This document is a chapter from a Physics textbook that discusses buoyant force. It defines key terms like upthrust, buoyancy, density, and immerse. It explains Archimedes' principle that the buoyant force equals the weight of the fluid displaced. It provides examples of how buoyant force affects whether objects float or sink in liquids and gases. It also shows how to calculate buoyant force using the formula that it equals fluid density times gravity times the volume of fluid displaced. There are also example problems solving for buoyant force and weight based on given dimensions and densities.

1. “БІЛІМ-Инновация”
Халықаралық қоғамдық қоры
PHYSICS CHAPTER 5.8
4-term Week 2-3 2019-2020
Buoyant force
Textbook page
82

2. CHAPTER 5.8 Buoyant force
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You will be able to:
• 7.3.1.12 – to explain the nature of buoyant forces in liquids and
gases;
• 7.3.1.13 – to apply Archimedes' principle in solving problems

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TERMS:
• UPTHRUST
• BUOYANCY
• DENSITY
• FLOAT
• SINK
• MERCURY
• IMMERSE
- жоғары итеру / выталкивающая сила
- жүзгіштік / плавучесть
- тығыздық / плотность
- сұйықтықтың бетінде қалу / плавать на
поверхности жидкости
- бату/ тонуть
- сынап / ртуть
- батыру / погрузить
CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force
Archimedes' Principle

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force
From Archimedes’s Principle :
Buoyant Force = Weight of fluid displaced
= mg
= ρVg (note : ρ = m )
V
Thus FB = ρ g V
Where ……
FB = Buoyant Force or Upthrust (N, Newtons)
ρ = Density of fluid (kg/m3)
V = Volume of fluid displaced or (m3)
the volume of the object that immersed in the fluid.

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CHAPTER 5.8 Buoyant force
At what depth is the buoyant
force acting on the brick at its
greatest?

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force
Floating objects

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CHAPTER 5.8 Buoyant force
lighter object heavier object too heavy
The weight of displaced
water is less than the
weight of the object

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force
Hot air balloon
1. rises upwards
(Upthrust > Weight of hot air (helium gas) + weight of airship fabric
+ weight of gondola + weight of passengers.)( balloon expand)
2..descends
(Upthrust < Weight of hot air (helium gas) + weight of airship
fabric + weight of gondola + weight of passengers.)(balloon shrinks)
3. stationary
(Upthrust = Weight of hot air (helium gas) + weight of airship fabric
+ weight of gondola + weight of passengers.)( balloon size uncanged)
Buoyant force and Floatation in gases

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CHAPTER 5.8 Buoyant force
Buoyant force = weight ⇒ the object floats and stationary
Buoyant force > weight ⇒ the object moves up
Buoyant force < weight ⇒ the object moves down
Buoyant force and Floatation in liquids

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force
Given:
Dimensions of change of the displaced water: a=2 m, b=3 m, c=0,12 m
Density of water = 1000 kg/m
The barge with horse floats
Find the weight of horse?
3

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CHAPTER 5.8 Buoyant force
Solution :
Weight of horse = Buoyant force
Given:
Dimensions of change of the displaced water: a=2 m, b=3 m, c=0,12 m
Density of water = 1000 kg/m
The barge with horse floats
Find the weight of horse?
3

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CHAPTER 5.8 Buoyant force
Solution :
Weight of horse = Buoyant force
Weight of horse = ρ g V = ρ g (abc)=1000*10*(2*3*0,12)=7200 N
Given:
Dimensions of change of the displaced water: a=2 m, b=3 m, c=0,12 m
Density of water = 1000 kg/m
The barge with horse floats
Find the weight of horse?
3

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CHAPTER 5.8 Buoyant force
Solution :
Weight of horse = Buoyant force
Weight of horse = ρ g V = ρ g (abc)=1000*10*(2*3*0,12)=7200 N
Result: Weight of horse = 7200 N or 720 kg
Given:
Dimensions of change of the displaced water: a=2 m, b=3 m, c=0,12 m
Density of water = 1000 kg/m
The barge with horse floats
Find the weight of horse?
3

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force

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CHAPTER 5.8 Buoyant force
Plimsoll line of the ship

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CHAPTER 5.8 Buoyant force
Plimsoll line of the ship

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- Physics 7 grade, Астана кітап
- https://science.howstuffworks.com/transport/engines-
equipment/submarine1.htm
- https://en.wikipedia.org/wiki/Buoyancy
- https://www.bbc.co.uk/bitesize/guides/z9ykmsg/revision/4
Resources
CHAPTER 5.8 Buoyant force