Hydrostatics:change in weight of a system if a foreign body is introduced

AI Thread Summary
Introducing a foreign body, such as a bob, into a beaker of liquid alters the total weight of the system based on whether the bob floats or sinks. When the bob floats, the forces are balanced, and the total weight of the system becomes the weight of the liquid plus the weight of the bob. In contrast, when the bob sinks, the buoyant force is insufficient to support its weight, and it exerts a downward force on the liquid, which also contributes to the total weight. In both scenarios, the weight of the bob is effectively added to the system's total weight. Understanding these forces is crucial for analyzing hydrostatic principles.
harjyot
Messages
42
Reaction score
0
I have a beaker with a liquid of density
rho, and weight = W
now I throw into it s Bob say, of density rho' and weight=w.
can anyone explain what will be total new weight,with all forces explained for the cases:
body floats.
body sinks
 
Physics news on Phys.org
What do you think the new weight will be? Why not try to describe all the forces acting on that bob in both cases?
 
the force on the Bob will be
weight - upthrust.
by total weight I mean the weight of the whole system
 
harjyot said:
the force on the Bob will be
weight - upthrust.
OK.

When the bob is floating, the forces on the bob are weight (down) and the buoyant force (up). They must balance if it floats.

When the bob sinks, the buoyant force is not enough to support the weight of the bob. When the bob settles on the bottom of the beaker, the bottom of the beaker will exert an upward force on it.
by total weight I mean the weight of the whole system
Right. So what do you think happens to the total weight of the system?
 
in the first case, when it floats, the Bob pushes the liquid down with It's weight. so the total weight is W+weight of Bob

when it sinks, the net force on Bob is upthrust + reaction force = weight.
here too the weight of Bob gets added?
 

Thread '1:1 versus 2:1 Mechanical Advantage debate'

The rope is tied into the person (the load of 200 pounds) and the rope goes up from the person to a fixed pulley and back down to his hands. He hauls the rope to suspend himself in the air. What is the mechanical advantage of the system? The person will indeed only have to lift half of his body weight (roughly 100 pounds) because he now lessened the load by that same amount. This APPEARS to be a 2:1 because he can hold himself with half the force, but my question is: is that mechanical...
View full post »

Thread 'Average velocity as a weighted mean'

Hello everyone, Consider the problem in which a car is told to travel at 30 km/h for L kilometers and then at 60 km/h for another L kilometers. Next, you are asked to determine the average speed. My question is: although we know that the average speed in this case is the harmonic mean of the two speeds, is it also possible to state that the average speed over this 2L-kilometer stretch can be obtained as a weighted average of the two speeds? Best regards, DaTario
View full post »

Thread 'Newton's first law?'

Some physics textbook writer told me that Newton's first law applies only on bodies that feel no interactions at all. He said that if a body is on rest or moves in constant velocity, there is no external force acting on it. But I have heard another form of the law that says the net force acting on a body must be zero. This means there is interactions involved after all. So which one is correct?
View full post »

Similar threads

I Apparent Weight problem (falling beam)
Replies
2
Views
2K
B Pressure of air inside a glass
Replies
3
Views
2K
I Mass of Backpack in Moving Elevator
Replies
10
Views
2K
"Air Pressure" is not "the weight of the air above you"
Replies
27
Views
4K
I How can you make a free body diagram for someone running then sliding?
Replies
7
Views
2K
Rotation around a non fixed axis + linear motion of a system
Replies
21
Views
4K
Would the upward force be equal to weight of immersed body
Replies
16
Views
3K
Apparent weight of body immersed in liquid
Replies
4
Views
2K
What is the free-body diagram for a massless pulley in free fall?
Replies
31
Views
4K
B Calculate needed dimensions of table - Center of mass, levers etc
Replies
11
Views
2K

Hot Threads

Recent Insights

Back
Top