Physics - Properties of fluids
Fluids- any liquids or gases as they can flow. Unlike solids.
Does forces between atoms matter in fluids? -- Yes, but not in the same
way as solids. Solids have Strong interatomic forces → elasticity and
rigidity. Liquids & gases: Weaker forces → flow, pressure, viscosity,
surface tension.
Hydrostatic Pressure- Pressure in a liquid that increases with depth.
Pressure depends on: Depth, Density of liquid, Gravity so more
deeper -> means more pressure.
Ex: Dam walls are thicker at the bottom because the pressure of
water increases as we go deeper. At greater depth, water exerts
more pressure on the walls, so the lower part of the dam must be
made thicker to withstand this higher pressure.
Pascal’s Law states: The Pressure applied to an enclosed fluid is
transmitted equally in all directions. – byheart this tho: - When
pressure is applied at any part of an enclosed liquid, it is
transmitted equally to every point of the liquid as well as to the
walls of the container.
Applications: Hydraulic lift, Hydraulic jack (used in service
centres - 📌 This is why a small force can lift a heavy car or truck
Surface Tension: it is the attractive force that causes the surface
of a liquid to behave like a stretched elastic membrane due to
Property of cohesive forces between liquid molecules. Examples:
Mosquitoes walking on water, Water droplets forming spheres. 📌
Humans can’t walk on water because our weight is much larger →
surface tension breaks
Viscosity: Viscosity is the property of a fluid by which it resists the
flow between its layers.. (Water flows easily → low viscosity ,
Honey flows slowly → high viscosity , Walking in water is harder
than walking on land) - 📌 Higher viscosity → slower flow
Bernoulli’s Principle- Bernoulli’s principle states that for a fluid in
steady flow, the sum of pressure energy, kinetic energy and
potential energy per unit volume remains constant. Explains: Why
water sprays farther when a pipe opening is pressed, How a
cricket ball swings , How airplanes take off . -- 📌 Faster air on
top of wings → lower pressure → lift
Topic- HYDROSTATIC PRESSURE definition : The pressure exerted
by a fluid at rest is called hydrostatic pressure.
Pressure depends on force and area, i.e same force on smaller area -> greater effect,
larger area -> smaller effect. Pressure is defined as the effect of force acting per unit
area. Mathematically: Pressure = Force / Area.
, The side walls of a dam are thicker at the base. The walls of rooms in a house are of
uniform thickness. Reason:Pressure in liquids increases with depth, The bottom of a dam
experiences greater pressure, so it must be thicker to withstand it.
Behaviour of Solids and Fluids: Solids: Develop shearing stress when changed in
shape by an external force. ( shearing stress- sliding stress, the solids slide against
eachother to change shape). This is because inter-atomic forces in solids are very large
fluids (liquids and gases): Do not develop shearing stress and Cannot resist change in
shape due to shear forces.
Force Exerted by Fluids - When an object is submerged in a fluid: The force exerted by the
fluid acts normal (perpendicular) to the surface of the object.
A fluid also exerts force on: The walls of its container and The force acts normal to the
walls at all points
Definition of Pressure in Fluids - The normal force (or thrust) per unit area exerted by a
fluid is called pressure. Pressure is denoted by P. Pressure = thrust/area
SI Unit of Pressure ; The SI unit of pressure is N m ⁻² (newton per square metre). This
unit is also called pascal (Pa). by Blaise Pascal.
Hydrostatic Pressure at a Point Inside a Liquid
Net upward force: P₁ A − P₂ A
mass of the liquid in cylinder = density × volume of the cylinder = ρ. A. h
(where ρ is the density of the liquid, acceleration due to gravity, height of liquid, A
=cross-sectional area of cylinder)
∴ Weight of the liquid in the cylinder = ρ. g. h. A
Since the cylinder is in equilibrium, the resultant force acting or it must be equal to zero.
Pressure at the bottom of a liquid column of height h: P = ρgh ( This shows that:
Hydrostatic pressure due to a fluid increases linearly with depth, hence why thickness
of the wall of a dam is increased with increase in depth)
Absolute Pressure at a Depth -- P= Patm+ρgh ( Pₐₜₘ (pressure on top face- atmospheric
pressure). This P is the absolute pressure at a depth below the
surface.
Effect of Shape of the Vessel- Pressure at a given depth in a liquid is independent of the
shape of the vessel.
Atmospheric Pressure:- The pressure exerted by the atmosphere is
called atmospheric pressure.
German scientist O.V. Guericke demonstrated force due to atmospheric pressure.
Effect of atmospheric pressure: It exerts a large force on bodies,
capable of holding objects together or resisting motion when the
internal pressure is lower.
Torricelli used hydrostatic pressure formula to measure
atmospheric pressure. at equilibrium, atmospheric pressure
equals the pressure of any fluid column exposed to it.
, Buoyancy is the upward force a fluid (liquid or gas) exerts on a submerged or floating object,
opposing gravity. Lifting an object in water is easier than in air. Reason:
Difference in upward forces exerted by the fluid. The upward force on an object
submerged in a fluid is called buoyant force.
Archimedes’ Principle: Discovered by Archimedes- It states: When an
object is submerged partially or fully in a fluid, the magnitude of
the buoyant force on it is always equal to the weight of the fluid
displaced by the object. Ex: Hot air balloon: Hot air has less density (weight)
than cold air, Net upward buoyant force lifts the balloon → floats
Floating objects: When the below two forces balance each other,
the object is said to be floating on water.
When an object is in equilibrium in a fluid, there are two main
forces acting on it: 1. Gravitational force (weight) acting
downwards 2. Buoyant force exerted by the displaced fluid acting
upwards. This means that a floating body displaces a volume of
fluid equal to its own weight.
Pascal’s Law: Daily applications of this law: 1. A bus driver
stopping the bus by applying a small force on the brakes 2.
Hydraulic jacks or lifts used to lift cars or trucks 3. Packing of
cotton bales using hydraulic presses
Definition / Principle (Pascal’s Law): When pressure is applied at
any part of an enclosed liquid, it is transmitted undiminished to
every point of the liquid as well as to the walls of the container.
This law is also known as the law of transmission of liquid
pressure.
Applications of Pascal’s Law : A. Hydraulic Press / Balance / Jack / Lift: A
hydraulic press is a simple device based on Pascal’s law. It is
used to lift heavy loads by applying a small force.
Basic arrangement: Smaller piston: area = A₁, force applied =
F₁ . Larger piston: area = A₂, platform carries heavy load. The
pressure on the smaller piston(thing used to lift car) is
transmitted undiminished to the larger piston through the liquid.
Fluids- any liquids or gases as they can flow. Unlike solids.
Does forces between atoms matter in fluids? -- Yes, but not in the same
way as solids. Solids have Strong interatomic forces → elasticity and
rigidity. Liquids & gases: Weaker forces → flow, pressure, viscosity,
surface tension.
Hydrostatic Pressure- Pressure in a liquid that increases with depth.
Pressure depends on: Depth, Density of liquid, Gravity so more
deeper -> means more pressure.
Ex: Dam walls are thicker at the bottom because the pressure of
water increases as we go deeper. At greater depth, water exerts
more pressure on the walls, so the lower part of the dam must be
made thicker to withstand this higher pressure.
Pascal’s Law states: The Pressure applied to an enclosed fluid is
transmitted equally in all directions. – byheart this tho: - When
pressure is applied at any part of an enclosed liquid, it is
transmitted equally to every point of the liquid as well as to the
walls of the container.
Applications: Hydraulic lift, Hydraulic jack (used in service
centres - 📌 This is why a small force can lift a heavy car or truck
Surface Tension: it is the attractive force that causes the surface
of a liquid to behave like a stretched elastic membrane due to
Property of cohesive forces between liquid molecules. Examples:
Mosquitoes walking on water, Water droplets forming spheres. 📌
Humans can’t walk on water because our weight is much larger →
surface tension breaks
Viscosity: Viscosity is the property of a fluid by which it resists the
flow between its layers.. (Water flows easily → low viscosity ,
Honey flows slowly → high viscosity , Walking in water is harder
than walking on land) - 📌 Higher viscosity → slower flow
Bernoulli’s Principle- Bernoulli’s principle states that for a fluid in
steady flow, the sum of pressure energy, kinetic energy and
potential energy per unit volume remains constant. Explains: Why
water sprays farther when a pipe opening is pressed, How a
cricket ball swings , How airplanes take off . -- 📌 Faster air on
top of wings → lower pressure → lift
Topic- HYDROSTATIC PRESSURE definition : The pressure exerted
by a fluid at rest is called hydrostatic pressure.
Pressure depends on force and area, i.e same force on smaller area -> greater effect,
larger area -> smaller effect. Pressure is defined as the effect of force acting per unit
area. Mathematically: Pressure = Force / Area.
, The side walls of a dam are thicker at the base. The walls of rooms in a house are of
uniform thickness. Reason:Pressure in liquids increases with depth, The bottom of a dam
experiences greater pressure, so it must be thicker to withstand it.
Behaviour of Solids and Fluids: Solids: Develop shearing stress when changed in
shape by an external force. ( shearing stress- sliding stress, the solids slide against
eachother to change shape). This is because inter-atomic forces in solids are very large
fluids (liquids and gases): Do not develop shearing stress and Cannot resist change in
shape due to shear forces.
Force Exerted by Fluids - When an object is submerged in a fluid: The force exerted by the
fluid acts normal (perpendicular) to the surface of the object.
A fluid also exerts force on: The walls of its container and The force acts normal to the
walls at all points
Definition of Pressure in Fluids - The normal force (or thrust) per unit area exerted by a
fluid is called pressure. Pressure is denoted by P. Pressure = thrust/area
SI Unit of Pressure ; The SI unit of pressure is N m ⁻² (newton per square metre). This
unit is also called pascal (Pa). by Blaise Pascal.
Hydrostatic Pressure at a Point Inside a Liquid
Net upward force: P₁ A − P₂ A
mass of the liquid in cylinder = density × volume of the cylinder = ρ. A. h
(where ρ is the density of the liquid, acceleration due to gravity, height of liquid, A
=cross-sectional area of cylinder)
∴ Weight of the liquid in the cylinder = ρ. g. h. A
Since the cylinder is in equilibrium, the resultant force acting or it must be equal to zero.
Pressure at the bottom of a liquid column of height h: P = ρgh ( This shows that:
Hydrostatic pressure due to a fluid increases linearly with depth, hence why thickness
of the wall of a dam is increased with increase in depth)
Absolute Pressure at a Depth -- P= Patm+ρgh ( Pₐₜₘ (pressure on top face- atmospheric
pressure). This P is the absolute pressure at a depth below the
surface.
Effect of Shape of the Vessel- Pressure at a given depth in a liquid is independent of the
shape of the vessel.
Atmospheric Pressure:- The pressure exerted by the atmosphere is
called atmospheric pressure.
German scientist O.V. Guericke demonstrated force due to atmospheric pressure.
Effect of atmospheric pressure: It exerts a large force on bodies,
capable of holding objects together or resisting motion when the
internal pressure is lower.
Torricelli used hydrostatic pressure formula to measure
atmospheric pressure. at equilibrium, atmospheric pressure
equals the pressure of any fluid column exposed to it.
, Buoyancy is the upward force a fluid (liquid or gas) exerts on a submerged or floating object,
opposing gravity. Lifting an object in water is easier than in air. Reason:
Difference in upward forces exerted by the fluid. The upward force on an object
submerged in a fluid is called buoyant force.
Archimedes’ Principle: Discovered by Archimedes- It states: When an
object is submerged partially or fully in a fluid, the magnitude of
the buoyant force on it is always equal to the weight of the fluid
displaced by the object. Ex: Hot air balloon: Hot air has less density (weight)
than cold air, Net upward buoyant force lifts the balloon → floats
Floating objects: When the below two forces balance each other,
the object is said to be floating on water.
When an object is in equilibrium in a fluid, there are two main
forces acting on it: 1. Gravitational force (weight) acting
downwards 2. Buoyant force exerted by the displaced fluid acting
upwards. This means that a floating body displaces a volume of
fluid equal to its own weight.
Pascal’s Law: Daily applications of this law: 1. A bus driver
stopping the bus by applying a small force on the brakes 2.
Hydraulic jacks or lifts used to lift cars or trucks 3. Packing of
cotton bales using hydraulic presses
Definition / Principle (Pascal’s Law): When pressure is applied at
any part of an enclosed liquid, it is transmitted undiminished to
every point of the liquid as well as to the walls of the container.
This law is also known as the law of transmission of liquid
pressure.
Applications of Pascal’s Law : A. Hydraulic Press / Balance / Jack / Lift: A
hydraulic press is a simple device based on Pascal’s law. It is
used to lift heavy loads by applying a small force.
Basic arrangement: Smaller piston: area = A₁, force applied =
F₁ . Larger piston: area = A₂, platform carries heavy load. The
pressure on the smaller piston(thing used to lift car) is
transmitted undiminished to the larger piston through the liquid.
