3 min read•june 18, 2024
Krish Gupta
Daniella Garcia-Loos
Krish Gupta
Daniella Garcia-Loos
As we have introduced before, is the force caused by a difference in pressure at the top of the object and the bottom of the object.
Since pressure increases with depth, there is greater pressure pushing the object up then there is pushing it down. This net upward pushing force is called the buoyant force (also called the force of buoyancy). 🏄♂️
To find the strength of the buoyant force, we use Archimedes' Principle: the magnitude of the buoyant force is equivalent to the weight of the displaced fluid.🚣🏼♀️
Let’s try to understand this fundamental principle with an example. Say we have a bucket full of water, and we put a baseball in the water. Some of the water will spill out as the baseball takes up space. The weight of that spilled water is equivalent to the strength of the buoyant force on the baseball.
The buoyant force on the ball is simply the weight of water displaced by the ball:
Fb=Vboxρwaterg = (0.2m3)(1000kgm3)(10ms2)=2000N
The force of gravity on the ball is:
Fg = mg = 15kg(*10ms2) = 150N
These forces oppose each other, so we can say:
Fnet = Fb − Fg = 2000N − 150N = 1850N
** Archimedes used this fact to prove to a king that his crown was not made of gold (gold is very dense) and that he was actually being scammed by the jeweler. 👑 **
Here are some key points about buoyancy:
is another important quantity that you can be asked about on the AP exam. Apparent weight is the weight of an object in a particular fluid.
For example, try lifting your friend and sibling up in the air. The force you have to overcome is their entire weight. Now try to lift the same person in a pool. Isn’t it much easier? But why is that? Isn’t gravity still pulling with the same strength? It feels easier because the buoyant force is helping you push against gravity. 😝 Therefore, the apparent weight (Wa) of the object is the difference between its true weight (Fg) and the buoyant force (Fb) acting on it.
Here are some key points about apparent weight in a fluid: