Physical Science Chapter on Gases and Liquids

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Questions and Answers

What is a key characteristic that distinguishes gases from liquids?

Gases are incompressible.

Gases can expand continuously. (correct)

Gases have a fixed volume.

Gases exert a force only at the surface.

Which property describes the ability of a gas to change volume easily?

Elasticity

Compressibility (correct)

Tension

Incompressibility

What happens to a gas when pressure is applied while keeping the temperature constant?

The gas condenses into a liquid.

The pressure stays the same.

The volume decreases. (correct)

The gas expands indefinitely.

Which force described is exerted by a fluid on the walls of its container?

Normal force Signup and view all the answers

Which concept involves the study of how materials deform under applied forces?

Theory of stress and strain Signup and view all the answers

What is the primary reason liquids are considered incompressible?

They maintain a constant density. Signup and view all the answers

How is pressure defined?

Pressure = Force per unit area Signup and view all the answers

What factors determine the pressure exerted by a column of fluid in an open container?

Height, gravity, and density of the fluid Signup and view all the answers

What principle explains the relationship between the temperature of a gas and the motion of its molecules?

Direct relationship principle Signup and view all the answers

Which of the following correctly describes how pressure changes with the volume of a liquid?

Volume does not affect pressure in a liquid. Signup and view all the answers

Which statement regarding gas pressure is accurate?

Gas pressure results from molecules striking the walls of their container. Signup and view all the answers

What is defined as mass per unit volume?

Density Signup and view all the answers

What happens to gas molecules when a gas is heated?

They move more rapidly. Signup and view all the answers

What happens to the resultant force when an object is in a state of equilibrium?

It is equal to zero. Signup and view all the answers

How is a force resolved into its components?

Using standard trigonometric ratios. Signup and view all the answers

In a lever system, what is the relationship for balance between load moment and effort moment?

Load moment equals effort moment. Signup and view all the answers

What defines a simple machine like a lever?

It provides a mechanical advantage. Signup and view all the answers

What occurs when two equal forces act in opposite directions on an object?

The object stays at rest or remains in a state of motion. Signup and view all the answers

What is the term for the distance from the fulcrum to where the force is applied in a lever system?

Effort arm. Signup and view all the answers

When calculating the moment in a lever system, what does 'load moment' specifically refer to?

Load times load arm. Signup and view all the answers

Why are scales balanced but not in equilibrium when opposing forces are equal?

Because forces are not acting at the same line. Signup and view all the answers

What must be done to rectify an unbalanced condition in rotating components?

Shift the center of gravity to align with the center of rotation. Signup and view all the answers

Which rotating components are typically balanced during manufacture?

Landing-gear wheel assemblies, helicopter rotors, and fans. Signup and view all the answers

What happens to a perfectly balanced propeller when subjected to air movements?

It remains stationary in any position. Signup and view all the answers

What is the correct formula for stress?

Stress = F / A Signup and view all the answers

According to Hooke's Law, what is the relationship between strain and stress?

Strain is directly proportional to stress within the elastic limit. Signup and view all the answers

Which statement about strain is true?

Strain measures deformation as a percentage of original size. Signup and view all the answers

What does the term 'velocity ratio' represent in a system?

The direct ratio of two speeds present in the system Signup and view all the answers

What can happen if a component spins at very high speeds with even a tiny amount of unbalance?

It may produce excessive vibration. Signup and view all the answers

In a pulley system with a mechanical advantage (MA) of 4, what is the relationship between the speeds of the operator and the load?

The rope is pulled four times faster than the load is raised Signup and view all the answers

What defines a couple in mechanics?

Two equal forces acting in parallel but opposite directions Signup and view all the answers

What occurs when the strain exceeds the material's elastic limit?

The material will permanently deform. Signup and view all the answers

What is the formula for calculating the torque produced by a couple?

T = F x b Signup and view all the answers

How is the Centre of Gravity (CG) of a body determined for regularly shaped bodies of uniform density?

The CG is at the geometric center of the body Signup and view all the answers

How can the Centre of Gravity of an irregularly shaped solid be determined?

By hanging it from two different points and finding the intersection of verticals Signup and view all the answers

What does the entire weight of a body act through?

The vertical passing through its Centre of Gravity Signup and view all the answers

Which of the following statements about a couple is incorrect?

It involves two forces of different magnitudes Signup and view all the answers

When raising a body, where should the upward-acting force be applied to avoid toppling?

Directly below the center of gravity (CG) Signup and view all the answers

Which of the following factors can cause the center of gravity (CG) of an aircraft to shift?

Unequal fuel consumption from tanks Signup and view all the answers

What is the significance of maintaining the CG within acceptable limits in aircraft?

To prevent the aircraft from becoming tail heavy or nose heavy Signup and view all the answers

What is true about a perfectly circular disc with an axle through its center?

It retains balance regardless of added weights if they are balanced diametrically Signup and view all the answers

Which statement best describes the center of gravity (CG) in objects of regular shape?

Variations in thickness can lead to CG displacement Signup and view all the answers

What happens to the CG of an aircraft if equal amounts of fuel are used from both wings?

It has no effect on the CG Signup and view all the answers

Why is it important to lift loads near the center of gravity (CG) of a body?

To avoid toppling during lifting Signup and view all the answers

In what circumstance may the CG not align with the geometric center of a rotating object?

Due to variations in thickness or damaged areas Signup and view all the answers

Study Notes

Module: B-2 Physics, Topic 2.2.1 Statics

Statics is a branch of physics dealing with forces and moments on objects not undergoing any acceleration
Completing this topic allows students to understand interactions of forces, moments, couples, simple machines, and mechanical advantage.
The center-of-gravity of a mass is a key concept within this topic.
Understanding stress, strain, and elasticity principles, including tension, compression, shear, and torsion
Knowledge of the properties of solids, fluids, and gases
Understanding pressure and buoyancy in liquids (e.g., using barometers)
Forces produce changes in a body's motion; starting, stopping, accelerating, or decelerating
Forces can do work when energy is available.
Vectors require magnitude and direction to be fully defined; scalars just require magnitude
Vector addition involves moving one vector to the other's tail, then completing the triangle to find the resultant
A force can be resolved into components using trig ratios
An object is in equilibrium when the resultant force on it is zero, meaning its state of motion or rest does not change
Moments involve force multiplied by their distance from a fulcrum.
Mechanical Advantage (MA) is the ratio of load to effort in a simple machine, useful if the load is greater than the effort
A first-class lever has the fulcrum between load and effort, like a crowbar
The MA is the ratio of load to effort in a first-class lever. A larger MA indicates that less force is needed to lift the load. The distance moved by the effort is larger than the distance moved by the load.
A second-class lever has the load between fulcrum and effort, like a wheelbarrow. A larger MA indicates less force is needed to lift the load. The distance moved by the effort is shorter than the distance moved by the load.
A third-class lever has the effort between fulcrum and load, like ice tongs
A larger MA indicates less force is needed to lift the load, but the distance moved by the effort is shorter than the distance moved by the load.
Velocity ratio is the direct ratio of two speeds in the same system.
A couple is a moment produced by two equal forces acting in parallel and opposite directions
The Centre of Gravity (CG) is the point where the weight of a body appears to act, regardless of its position
Calculating the CG of regular objects with uniform density is straightforward, it is the geometric center
Calculating the CG of irregularly shaped objects involves hanging from different points. The CG is the intersection of the vertical lines
The weight of an object acts vertically through its CG.
An object is stable when the CG is below the supporting base.
The CG of an aircraft will change with weight/passenger/cargo distribution and fuel usage.
Balance of rotating objects considers the effect of center of gravity in situations with axial rotation.
Unbalanced objects exhibit vibrations; balancing techniques involve adding or removing material to the appropriate axis.
Examples of rotating components to consider include propellers, landings, gear wheels, helicopter rotors, compressors, turbines, fans, generators, magnetos, gyroscopes
Stress is the external force acting on an object per unit cross-sectional area.
Strain measures the deformation of a material resulting from stress, calculated as the ratio of extension to original size.
A material's elastic limit dictates its return to its original shape after stress is removed.
Hooke’s Law states that strain is directly proportional to stress within a material's elastic limit. Doubling the stress doubles the strain.
Different forms of stress exist: Tension, compression, shear, torsion and residual stress.
Tension stress is force acting in the direction to pull it apart
Compression is the resistance to external forces trying to push an object together; the weight of an aircraft on a runway
Shear stress involves forcing adjacent layers of materials to slide over one another; often seen in lubrication
Torsional stress is twisting or torque applied, leading to compression in one direction and tension in the opposite direction
Residual stress is internal stress caused by uneven temperature changes, particularly during heat treatment.
Fatigue failure occurs due to repeated small loads causing material degradation; it especially affects metal parts
Surface imperfections (nicks, cuts, scratches, etc.) and abrupt changes in shape/cross sections can act as "stress raisers"
Flaws can exist underneath the surface from manufacturing or other processes; their presence makes items more likely to fatigue
Liquids are considered incompressible and maintain a constant density; gases are compressible with volume dependent on the pressure and temp.
Pressure in solids is force divided by area. Using a large area reduces the pressure impact that could exert on a surface
Pressure in fluids depends on the fluid's vertical height, gravity, and density unlike surface area
Pressure in gases— molecules impacting container walls due to thermal movement and internal energy
Buoyancy is an upward force equal to the weight of the fluid displaced.
Hydrometers use this principle to measure relative density or specific gravity
Pascal's Law states pressure in a confined fluid transmits undiminished to all parts of the fluid and container
Pascal's law principle applies to hydraulic systems including mechanisms with increased mechanical Advantage.
Atmospheric pressure depends on the weight of the air above a given location, it is less dense at higher altitudes
Gauge pressure measures pressure relative to atmospheric pressure. Absolute pressure accounts for atmospheric pressure.
Differential pressure is the difference between two pressure levels; An aircraft wing experiencing varied pressure at differing altitudes.
Solids—have definite shape and volume; internal forces are strong
Fluids—both gases and liquids, and their force exerted is always perpendicular to surface and containments.
Gases—easily compressible; their volume changes with temperature/pressure.

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Test your knowledge on the properties and behaviors of gases and liquids in this quiz. Questions range from the characteristics that distinguish gases from liquids to how pressure interacts with both states of matter. Perfect for students of physical science!