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Questions and Answers
What is the definition of pressure in a fluid?
What is the definition of pressure in a fluid?
What volume characteristic does pressure in a liquid depend on?
What volume characteristic does pressure in a liquid depend on?
Which of the following correctly describes the relationship between temperature and gas pressure?
Which of the following correctly describes the relationship between temperature and gas pressure?
How does the compressibility of liquids compare to that of gases?
How does the compressibility of liquids compare to that of gases?
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What does density measure about a substance?
What does density measure about a substance?
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Which of the following factors does NOT affect the pressure of a fluid in an open container?
Which of the following factors does NOT affect the pressure of a fluid in an open container?
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In the formula for pressure, what does the symbol 'P' represent?
In the formula for pressure, what does the symbol 'P' represent?
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What causes gas pressure within a container?
What causes gas pressure within a container?
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What is the state of an object when the resultant of all forces acting on it is zero?
What is the state of an object when the resultant of all forces acting on it is zero?
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When resolving a tension force, which components are derived from it?
When resolving a tension force, which components are derived from it?
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What occurs when a car is pushed at one end with a force that is exactly opposed by a similar force at the other end?
What occurs when a car is pushed at one end with a force that is exactly opposed by a similar force at the other end?
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What is the formula for calculating a load moment?
What is the formula for calculating a load moment?
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Which statement is true regarding the balance of a lever system?
Which statement is true regarding the balance of a lever system?
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What is a primary function of a simple machine, like a lever?
What is a primary function of a simple machine, like a lever?
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In the context of equilibrium, what does it mean for scales to be balanced but not in equilibrium?
In the context of equilibrium, what does it mean for scales to be balanced but not in equilibrium?
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How does a smaller effort force contribute to moving a heavier load using a lever?
How does a smaller effort force contribute to moving a heavier load using a lever?
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What is the main purpose of a lever?
What is the main purpose of a lever?
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In a first-class lever, where is the fulcrum located in relation to the load and effort?
In a first-class lever, where is the fulcrum located in relation to the load and effort?
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What is the formula for calculating mechanical advantage (MA) in a lever?
What is the formula for calculating mechanical advantage (MA) in a lever?
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If the load (L) is 100 kg and the effort (E) is 10 kg, what is the mechanical advantage (MA)?
If the load (L) is 100 kg and the effort (E) is 10 kg, what is the mechanical advantage (MA)?
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Which of the following is an example of a second-class lever?
Which of the following is an example of a second-class lever?
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What is meant by 'leverage' in the context of a first-class lever?
What is meant by 'leverage' in the context of a first-class lever?
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In a first-class lever, if the lifting arm is twice the length of the load arm, how much less effort is needed to lift the load?
In a first-class lever, if the lifting arm is twice the length of the load arm, how much less effort is needed to lift the load?
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What characteristic of a first-class lever allows a load to be moved with less effort?
What characteristic of a first-class lever allows a load to be moved with less effort?
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What type of stress develops in the direction opposite to a twist?
What type of stress develops in the direction opposite to a twist?
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Which aspect can cause internal stress during heat treatment of metals?
Which aspect can cause internal stress during heat treatment of metals?
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What is commonly referred to as 'Locked In Stress'?
What is commonly referred to as 'Locked In Stress'?
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What initiates a crack that may lead to fatigue failure?
What initiates a crack that may lead to fatigue failure?
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Which of the following can be considered a 'stress raiser' contributing to fatigue failure?
Which of the following can be considered a 'stress raiser' contributing to fatigue failure?
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In which types of vehicles are fatigue failures reported to be quite common?
In which types of vehicles are fatigue failures reported to be quite common?
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What is the effect of temperature changes during operation on moving parts?
What is the effect of temperature changes during operation on moving parts?
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What formation within materials is likely to act as stress raisers over time?
What formation within materials is likely to act as stress raisers over time?
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What directly influences atmospheric pressure at a given location?
What directly influences atmospheric pressure at a given location?
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How is Absolute Pressure calculated in relation to Gauge Pressure?
How is Absolute Pressure calculated in relation to Gauge Pressure?
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At an altitude of 29,000 ft, if the outside pressure is 4.4 psi, what is the differential pressure experienced by the aircraft cabin set at 11 psi?
At an altitude of 29,000 ft, if the outside pressure is 4.4 psi, what is the differential pressure experienced by the aircraft cabin set at 11 psi?
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Which of the following best describes a solid?
Which of the following best describes a solid?
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Which statements accurately describe fluids?
Which statements accurately describe fluids?
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What is a characteristic of Gauge Pressure as compared to Absolute Pressure?
What is a characteristic of Gauge Pressure as compared to Absolute Pressure?
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Which of these must occur for an aircraft to maintain structural integrity at cruising altitude?
Which of these must occur for an aircraft to maintain structural integrity at cruising altitude?
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What is true regarding the properties of metals as solids?
What is true regarding the properties of metals as solids?
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Study Notes
Buoyancy and Pressure in Liquids
- Liquids and gases are both fluids, therefore the theory behind buoyancy and pressure in liquids and gases is similar.
- Liquids have a constant density, while gases are compressible.
Pressure in Solids
- Pressure is defined as Force per unit area.
- Pressure = Force / Area.
- Using g = 10 m/s per s.
Pressure in Gases
- The molecules in a substance move around more rapidly when heated, as its thermal energy increases.
- There is a direct relationship between the temperature of a substance and the motion energy of its molecules.
- Gas pressure is the result of the continual bombardment of the walls of the container.
Pressure in Fluids
- Pressure is still defined as force per unit area, but in a fluid it is caused by the continual bombardment of the molecules against the inside of the container.
- The pressure exerted by a column of fluid in an open container is determined by:
- the vertical height of the column
- gravity
- density of the fluid
- The pressure is not affected by the volume of the liquid.
Density and Specific Gravity
- Density is defined as the mass per unit volume of a substance.
- A given volume of lead has many times the mass of the same volume of water.
- When the density of other solids or liquids are compared to water, a table of comparative densities or specific gravities can be determined.
Resolution of a Vector
- A tension force can be resolved into two components:
- horizontal
- vertical
- This can be done using standard trigonometric ratios.
Resultant Force and Equilibrium
- Sometimes, forces act at different directions on a body.
- In such cases, forces must be resolved to calculate a resultant net force.
- When an object does not change its state of motion or rest, the resultant of all the forces acting on it is zero, and it is said to be in a state of equilibrium.
Moments
- Load Moment = (load x load arm)
- Effort Moment = (force x effort arm)
- Either side of the lever has a moment which is the force multiplied by the distance, called the arm from the fulcrum.
- The system is balanced when the load moment and the effort moment are equal.
- The smaller effort force moves through a larger arc to raise the heavier load a small distance.
Levers
- A lever is a simple machine.
- A simple machine is a device which provides a mechanical advantage.
- The purpose of a lever is to perform work:
- for a load (L) to be lifted
- by an effort (E)
- pivoting around a fulcrum (F)
- If the load moved is greater than the effort used, the machine has a positive mechanical advantage.
First Class Lever
- An example of a first-class lever is a crowbar.
- The fulcrum is situated between the load and the effort.
- The load is greater than the effort.
- MA = Load / Effort
- The lid only needs to be raised a short distance but your hand travels a larger distance.
First Class Lever (cont'd)
- If L is 100 kg and E is 10, MA = 10.
- The ratio of the distance moved by each end of the lever will also equal 10. Distance Ratio = MA.
Mechanical Advantage
- The mechanical advantage of a first-class lever depends on the distance moved by effort compared to load.
- The load can be lifted with 7 times less effort if the lifting arm is 7 times the length of the load arm.
Residual Stress
- Abrupt or uneven temperature changes tend to cause internal stress.
- This often occurs when heat-treating metals.
- This effect often explains why a component fails in service even though its externally applied stress levels are low.
- Can be beneficial, such as in car windshields.
- Also called “Locked In Stress”.
Fatigue
- During operation, moving parts experience a variety of loadings, such as vibration, changes of load, and temperature changes.
- Repeated applications of small loads may eventually result in fatigue failure.
- A crack can originate at the point of highest tensile stress in the part.
- Fatigue failures are quite common in aircraft and motor cars.
- Fatigue failures are at least as common as overload failures.
Fatigue (cont'd)
- Surface damage like nicks, cuts, scratches, gouges, cracks, or corrosion pits can cause a fatigue failure at that point.
- These so called ‘stress raisers’ also occur where a part has an abrupt change in shape or section thickness.
- For this reason sharp edges should be avoided.
- Flaws beneath the surface of materials are also stress raisers.
- Fatigue failures happen chiefly with metals.
Atmospheric Pressure
- Atmospheric pressure at a location depends on the weight of the column of air above that location.
Absolute Pressure vs. Gauge Pressure
- Gauge pressure reads pressure above (or below) atmospheric.
- Absolute Pressure is Gauge Pressure plus Atmospheric Pressure.
Differential Pressure
- Modern aircraft retain a cabin altitude equivalent to 8000’ or 11 psi.
- Cruising at 29,000 ft, the outside pressure is 4.4 psi.
- Therefore, the structure of the aircraft is experiencing a differential pressure of 11 - 4.4 = 6.6.psi
- This is a significant component of the total stress on the airframe.
Solids
- Solids have a definite shape and definite volume which is independent of its container.
- The forces (bonds) that keep the atoms or molecules together are strong.
- Therefore, a solid does not require outside support to maintain its shape.
- Most metals are solids and as such are usually hard and strong and capable of being shaped mechanically (malleable and ductile).
Fluids
- Both liquids and gases are classified as fluids.
- The force exerted by a fluid at any point on the surface of a submerged object is perpendicular to the surface of the object.
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Description
Test your understanding of buoyancy and pressure in liquids, gases, and solids. This quiz covers the fundamental principles that govern how pressure operates in different states of matter and the relationships between temperature, force, and area. Challenge yourself to apply these concepts accurately.