Physics Class: Force and Its Effects
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Questions and Answers

A container is filled with different liquids. Which property determines whether a liquid will float on top of another?

  • The total mass of each liquid.
  • Density of the liquid relative to others. (correct)
  • Volume of the liquid.
  • The shape of the container.

    • Why are liquids considered incompressible, unlike gases?

  • Liquids have a constant density. (correct)
  • Liquids follow Pascal's Law, while gases do not.
  • Liquids do not exert pressure.
  • Liquids have a variable density.

    • A submarine is submerged at a certain depth in the ocean. If the submarine dives deeper, what happens to the pressure exerted on it?

  • The pressure increases due to the greater height of the water column above. (correct)
  • The pressure remains the same because the volume doesn't change.
  • The pressure decreases because water is incompressible.
  • The pressure fluctuates randomly.

    • A hydraulic jack uses Pascal's Law to lift heavy objects. If the input force is applied over a small area, how is a larger output force generated?

    <p>By applying the pressure over a larger area. (D)</p> Signup and view all the answers

    An object is submerged in water. According to Archimedes' principle, what determines the buoyant force acting on the object?

    <p>The weight of the water displaced by the object. (B)</p> Signup and view all the answers

    An irregularly shaped solid is suspended from two different points. What does the intersection of the vertical lines passing through these points represent?

    <p>The center of gravity (CG) of the solid. (B)</p> Signup and view all the answers

    A metal rod fixed at one end is subjected to a twisting force. What type of stress develops within the rod as a result?

    <p>Shear stress, with compression in the direction of the twist and tension in the opposite direction. (D)</p> Signup and view all the answers

    An aircraft wing experiences alternating compression and tensile stresses on its top and bottom surfaces during flight. What is the primary cause of these stresses?

    <p>Aerodynamic and gravitational forces bending the wing. (C)</p> Signup and view all the answers

    When does shear stress occur?

    <p>When external forces distort a body so that adjacent layers of material tend to slide over one another. (C)</p> Signup and view all the answers

    A component fails in service despite low externally applied stress levels. What could be a contributing factor to this failure?

    <p>Presence of residual stresses from manufacturing processes. (D)</p> Signup and view all the answers

    A force is applied to an object. Which of the following outcomes indicates that the applied force has done work on the object?

    <p>The object starts moving and gains kinetic energy. (A)</p> Signup and view all the answers

    In a balanced lever system, what principle must be observed regarding the moments on either side of the fulcrum?

    <p>The load moment and the effort moment must be equal. (D)</p> Signup and view all the answers

    A mechanic uses a crowbar to lift a heavy crate. In this scenario, the crowbar acts as a first-class lever. What is the defining characteristic of a first-class lever?

    <p>The fulcrum is situated between the effort and the load. (C)</p> Signup and view all the answers

    An aircraft cockpit throttle lever is an example of a second-class lever. What is the arrangement of the fulcrum, load, and effort in a second-class lever?

    <p>The load is between the fulcrum and the effort. (A)</p> Signup and view all the answers

    An aircraft landing gear retraction mechanism exemplifies a third-class lever. What distinguishes a third-class lever from other classes of levers?

    <p>The effort is located between the fulcrum and the load. (B)</p> Signup and view all the answers

    In a pulley system with a mechanical advantage (MA) of 4, an operator pulls a rope a distance of 1 meter. How far is the load raised?

    <p>0.25 meters (D)</p> Signup and view all the answers

    What distinguishes a 'couple' in mechanics from other force systems?

    <p>A couple consists of two equal and parallel forces acting in opposite directions at different points on a body. (A)</p> Signup and view all the answers

    How is the center of gravity (CG) of a regularly shaped object with uniform density typically determined?

    <p>By identifying the geometric center of the object. (D)</p> Signup and view all the answers

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    Flashcards

    Stress

    Force acting through a section of solid material, defined as force per unit area.

    Strain

    Deformation of a material as a result of stress; proportional to stress below elastic limit.

    Elastic Limit

    The maximum stress a material can withstand without permanent deformation.

    Tension

    Forces that tend to pull an object apart, like in cables or wires.

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    Torsion

    A type of shear stress occurring due to twisting forces on a fixed object.

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    Force

    A push or pull capable of changing a body's state of motion.

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    Equilibrium

    A state where the resultant force on an object is zero, indicating no change in motion.

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    Lever

    A simple machine that uses a fulcrum to amplify effort to lift a load.

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    Mechanical Advantage (MA)

    The ratio of load lifted to the effort applied in a machine.

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    Velocity Ratio

    The direct ratio of the speeds of two points in the same system.

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    Couple

    Two equal forces acting in parallel but opposite directions on a body.

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    Centre of Gravity (CG)

    The point where the weight of a body appears to act.

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    Moment

    The force multiplied by the perpendicular distance from the fulcrum.

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    Buoyancy

    The upward force that supports an object in a fluid, equal to the weight of the displaced fluid.

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    Pressure

    Force applied per unit area, often caused by molecules in a fluid hitting a surface.

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    Specific Gravity

    The ratio of a substance's density to the density of water, indicating if it will float.

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    Archimedes' Principle

    States that an object submerged in fluid displaces a volume of fluid equal to its own volume.

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    Pascal's Law

    When pressure is applied to a confined fluid, it exerts equal pressure in all directions.

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    Study Notes

    Force and its effects

    • Force causes a change in a body's state of motion
    • Force application can: start, stop, accelerate or decelerate a mass
    • Work can be performed if energy is available

    Work and Resultant Force

    • Forces can act in different directions
    • Resultant force is calculated by resolving individual forces
    • Equilibrium occurs when the resultant force on an object is zero; the object is not changing its state of motion or rest

    Moments and Levers

    • Moment is the force multiplied by the distance from the pivot point (fulcrum)
    • Lever system is balanced when load moment equals effort moment
    • Increasing effort force raises the load
    • Lever is a simple machine providing mechanical advantage (MA)
    • MA= Load/Effort
    • Levers are used to perform work, moving a load with an effort, pivatig around a fulcrum.
    • First-class levers example: crowbar
    • Second-class levers example: cockpit control levers, wheelbarrow

    Third-Class Lever

    • Effort is between the fulcrum and the load,
    • Example: retraction mechanism on an aircraft landing gear

    Velocity Ratio

    • Velocity Ratio (VR) is the direct ratio of two speeds in the same system
    • Example: pulley system with 4 MA, rope moves 4 times faster than load is raised

    Couples

    • Couple is a moment derived from two equal forces acting in parallel but opposite directions on two different points of a body
    • Produces a torque, or twisting force on a body

    Centre of Gravity (CG)

    • CG is the point where the weight of a body appears to act
    • CG is the geometric centre of uniformly dense bodies
    • CG of irregularly shaped objects is the intersection of verticals passing through different suspension points

    Stress, Strain, and Elasticity

    • Stress is the force acting through a section of a solid material, defined as force per unit area.
    • Strain shows deformation of material due to stress
    • Elasticity allows a material to return to its original shape below the elastic limit.
    • Hooke's Law states stress and strain are proportional below elastic limit: doubling stress doubles strain.

    Tension

    • Tension describes forces that pull apart an object
    • Example: steel cable in aircraft control systems

    Compression

    • Compression is the resistance to pushing a body together.
    • Example: weight of an aircraft compressing runway, rivets.

    Shear

    • Shear stress occurs when external forces cause adjacent layers to slide over each other.
    • Example: oil or grease on sliding metal surfaces

    Torsional Stress

    • Torsion or torque is a form of shear stress caused by twisting force
    • Fixed at one end, material sections slide over each other
    • Twisting results in compression stress in one direction and tension stress in opposing direction.

    Residual stress

    • Abrupt or uneven temperature changes cause internal stress (common in heat-treating metals)
    • Can lead to component failure, even with low external stress.

    Pressure and Buoyancy

    • Liquids and gases are fluids
    • Liquids are incompressible; gases are compressible
    • Pressure is force per unit area
    • Pressure in fluids is due to molecules bombarding container walls.
    • Pressure from a fluid column depends on height, gravity, and fluid density.
    • Archimedes' principle: an object immersed in fluid displaces equal volume of fluid, buoyed up to weight of displaced fluid.
    • Floating if buoyant force is greater than weight

    Density and Specific Gravity

    • Density is mass per unit volume
    • Specific gravity is a substance's density compared to water.
    • Gasoline's specific gravity is .72; meaning weight is 72% of the same amount of water
    • Gases compared to air yield SG.

    Solids, Liquids, and Gases

    • Solids have definite shape and volume, with strong interatomic forces

    • Liquids have definite volume, but take shape of container

    • Gases take both volume and shape of container; comparatively easy to compress.

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    Description

    Test your understanding of force, work, and the principles of levers in this quiz. Explore how forces affect motion, the concept of resultant force, and the mechanics of different types of levers. Challenge yourself with questions on moments and their calculation, as well as practical applications of levers.

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