Mechanics Flashcards
What is Newton’s first law of motion?
A body will remain at rest or continue to move with a uniform velocity unless acted upon by a force
What is the metric system unit of force?
Newtons
What is the imperial system for force?
Pounds
What is the equation of force?
Force= mass x acceleration
What is a moment?
A turning effect produced by a force
What is another way to describe mechanical advantage?
A moment
What is the equation for a moment?
Moment= force x perpendicular distance
What is the definition of a fulcrum?
The point at which you pivot against/around
What is a couple?
A pair of forces that are equal in magnitude and different in direction i.e when a aircraft rolls the forces on both ends of wings one is up and one is down
What is a resultant force?
The effect that results from two or more vectors acting on an object i.e two people pushing a box at 500N and 330N is a resultant of 880N
When would you use the triangle method (Pythagoras) to work out a resultant force?
When you have two forces acting with a 90° angle
What theorem does the triangle method use?
Pythagoras theorem
What is a scalar?
Are quantities that have magnitude but no direction i.e length, distance, speed
What is a vector?
They have a magnitude as well as direction in a straight line i.e velocity, acceleration, force and momentum
What is the abbreviation CG stand for?
Centre of gravity
What is the force of gravitational pull?
9.8 per m/s^2
When choosing a datum for the aircraft what is the only fixed rule to follow?
The datum must be positioned in a location that will not change during the life of the aircraft
How would you find the CG of an aircraft?
You would calculate the moments affecting all landing gear and add them together then simplify to get a distance
What happens to an aircraft before it leaves the production line?
It goes under structural testing
What is the definition of stress?
A quantity that describes the magnitude of forces that cause deformation
What is deformation also known as?
Strain
Stress is always accompanied by?
Strain
What is the unit for stress in the metric system?
Pascal or N/m^2
What is the unit for stress in the imperial system?
Pounds per square inch (Psi)
What is the equation for stress?
Force over area
What are the five basic structural stresses?
-tension
-compression
-shear
-bending
-torsion
What is the definition of strain?
The deformation of a material due to stress
Why does strain have no units?
Because its a ratio
What is the calculation for strain?
Change in length over original length
What is elasticity?
The ability of a material to return to its original shape once external forces are removed
What is the opposite to elasticity?
Plasticity
what is plasticity?
The ability of a material to change its shape permanently when its subjected to stress
What is tension?
When stress being applied tends to increase the length of the body
What is tension also known as?
-tensile stress
-axial stress
-normal stress
What is hooke’s law?
The extension of an elastic object is directionally proportional to the force applied to it
When does hooke’s law work?
When the elastic limit has not be exceeded
What is the elastic limit?
The point at which permanent deformation occurs and the elastic region ends
Once a material goes past the elastic limit what region does it enter?
The plastic region
When in the plastic region what becomes inproportional?
The force and deformation i.e small force means big deformation
What is compression?
The force which tends to shorten or squeeze a body
What is compression strength measured in?
N/m^2
What is shear stress?
When a body is being sliced by sliding one layer over another
What bolt is used to withstand shear loads?
Clevis bolts
What is bending?
When one side is under tension and the other side is being compressed
What is torsional stress?
When a material is being twisted
What two stress are found when a material is under torsion?
Tension and compression
At what angle does tension and compression work at when a material is under torsion?
Diagonally across the object
What is the definition of hardness?
The tendency to resist indentation or penetration of its surface i.e diamonds
What is the definition of strength?
The ability to withstand load without failure or plastic deformation i.e steel or titanium
What is the definition of toughness?
The tendency to resist breakage when deforming or when impact forces are applied i.e a hammer head or overcooked meat
What is brittleness?
The tendency to break without changing shape i.e glass or concrete
When do most materials get more brittle?
When cooled
What is elasticity?
The ability to return to its original shape when the force is removed i.e rubber bands
What is plasticity?
The tendency to remain in the new shape when the distorting force is removed i.e wet clay or play dough
What is the definition of malleability?
The ability to undergo compressive stress without damage i.e red hot steel
What is ductility?
The tendency to undergo tensile stress without damage i.e copper wire
What is the definition of fluid?
Any substance that flows (such as liquid, gases, and vapours)
What is the definition of vapour?
A gas that can be liquified by an increase in pressure without decreasing its temperature
What is the name for a gas when its below its boiling point?
A vapour
What is a volatile liquid?
When it readily evaporates at normal temperature with space above the surface
If you had a volatile liquid in a container with a open top, what would happen to the liquid?
It would evaporate until the liquid is gone
What is flammability?
When a material will catch on fire easily
Vapours given off by volatile liquids are?
Highly flammable
Flammable and inflammable are synonyms but which is preferred?
Flammable
What is flash point?
The temperature at which something will catch fire when exposed to a naked flame
When a substance has a lower flash point is it easier or harder to ignite the material?
Easier
What is toxicity of substance?
It refers to how poisonous it is
Common signs of being around toxic substances?
Skin irritations, soreness in the eyes, feeling sick, and difficulty in breathing
What is the definition of inert?
Any substance that will not chemically combine with another substance
All inert substances are?
Gases
What is the calculation for pressure?
Pressure = force over area
How do you calculate area?
πr^2
What is atmospheric pressure?
The force exerted by the weight of the atmosphere
The density of air varies when what change?
Altitude
At sea level what is the average atmospheric pressure?
14.7psi
What is the most common barometer?
Mercury barometer
What is used to measure atmospheric pressure?
Barometers
If atmospheric pressure is 14.7 psi what is it in bar?
1.01 bar
How does a mercury barometer work?
A vertical glass tube is placed sitting on top of a mercury bath and when the pressure increase more mercury is sucked up
What is gauge pressure?
The difference between the pressure inside a body and the pressure outside
What is absolute pressure?
The difference between the pressure inside a body and zero pressure
What is archimedes principle on buoyancy?
That a body in a fluid will be subject to an upward force equal to the weight of fluid it displaces
When does neutral buoyancy occur?
When an objects weight is equal to the weight of the fluid displaced
What are the 3 simple stresses?
-tension
-compression
-shear
What is the definition of a combined stress ?
When an object is affected by more than one type of stress at a time
What is motion?
A continuing change of position
If a object is in motion and if the distance the object moves remains the same it is said to be?
Uniform
What is velocity?
The change in displacement over time
If a objects velocity is not constant, it is said to be?
Accelerating
What is the equation for acceleration?
Change in velocity over time
Why is velocity a vector quantity?
Because it has a direction
Why is speed a scalar quantity?
Because it doesn’t have a direction
If there is two objects traveling at 10m/s in opposite directions have the same speed But different?
Velocities
Why is it possible for an object to change in acceleration but not speed?
Because acceleration is the change of speed, direction, or both
How do you calculate acceleration?
(Initial velocity^2 minus final velocity^2) over 2 times displacement
When is the only time acceleration remains constant?
When the acceleration is caused by earths gravitational pull
If a stone is dropped from a tower and takes 4 seconds to reach the ground, what is the velocity at impact?
Initial+gravity x time
0+9.8 x 4 =39.2
If a satellite is orbiting earth at a constant speed, is its velocity changing?
Yes because its changing direction constantly
What is centripetal force?
The force required to cause acceleration towards the centre of rotation
What is Newton’s first law?
An object at rest remains at rest, and an object in motion remains in motion unless acted on by an unbalanced force
What is the equation for centripetal force?
Mass x velocity^2 over radius
What is centripetal acceleration?
The acceleration experienced while in uniform circular motion
What direction does centripetal acceleration act?
Towards the centre of rotation
What is centrifugal force?
A fictitious force from being opposite to centripetal force
In relation to pendulums what is angular amplitude?
Angular displacement from rest to maximum swing position
In relation to pendulums what is a oscillation?
One complete swing to and from maximum position
What is meant by the ‘length of pendulum’?
Distance from the pivot to the centre of gravity of the bob
In relation to pendulums what is periodic time?
Time taken to complete one oscillation
In relation to pendulums what is one cycle?
The motion completed in one period
In relation to pendulums what is frequency?
Number of cycles completed in a unit of time
In a pendulum does the mass of the bob have an effect on the periodic time?
No
Periodic time of a pendulum increase when?
Pendulum length increases or gravity decreases
What is damping?
Is a decrease of vibrations as a result of removing energy through resistance to motion
What is vibration?
Mechanical oscillations about an equilibrium
How are sound and pressure waves generated?
By vibrating structures
What is free vibration?
When a mechanical input has an initial input and then its allowed to vibrate freely until it dampens out
What is forced vibration?
When continuous force or motion is applied to a mechanical system
What is a periodic vibration?
A vibration that repeats itself at standard intervals i.e harmonics
On a harmonic graph what does the bottom number indicate?
The amount of waves there are in one time interval
What is resonance?
The tendency of a system to oscillate at maximum amplitude at a certain frequency
If a vibration isn’t in resonance what will happen?
It will never get big as it will act as a natural dampener
What is velocity ratio?
How far the effort has to move in relation to the load
What are the units for velocity ratio?
There isn’t any units as its a ratio
What is mechanical advantage?
The ratio of force produced by a machine to the force applied to it
What are the units for mechanical advantage?
There isn’t any units as its a ratio
What are the three types of lever?
-first class lever
-second class lever
-third class lever
In a first class lever where is the fulcrum positioned?
Between the effort and the resistance (normally In the middle)
What are some examples of a first class lever?
Seesaw, crowbar, pliers
What is the equation for mechanical advantage?
Resistance over effort
What is the equation for mechanical advantage of a lever?
Effort x length of effort arm = resistance x length of resistance arm
What is a second class lever?
When the fulcrum is at one end of the lever and the effort is applied to the opposite end i.e wheelbarrow
What is a third class lever?
When the fulcrum is at one end and the resistance is at the opposite end with the effort somewhere between them i.e landing gear
In relation to mechanical advantage, What is an incline plane?
A plane surface inclined to a horizontal plane at any angle but a right angle i.e luggage conveyor
What is a pulley?
A wheel or set of wheels which a rapper or chain is pulled in order to lift or lower objects
Is there any mechanical advantage in a single stationary pulley?
No
If a single pulley is not fixed and the effort and weight move in the same direction, do you gain mechanical advantage?
Yes
How do you gain mechanical advantage by using gears?
By varying the teeth ratio on the gears
If both the drive gear and driven gear have the same number of teeth do you have mechanical advantage?
No its the same
If the drive gear and the driven gear have different number of teeth do you have mechanical advantage?
Yes it can be more than or less than 1
What is the equation for mechanical advantage of gears?
Driven over drive
If you had a drive gear of 20 teeth and a driven gear of 40 teeth, what would the mechanical advantage be?
2
What is torque proportional to?
Horsepower
What is a spur gear?
When their teeth are cut straight across their circumference (look like spurs) i.e normal gears
If you had two spur gears with external teeth connected together which way would the driven gear turn?
The opposite to the drive gear
If you wanted two spur gears to turn in the same direction what would you need?
One gear to have an internal thread
What is a bevel gear?
When the teeth are cut into a conical surface
When would you use a bevel gear?
To transmit power between two shafts at an angle to each other
What angle can bevel gears work up to?
Any less than 180˚ but typically used at 90˚
The teeth on a bevel gear are external, what direction will the driven gear turn?
The opposite
What is a worm gear?
A toothed wheel turning a revolving cylinder with a screw thread
In a worm gear what is the driving component?
The cylinder (the worm)
When is a worm gear used?
A large reduction in speed or high torque multiplication
What are the difference peices in a sun and planet gear?
-sun gear
-planet gear
-ring gear
-a cage
In the sun and planet gear what gear is the input?
The sun gear
What is the output in a sun and planet gear?
The cage
Why are sun and planet gears used?
When there is limited space and a need for a large reduction in speed and torque
What is efficiency?
The ratio of work which is transferred to a useful form compared to the total input work
What is efficiency measured in?
Percentage
Why cant machines be 100% efficient?
Due to the losses like heat, friction, deflection, as well as wear and tear
What is Isaac Newton’s first law of motion?
Every object remains in its state of rest or in uniform motion in a straight line, unless it is made to change by external forces impressing on it
What is Isaac Newton’s second law of motion?
The acceleration of an object produced by a force is directly proportional to the force, is in the same direction as the force, and is inversely proportional to the mass of the object
What is Isaac Newton’s third law of motion?
Every action has an equal and opposite reaction
What is the equation for force?
Force = mass x acceleration
What is Newton’s third law of motion sometimes referred to?
The law of action and reaction
What is the definition of mass?
The amount of matter in a body regardless of its volume or position
What is an atomic mass unit?
The mass of a proton or neutron
What is the equation for mass?
Mass = weight / gravitational acceleration
What is the unit for mass?
Kilograms
What is the definition of weight?
The gravitational force of attraction between the mass of the earth and the mass of a body
What is the unit of weight?
Newtons or pounds
Will the weight of a body increase, decrease or stay the same as it moves away from the earths centre?
It will decrease as gravity is getting lower
What is the equation for weight?
Weight = mass x gravity
What is inertia?
The property of matter that causes it to resist any change to is motion
What does the amount of inertia depend on?
The amount of mass
What is the definition of work?
The force causing a movement or a displacement of an object
What is the equation for work?
Work = force x distance moved
In the scientific sense if someone was holding a pile f books is work being done?
No because there is no movement
What is work measured in?
Joules
One joule is equal to?
One Newton meter
What is the definition of power?
A measurement of the rate which work is done or at which energy is converted from one form to another
What is the equation for power?
Power = work / time
What is the unit for power?
Watt
One watt is equal to?
One joule per second
What is energy?
The capacity to do work
What is mechanical energy?
The energy held by a body after work has been done
What are the different types of energy?
-potential energy
-kinetic energy
-total energy
-chemical energy
-heat energy
What is potential energy?
When a body has energy due to its position or condition
What is the equation for gravitational potential energy?
Mass x gravity x height
What is kinetic energy?
Energy a body has due to its motion
What is the equation for kinetic energy?
½ x mass x velocity^2
What is total energy?
The sum of all different forms of energy in a system
Can energy be created or destroyed?
No but it can be converted
What is chemical energy?
The energy which is stored in the chemical bonds between atoms
Chemical energy is a form of what other energy?
Potential energy
What is heat energy?
The energy which a body possesses due to the kinetic energy and the potential energy of its molecules
Thermal energy is also called?
Internal energy
When converting energy from one form to another what is the common by product?
Heat
What is the equation for efficiency?
(Useful energy / total energy) x 100
What is momentum?
A vector quantity that describes mass in motion
The more momentum something has the harder it is to?
Stop
An objects momentum depends on what two variables?
Mass and velocity
The direction of the momentum vector is the same as?
The velocity
What is the equation of momentum?
Mass x velocity
What is the definition of a collision?
When two objects interact with one another, leading to transfer of kinetic energy and momentum
What are the two types of collisions?
Elastic Collisions and in elastic collisions
What are elastic collisions?
When two objects collide and bounce of each other to travel in opposite directions i.e newtons cradle
What is an inelastic collision?
When two objects collide and merge together to travel in the same direction i.e a car crash
What are the 3 key facts to an elastic collision?
-No loss of kinetic energy or momentum
-no heat exchange
-no damage
What are the 4 key factors to elastic collisions?
-no loss of momentum
-kinetic energy lost
-heat created
-damage to objects
What is the conservation of momentum equation?
M1u1+M2u2 = M1v1+M2v2
What is a gyroscope / gyro?
An instrument that contains a disc that rotates about an axis at a high speed
In a gyroscope what is the disc sometimes called?
A rotor
What are the two important properties of a gyroscope?
Rigidity and precession
What are the 4 factors that affect a gyroscope?
-rotor mass
-radius at which the mass acts
-speed of rotation
-bearing friction
If you were to apply external force to change the direction of the rotor spin axis of a gyroscope what would happen?
The gyro resists the change and moves the force at right angles to the direction originally applied
Why are gyros used to maintain orientation of an aircraft in flight?
Because once spinning they aren’t affected by the aircraft manoeuvres
What is friction?
The force resisting the relative motion of materials rubbing against each other
In relation to friction, When on horizontal surfaces what does the normal force become equal to?
The objects weight
What is starting friction?
The friction as soon as the object starts to move
What is starting friction sometimes refereed to as?
Break away force
Does an object slide easier, harder, or same after the starting friction?
Easier due to momentum
What is sliding friction?
The friction of two objects after the initial starting friction
What does the amount of sliding friction depend on?
The nature of the material surfaces
What is rolling friction?
Friction between a rolling body and the surface on which it rolls
Which direction does friction go compared to the force applied to the object?
The opposite
What are the effects between surfaces that are under friction?
Damage and an increase in heat
Why is sliding fiction less than starting friction?
Because the force needed to start a body sliding is greater than the force to keep a body sliding
Why is weight measured in newtons?
Because its a force
What is impulse force?
A force applied over time
What is the equation for density?
Density = mass / volume
Although the standard unit for mass is kilograms (kg) and for volume is cubic metres (m^3), what is the norm units for a laboratory situation?
mass in grams (g) and volume in cubic centimetres (cm^3)
If you wanted to convert from kg/m^3 to g/cm^3 what would you do?
Divide by 1,000
If you wanted to convert from g/cm^3 to kg/m^3 what would you do?
Multiply by 1,000
What is specific gravity (SG) sometimes referred to as?
Relative density
What is used to compare the densities of two substances?
Specific gravity
Densities of all liquids and solids are compared by using water at what temperature?
4˚C
Densities of gases are compared by using air at what temperature?
Room temperature (20˚C or 68˚F)
What is a hydrometer used for?
To determine the specific gravity of an electrolyte (battery liquid)
What is viscosity?
The resistance of a fluid to a change in shape or relative movement
What causes a fluid to have a high viscosity?
By internal friction between molecules
If the temperature increases what happens to the viscosity of a liquid?
It decreases (becomes more runny)
When temperature increases what happens to the viscosity of a gas?
It increases (more thick)
What is fluid resistance / fluid friction?
When a solid object travels through a liquid or gas or indeed when a liquid or a gas travels through a solid
What are the determining factors for fluid resistance/ fluid friction?
-viscosity of fluid
-surface texture
-shape of the object
What is streamlining?
Decreasing the amount of restrictive force of fluid friction
In relation to to streamlining why are composites used?
Reduces the need for riveting which makes it more efficient
Under standard ISA conditions what is the speed of sound at sea level? (International standard atmosphere)
340m/s
When airflow is faster than the speed of sound what is created?
A shock wave
An increase in liquid pressure will have what affect on the liquid?
Increase the liquid internal temperature and reduce its viscosity
What is the equation for pressure?
Pressure= force / area
If you had three different sized water containers 10m^2, 100m^2, 150m^2, would the water pressure be the same at 3m?
Yes because water pressure only increases with depth
If pressure is force over area, what is the equation for force?
Area x pressure
If you had a piston with 1000 psi applied to both ends what would happen?
The piston would move to the rod end due to having a smaller surface area due to the rod taking up space
What is static pressure?
The sum of gravity, applied force, and atmospheric pressure
What is dynamic pressure?
The pressure that emerges from velocity of the fluid in motion
What is total pressure?
The sum of static and dynamic pressure
When flow velocity of a liquid increase what happens to the pressure?
Static pressure decreases and dynamic pressure increases
What is pressure energy?
Energy stored in a fluid due to the force per area applied to it
What is the equation for pressure energy?
Mass x pressure /density of fluid
What is the equation of lift?
Lift = difference in pressure x area of wing
According to pascals law what angle does pressure act at to the container?
90°
Pascals law states that pressure is ——— throughout the enclosed liquid
Equal
