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Engineering Senior Review > Unit 4 Topic 1 - Simple machines and mechanisms > Flashcards

Unit 4 Topic 1 - Simple machines and mechanisms Flashcards

1
Q

What are some examples of engineering disciplines which involve machines and/or mechanisms?

Provide examples of what they do?

A

Mechanical: Design power-producing machines, such as electric generators, internal combustion engines, and steam and gas turbines, as well as power-using machines, such as refrigeration and air-conditioning systems.

Mechatronic: Design and create control systems, robots, innovative machines and products that make people’s lives easier and their work more efficient.

Biomechanical: Study thermodynamics and other systems to solve biological or medical problems. Clinical engineers apply medical technology to improve healthcare.

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2
Q

What are some examples of real world basic machines? And what is the purpose of them?

A

Bicycle: To make transportation easier

Car Jack: Designed to lift a car/vechical off the ground

Crowbar: used as a lever either to force apart two objects or to remove nails

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3
Q

Name the four types of motion?

A
  • Linear
  • Rotary
  • Oscillatory
  • Reciprocal
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4
Q

What is Linear motion?
Provide some examples of things that travel in linear motion.

A

Is motion in a straight line; this line may be vertical or horizontal, may also be up or down an incline.

Cars, bikes, etc.

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5
Q

What is Rotary motion?
Provide some examples of things that travel in rotary motion.

A

Motion which is in a continuously circular path is rotary motion, that is, motion about an axis.

Spur gears, wheels, fan blades, Ferris wheels, merry-go-rounds, etc.

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6
Q

What is Oscillatory motion?
Provide some examples of things that travel in linear motion.

A

Oscillatory motion can be termed as the repeated motion in which an object repeats the same movement over and over.

In the absence of friction, the oscillatory motion would continue forever; but in the real world, the
system eventually settles into equilibrium.

Simple pendulum, vibrating strings of an instrument

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7
Q

What is Reciprocal motion?
Provide some examples of things that travel in linear motion.

A

Reciprocating motion is the repetitive back and forth, or up and down linear motion. Two motions that are opposite and contain a reciprocation cycle are
known as strokes. To convert a circular motion into a reciprocating motion, a crank is used.

Reciprocating pumps and engines, rack and pinion mechanisms, a table is moved up and down the central
pillar of a drill as a crank is turned.

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8
Q

Provide some examples of compond machines.

A
  1. The bell-crank mechanism
  2. Typical slider-crank mechanism
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9
Q

What is mechanical advantage?

A

Mechanism advantage occurs when a machine takes a small input force and increases the magnitude of the output force.

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10
Q

What is the mechanical advantage formula?

A

MA = load / effort = FL/FE

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11
Q

Define velocity ratio.

A

Is defined as the ratio of the distance moved by the point of application of the effort to the distance
moved by the load in a simple machine

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12
Q

What is the velocity ratio formula?

A

VR - distance moved by effort / distance moved by the load = dE/dL

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13
Q

What is efficiency?

A

Maximum productivity with minimal expenditure of effort; acting or producing effectively with a minimum of waste, expense or unnecessary effort.

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14
Q

What is the efficiency formula?

A

Efficiency GENERAL = Power(in) / Power(out)

Efficiency GEARS ONLY (n symbol) = MA / VR

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15
Q

What is a crow bar and how does it work?

A

Recognise: it is a first class lever

Describe: an iron or steel bar that is usually wedge-shaped at the working end for use as a pry or lever.

Purpose: to break apart concrete, pry apart wooden planks, to wedge under an object to move or lift it

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16
Q

What is a bicycle and how does it work?

A

Recognize: it is a complex machine made up of several mechanisms. Including wheels, axle, spokes, rim, tube, and tire), gears, chain, framework, crankshaft, bearings, pedals, brakes

Describe: A small, human-powered land vehicle with a seat, two wheels, two pedals, and a metal chain connected to cogs on the pedals and rear wheel. A frame gives the bike strength, and the other parts are attached to the frame.

Purpose: for transportation, fitness and fun

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17
Q

What is a car jack and how doe sit work?

A

Recognise: a car jack is a simple machine used as a lifting device to lift heavy
loads or to apply great forces.

Describe: is a tool that allows someone to lift a car off the ground in order to
make repairs or change a tire. An example of a car jack is the metal device
stored in the boot of your car.

Purpose: for lifting a car in order to work underneath it

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18
Q

What is a lever, and what are the different classes?

A

Levers are rigid bodies capable of rotating on a point on themselves to amplify an input force to provide a greater output force, which is said to provide leverage.
- First-class/order
- Second-class/order
- Third-class/order

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19
Q

What is a first-order lever? Provide an example.

A

Fulcrum between the effort and load.
- When the load moves more than the effort, 𝑀A > 1.
However, if the effort moves more than the load, 𝑀A < 1.

What do they do?
- Change the direction of the force
- Multiply effort force
- Magnify speed and distance

Examples
seesaw, scissors, crowbar

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20
Q

What is a second-order lever? Provide an example.

A

The LOAD is between the effort and the fulcrum.
- MA always greater than 1

What do they do?
- Multiply effort force
- MA greater than 1

Examples
Bottle opener, boat oars, wheel barrow

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21
Q

What is a third-order lever? Provide an example.

A

The EFFORT is between the load and the fulcrum.
- MA is always less than 1

What do they do?
- Magnify speed and distance

Examples
baseball bat, golf club, shovel

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22
Q

What is a gear? And what are they used for?

A

Gears are mechanisms that mesh together via teeth and are used to transmit rotary motion from one shaft to another.

Gears are defined by two important items: radius and number of teeth. They are typically mounted, or connected to other parts, via a shaft or base.

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23
Q

What is the mechanical advantage formula for Gears?

A

MA = torque_ driving / torque_ driven

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24
Q

What is the velocity ratio of gear formula?

A

VR = Driver/Driven

= speed_ driven/ speed_ driving

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25
Q

What are some types of gears? What are they and what do they do?

A

Spur: Are a type of cylinderical gear, with shafts that are parallel and coplanar, and teeth that are straight and printed parallel to the shafts.
- most common gear
- transmits power from one shat to another parallel shaft

Worm: are constructed of a worm and a gear, with non-parallel, non-intersecting shafts oriented 90 degrees to each other.

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26
Q

What are some types of gears? What are they and what do they do?

A

Spur: Are a type of cylinderical gear, with shafts that are parallel and coplanar, and teeth that are straight and printed parallel to the shafts.
- most common gear
- transmits power from one shat to another parallel shaft

Worm: are constructed of a worm and a gear, with non-parallel, non-intersecting shafts oriented 90 degrees to each other.
- The orientation of the worm and gear allows for
the transmission to be performed at a right angle.

Rack and pinion gear: ype of linear actuator that comprises a circular gear (the pinion)
engaging a linear gear (the rack), which operate to translate rotational motion into
linear motion. Driving the pinion into rotation causes the rack to be driven linearly

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27
Q

What is an incline plane?

A

Wedges and inclined planes make it easier to perform tasks by requiring less input force while producing greater
output force.

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28
Q

what is the mechanical advantage of an inclined plane?

A

An inclined plane’s mechanical advantage is the weight of the load to the force required to pull or push it up the ramp.

  • the MA of an inclined planed is described by the relationship between the length of the slope and the height of the inclined plane (while considering the efficiency of the system)

MA = F(load) / Force (effort)

29
Q

What is the velocity ratio of an inclined plane?

A

The VR of an inclined plane may be found by dividing the distance through which the effort moves by
the vertical distance through which the load is raised.

  • VR is calculated from its dimensions
  • as the verticle distance is always smaller than the distance moved by the effort, the VR is always greater than 1 for an inclined plane.

VR = Distance moved by effort / vertical distance moved by the load

30
Q

What is efficiency in relation to gears?

A

The efficiency, 𝜂, of a gear system is often used to determine the mechanical advantage of a gear system, and
hence torque of the driven gear:
𝜂 = MA/VR
∴ 𝑀A = 𝜂 × 𝑉R

31
Q

What is efficiency in relation to inclined planes?

A

The efficiency, 𝜂𝜂, of an inclined plane system is often used to determine the effort required to move a given load
and VR as:

𝜂 = MA/VR
∴ 𝑀A = 𝜂 × 𝑉R

32
Q

What is a screw?

A

Is a simple machine which works as a modified inclined plane. The thread of the screw can be
considered an inclined plane wrapped around the shaft of the screw

The slope of the screw is the distance for
one complete rotation while the height of the inclined plane is the distance between the threads, known as pitch

33
Q

What is the mechanical advantage in relation to a screw?

A

The MA is the relationship between the pitch and the circumference of the screw.

  • the closer the threads are, the GREATER the MA
  • it is easier to drive a screw into an object if the threads spacing is smaller (takes left effort but more turns)
  • & vice versa for if it had wider threads = harder to drill into the object but less turns
34
Q

What is the velocity ratio in relation to screws?

A

The velocity ratio per rotation of a screw can be found by using the formula for velocity ratio:
VR = distance moved by effort / distance moved by load
= dE/dL
= 2𝜋/pitch

35
Q

What is efficiency in relation to screw?

A

The efficiency, 𝜂𝜂, of a screw is often used to determine the load able to be moved with a given effort and VR as:

𝜂 = MA/VR
∴ 𝑀A = 𝜂 × 𝑉R

36
Q

What are a pulley and a pulley system? Provide a description and how they work.

A

Pulley = consists of a wheel and strong assembly.
- it is designed to lift heavy loads through comparatively lower magnitudes of effort.

DESCRIPTION: consists of two components, the wheel and the string; the wheel may be made up of
wood or metal and includes a grove cut along its circumferential periphery. The string is allowed to slide or pass
through this groove with a load that is to be lifted fixed at one of its ends and an effort applied at the other end in
order to lift the load. The pulley wheel is supported over a rigid frame about its central axis

37
Q

What is a first-order pulley? Provide a description.

A

A first-order pulley is a system made up of 2 or more pulleys.

  • the lowermost pulley here carries the load (being lifted)
38
Q

What is the MA of a first-order pulley system?

A

Mechanical advantage for a pulley system can be determined by the number of ropes involved in the effort of
raising the load and the efficiency of the pulley system.
𝑀A = load/effort = FL/FE

39
Q

What is the VR of a pulley system?

A

Velocity ratio of a pulley system can be found by also considering the number of ropes involved in the effort of
raising the load

VR = dE/ dL
= n

where n = number of ropes involved in the effort

40
Q

What is the efficiency of a pulley system (first order)?

A

The efficiency, 𝜂𝜂, of a pulley system can be calculated by the following formula, and it is commonly expressed as a
percentage:

𝜂 = 𝑀A / VR
OR
MA = 𝜂 X VR
OR
MA = 𝜂 X n

41
Q

What does kinemetaics mean?

A

Kinematics describe an objects motion by describing the when, where, how fast, how far and how long with asking why the objects moves in that certain way.

42
Q

What does dynamics mean?

A

Is the relationship between the motion of objects in our everyday world and the forces action on them

  • is the study of the CASUE in objects change in motion
43
Q

What is a force?

A
  • the measure of interaction between two objects (push or pull)
  • is a vector (magnitude and direction)
  • may be a contact force or a field force
44
Q

What is a contact force?

A

Contact forces result from physical contact between two objects.

45
Q

What is a field force?

A

Field forces act between disconnected objects.
- Also called “action at a distance.”

46
Q

What are the four things Forces can do, to an object?

A
  • accelerate the object
  • decelerate the object
  • change the direction of an object
  • change the shape of an object
47
Q

Define ENGERY (what is it?)

A

Energy is the ability to do work - to cause something to MOVE

  • energy can be found in serval forms, Chemical and Mechanical
  • use can get no more WORK out of a machine than the ENERGY you put into it
  • Measured in Joules
48
Q

Provide some forms of energy?

A

Solar, electrical, heat, light, chemical, mechanical, wind, water, muscles and nuclear

49
Q

What is the Law of Conservation of Energy?

A

States that energy can not be created or destroyed, only changed in form

50
Q

What is efficieny in relation to machines?

A

Is a measure of how much useful work a machine can do.

Efficieny = useful work output / work input

  • expressed as a %
51
Q

What are the THREE types of Energy? Also provide a definition.

A

Potential Energy - Energy of Position or stored energy

Kinetic Energy - Energy in motion

Mechanical Energy - the sum of potential and kinetic energy

52
Q

What is potential energy and how is it calculated?

A

Is Energy of Position or stored energy.

  • anything may have stored energy that gives it the potential to cause change if certain conditions are met.
  • The amount of potential energy that a sample of matter has depends on its position or condition
  • Potential energy is changed to Kinetic Energy upon movement.

PE = m x g x h
where; m = mass (kg)
g = gravity (9.8
m/s/s)
h = height (m)

53
Q

What is Kinetic Energy and how is it calculated?

A

Energy which a body possesses by virtue of being in motion.

KE = 1/2 m x v^2
where; m = mass (kg)
v = velocity (m/s)

54
Q

What is the energy conversation forumla?

A
  • when friction is small enough, and no mechanical energy is added to the system, then the system’s mechanical energy does not change.

Mechanical energy = KE + PE

55
Q

What is the WORK and whar is its forumal?

A

Work is the transfer of energy to an object when the object moves due to an application of a force

W = Fd (unit = Joules

56
Q

When is work done?

A
  • work is only done when the direction of the motion is in the direction of the force
    W = FxCos(theta)xd
57
Q

Different forces acting on the object? Why is it important in the WORK formula?

A

Fg = force due to gravity on an object - in this case, work is being done against or with the force of gravity

F = applied force = pushing or pulling the object

Ff = force of friction -> doing work AGAINST the applied force

58
Q

Why is the d important in the WORK formula?

A

The force must be in the direction of motion

59
Q

Provide an example of work?

A

• Example : carrying a box
- When carrying the box at constant height, work is done in direction of movement but not against gravity
- When the box is lifted, work is done against gravity
- When the box is dropped, work is done by gravity
- Comes in pairs: work is done by one force and against the other force in the pair

• Example : catching ball
- Move hand back when catching = smaller Force
- Work is still the same! (The ball has a certain KE which it has to dissipate in order to stop, v=0)
- Ball does work on hand
- More distance = more Work OR More Force = more Work

60
Q

Define power and its formula.

A

Power = the rate at which WORK is done

power = work (J) / time (s)

Unit = Watt (W)

P = work/time
= Fd/t
= Fv

  • Power is also change is energy over time:
    Power = Change in energy (J) / time (s)
61
Q

How is power loss and efficiency calculated?

A

Power loss = input power - output power

Power efficeny = output power/ input power X 100

62
Q

What are the quations of linear motion?

A

v = u + at
v^2 = u^2 + 2as
s = ut + 1/2 at^2

where: s = displacement
(m)
u = initial velocity
(m/s)
v = final velocity
(m/s)
a = acceleration
(m/s^2)
t = time (s)

63
Q

What is friction?

A

Is a force which opposes motion or the impending motion. Friction is the motion of one object moving relative to another.
- is a fundamental force

64
Q

What are the factors affecting friction?

A
  • friction depends on the smoothness of the contacting surfaces (friction only decrease with smoothness to a certain degree, friction actually increase between two extremely smooth surfaces)
  • friction depends on the magnitude of forces holding the bodies together
65
Q

What are the properties of frictional forces?

A
  • alwyas opposes motion
  • acts at right angles to the Normal force
  • proportional to Normal force
  • depends on the surfaces in contact
  • Kientic friction is less then Static friction
66
Q

What is the Ceofficent of Friction, µ?

A

Coefficient of friction, µ , is defined as a dimesionless number which is the ration between the friction force, Fr and the normal force, Fn

67
Q

What is the formal for Force due to friction?

A

The formula for the calculation of the force due to friction is :
𝐹𝑓 = 𝜇
Where: Ff = force due
to friction
μ = coefficient
of friction
N = normal force

68
Q

What is the Angle of repose?

A

Angle of repose, θ, is the angle that the plane of contact between two bodies makes with the horizontal when the
upper body is just on the point of sliding. It is the angle whose tangent is the coefficient of static friction between
the two bodies.

∴ 𝜇𝑠 = tanθ

Engineering Senior Review (4 decks)

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