \text{m}^3) \times (1000 ,\text{kg/m}^3) \times (10 , \text{m/s}^2) = 2000 , \text{N} ]

Gravitational Force (Fg): This force pulls the box down.
[ Fg = m \times g = 15 ,\text{kg} \times 10 ,\text{m/s}^2 = 150 , \text{N} ]

Net Force (Fnet): Compare the buoyant force and gravitational force to determine if the box floats or sinks.
[ Fnet = Fb  Fg = 2000 , \text{N}  150 , \text{N} = 1850 , \text{N} ]
So, the box will shoot up out of the water like a rocket! 🚀
Buoyancy Basics
Buoyancy can either make your boat float or your anchor sink, all depending on a few key factors. Let’s break it down:
 Buoyancy acts on objects submerged in a fluid, causing them to either float or sink. This force is ultimately dictated by the fluid displaced by the object.
 If the buoyant force is greater than the object's weight, up you go (like a ship)! If it's less, down you go (like that anchor).
Apparent Weight
Apparent weight is how heavy something feels when it's in a fluid. Imagine trying to lift your friend — not too hard on land, right? Now try lifting them in a pool. Easypeasy, lemonsqueezy! This is because the buoyant force works against gravity, making your friend seem lighter.
In pool terms, apparent weight (Wa) is your true weight (Fg) minus the buoyant force (Fb) giving you that underwater super strength.
Another Example: Apparent Weight
John tries lifting his 60 kg rock collection in and out of a lake.

On land, the real weight is:
[ Fg = 60 ,\text{kg} \times 10 ,\text{m/s}^2 = 600 , \text{N} ]

In water, if the displaced water equals 300 N, the buoyant force is:
[ Fb = 300 , \text{N} ]

So, in the lake, the rock feels:
[ Wa = Fg  Fb = 600 , \text{N}  300 , \text{N} = 300 , \text{N} ]
John is now a rocklifting champion of the lake! 🌊🏋️♂️
Key Terms
Apparent Weight: Weight perceived in a fluid, accounting for buoyant force. Simple math: real weight minus buoyant force.
Buoyancy: The uplifting force in fluids, caused by density and volume of displaced fluid.
Fun Fact
Archimedes reportedly discovered his principle while taking a bath and ran through the streets shouting "Eureka!" Talk about a groundbreaking bubble bath! 🛀🎉
Conclusion
And there you have it: the enchanting whimsy of buoyancy, where objects float, sink, or find a sweet balance in between. Just remember, science isn’t all serious — it can float your spirits just like buoyant forces can lift huge ships!
Now you’re all set to ace your AP Physics 2 exam and maybe even impress your friends with some buoyancy fun facts at the pool! 🏊♂️🚤
Good luck, and don’t let gravity get you down — unless buoyancy's got your back!