LECTURE 2 - 1ST SEM Flashcards
1ST SEMESTER PHYSICS
What are fluids?
Things which flow (including liquids and gas)
What is a solid-state?
Characterized by internal order and fixed atomic position. Helping it keep the shape.
What is a liquid state?
When atoms or molecules have strong very cohesive forces that hold them together
How do molecules behave in liquids?
- Free to move relative to one another
- Readily take shape of container
- Flow readily, using considerable force to seperate molecules
Why are liquids considered incompressible?
As cannot occupy smaller volume without the exertion of enormous pressures
What is the formula for pressure?
P = F/A
How is pressure created in gas?
No attractive forces between molecules and only forces is exerted via collisions.
How can the penetrating ability of an object be determined?
Depends largely upon the pressure rather than just the force
Why do hypodermic needles have large penetrating pressure?
- They have an extremely small tip area where small force can result in large penetrating pressure
- Sharper needles require less force to produce high penetrating pressure.
What is the formula for pressure in liquids? What does the formula indicate?
P=p (fluid density) x g (acceleration due to gravity) x h (fluid depth)
Pressure caused by liquid is proportional to the depth of liquid and density.
Absolute pressure is the sum of atmospheric pressure and liquid pressure.
What factors determine the pressure in a container in a liquid?
Depth of liquid and not shape
What is the theory behind pressure distributed in static liquid?
- Pressure is exerted equally in all directions in static liquid
- At any given depth, it is found that equilibrium that forces are exerted upon it in all directions
- Forces must be exerted in pairs such that the net force is zero
How does pressure behave in a given vessel?
- Pressure increases with depth.
- Horizontal pressure on the walls also increase.
How does pressure work in I.V Apparatus?
- Pressure is determined by height of the liquid surface above the point of input in patient
- Pressure is transmitted through the tubing, even if coils are present
- Pressure at the patient under static (no flow) conditions would be the same regardless of the configuration of the tubing
(refer to the diagram)
What is pascals principle in the transmission of pressure?
Any changes of pressure in an enclosed fluid are transmitted undiminished to all parts of the fluid
How can Pascal’s principle be applied clinically?
- Prevention of pressure sores
- Through cerebrospinal fluid in the spinal cord
- Protection of unborn fetus through the protection of external forces
- Through enclosed fluid in the eye
- To explain the effects of collected fluid in the pericardial and pleural cavities
How can pascals principle help in the prevention of pressure sores?
- Through the use of air or water matters helps prevent the formation of decubitus ulcers
- Through using air/water mattresses allows for a closed fluid system, allowing pressure to be evenly distributed.
- When the patient lies on the mattress, the same pressure is exerted against every part of the body which is in contact with the mattress.
How does pressure (pascals laws) cause pressure sores?
Decubitus ulcers (bed sores) can be caused by ordinary pressure sores due to large pressure being exerted on parts at risk
What is buoyancy?
- Is the lifting force requ
What is Archimedes’ principle?
- Is when a buoyant force arises from a difference in liquid pressure above and below the object.
- The buoyant force on the submerged object becomes equal to the weight of the liquid that is displaced.
What is buoyancy?
How does buoyancy affect the weight of an object?
the ability or tendency of something to float in water or other fluid.
- Buoyancy causes an object to weigh less than it does in the air
What does a hydrometer measure?
- Measures the specific gravity of a liquid, by floating a glass tube in a liquid.
- If gravity of liquid is increased, it causes the hydrometer to float higher.
What can a hydrometer be used to measure clinically?
It can be a urinometer - to measure the gravity of urine, an important physiological indicator as some diseases alter the composition of urine that change the gravity
Why do objects weigh less in water than in air?
- When weighed in water, buoyant forces equal to the weight of water that is displaced.
- Causing the difference in weight between air and water
What is laminar flow?
- This is when the average flow speed is about half the maximum speed found at the center.
- It represents the minimum energy loss
What causes turbulent flow?
- Is when the flow is speeded up past a certain critical speed or there is an obstruction in the flow path
- Causing eddies to form and laminar flow to break down
How does pressure behave in non- or flowing fluids?
Pressure hit at all points in horizontal tubes when there is no flow
Uniform pressure drops when there is smooth flow
What is the formula for volume flow rate?
Volume flow rate = Volume/Time
What is the formula to represent the relationship of the smooth flow of an ideal fluid?
F = P1 - P2
——————-
R
R = Effective resistance to flow
F = Volume flow rate
P1 & P2 = Pressures at the upstream and downstream ends of the tube
How does fluid flow through a tube?
- Fluid flows in a smooth layer.
- The layer nearest the wall will be at rest.
- Speed gradually increases to a maximum on the central axis of the vessel
Why is important to maintain laminar flow clinically?
- It allows for efficient fluid circulation - in things like intravenous fluid apparatus or circulatory system of the body
How can turbulent flow be prevented clinically?
- By making smooth transitions to different tube sizing.
What is the formula for Poiseuile law?
Q = πr^4P
——————
8ηL
Q = flow rate
η = Fluid viscosity
L = Pipe Length
P = Pressure difference between the ends
What is Poiseuille’s Law?
The laminar flow rate of an incompressible fluid along a pipe is proportional to the fourth power of the pipe’s raduis.
What is the relationship between blood viscosity and fluid pressure?
- Viscosity of blood is found to decrease with increasing fluid pressure
- Implies that the flow rate would be more than doubled by doubling the pressure gradient.
