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Industrial Mechanic/Millwright > Trade Science > Flashcards

Trade Science Flashcards

1
Q

Why does a millwright need to understand trade sciences?

A
  • The millwright trade is based on applied scientific principles.
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2
Q

Define atoms and molocules.

A
  • Atoms are single units of special substances called elements.
  • Atoms or elements unite to form more complex structures called molecules.
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3
Q

Define compounds and mixtures.

A
  • A compound is the product of two or more atoms that unite chemically, this creates a substance that has properties different from those of the combining elements.
  • Two or more elements or compounds may combine so that the molecules in the resulting material retain their original properties, this is called a mixture.
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4
Q

Is brass a mixture or a compound?

A
  • Mixture
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5
Q

What are the physical states of matter?

A
  • Solid, liquid or a gas
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6
Q

Can all forms of matter be changed from one physical state to another and then returned to its original state?

A
  • No
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7
Q

Define cohesive forces and adhesive forces.

A
  • Molecules in a solid are strongly attracted to one another and this attraction is called cohesive force, it limits the space around individual molecules, packing them relatively closely so solids hold definite shapes.
  • Molecules that are not alike often share a force of attraction similar to cohesion, this intermolecular force is called adhesive force.
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8
Q

Define mass and weight of an object.

A
  • Mass is the measurement of the quantity of material in a body.
  • The force of gravity on Earth determines what most of us call weight, when you measure the weight of an object you measure the force of gravity acting on it. The weight is proportional to mass.
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9
Q

Define volume.

A
  • Volume is a measurement of the amount of space an object occupies.
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10
Q

Define density.

A
  • Density indicates the mass of a body in a given volume.
  • Density is the ratio of a mass to a volume.
  • Density - mass / volume
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11
Q

What are the reference materials for specific gravity of?

(a) solids and liquids
(b) gases

A
  • (a) water

- (b) air

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12
Q

What are the main characteristics of a solid?

A
  • Solids maintain there own shape without a container.
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13
Q

Define ultimate strength.

A
  • Strength is the ability to withstand gradually applied forces without rupturing, these forces may be tensile, compressive, or shear.
  • The point at which the material ruptures is known as its ultimate strength.
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14
Q

Define stress and strain.

A
  • Stress is defines as the force per unit area acting on an object to change its dimensions.
  • Stress = Force x Area
  • Strain is the ratio of the extension per unit length when force is applied.
  • Strain = Extension / Original Length
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15
Q

Define tensile strength.

A
  • Tensile strength is the ability of a material to resist being pulled apart by external forces
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16
Q

Define compressive strength.

A
  • Compressive strength is the ability to resist external forces that push into or against the material.
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17
Q

Define shear strength.

A
  • Shear strength is the ability to resist forces that try to slide part of the object along itself.
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18
Q

Define fatigue strength.

A
  • Fatigue strength is the ability to withstand repeatedly alternating stresses.
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19
Q

Define elasticity.

A
  • Elasticity is the ability of a material to return to its original dimensions after it has been acted on by a force.
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20
Q

Define elastic limit or yield strength.

A
  • The maximum force that a solid can withstand without being permanently deformed is called the materials elastic limit or yield strength.
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21
Q

Define placticity.

A
  • Plasticity is the ability for a material to retain a shape permanently after a deforming force is removed.
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22
Q

Define ductility.

A
  • Ductility is the ability to stretch and maintain a new shape.
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23
Q

Define malleability.

A
  • Malleability is the ability of a material to be permanently deformed by compression forces.
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24
Q

Define brittleness.

A
  • Brittleness breaks without noticeable plastic deformation, brittleness is the absence of malleability.
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25
Q

Define toughness.

A
  • Toughness is the ability of a material to withstand shock loads.
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26
Q

Define hardness.

A
  • Hardness is a materials ability to resist a force that is trying to penetrate it.
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27
Q

What are the physical properties of solids?

A
  • Physical properties of solids are the characteristics of their interaction with various forms of energy.
  • Electrical conductivity.
  • Thermal conductivity.
  • Expansion and contraction.
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28
Q

What are the chemical properties of solids?

A
  • Composition
  • Corrosion Resistance
  • Electrochemical reaction (electrolysis)
29
Q

What affect does electrolysis have on metals?

A
  • When two different metals are in contact with one another and water is present, an electric current is produced. The electron flow has a chemical effect, corroding metals.
30
Q

What is the galvanic series with regard to metals?

A
  • In the galvanic series, each metal is corroded by all the metals listed after it.
  • aluminum
  • magnesium
  • chromium
  • iron or steel
  • cast iron
  • cadmium
  • nickel
  • tin
  • lead
  • brass
  • copper
  • bronze
  • copper-nickel
  • silver
  • platinum
  • gold
31
Q

Describe the properties of liquids.

A
  • Liquids are nearly incompressible. They have no defined shape, but take the shape of their container.
  • Cohesive forces hold a liquid together and adhesive forces allow liquids to adhere to surfaces.
  • Volatility is a measure of how quickly a liquid vaporizes.
  • Viscosity is a measure of a liquids resistance to flow.
32
Q

Describe the properties of gases and compare them to the properties of liquids.

A
  • Gas molecules are widely spaced and can act independently, moving freely. Gases can expand or be compressed into any space regardless of size.
  • Many of the principles of liquids also apply to gasses. They are often studied together under the general heading of fluids.
  • The main difference between gases and liquids are in compressibility and elasticity. Gases are highly compressible and very elastic.
  • When a gas is compressed its volume is reduced. It is said to be under pressure. The gas molecules become tightly packed and the compression increases the number of moving particles that strike the sides of the confining container.
33
Q

How is the pressure of gas measured?

A
  • Pascal (Pa), Kilopascal(kPa) and pounds force per square inch (lbf/in2 or psi).
  • Gas pressure may be measured by means of a gauge.
  • 1 Atmosphere = 101.35 kPa = approx. 1 bar = 14.7 psi
34
Q

Describe internal energy.

A
  • In most conditions, a material’s molecules are in constant, random motion. This molecular movement is an energy form called thermal energy, or, more correctly, internal energy.
  • If a hotter object comes into contact with a cooler object, the more energetic molecules of the hotter object transfer some of their internal energy to the cooler object. They do this by colliding with the less energetic molecules.
35
Q

Define heat.

A
  • Heat is energy in transit from a body at a higher temperature to a body at a lower temperature.
36
Q

Name the instruments used to measure temperature .

A
  • Liquid expansion thermometer. A change in temperature changes the volume of the fluid.
  • The bi-metallic strip thermometer, has a strip of two different metals bonded together. This strip may be bent into a coil and linked to a pointer. The two metals expand at different amounts causing the pointer to tighten or unwind.
  • Pyrometers. Optical pyrometers measure the temperature by observation of the color produced by the object being heated. Thermoelectric pyrometers are resistance thermometers. As their temperature changes, electrical conductors change their resistance to the flow of electrical current.
  • Thermocouples consist of an electrical circuit terminating with the junction of two different metals. When the temperature of the junction is raised, a voltage is produced across the junction.
37
Q

Define a British thermal unit.

A
  • A British thermal unit is the amount of heat needed to change the temperature of 1 lb of water by 1 degree Fahrenheit .
38
Q

How many British thermal units in a kilojoule?

A
  • 1 kJ = 0.948 Btu
39
Q

Define thermal expansion.

A
  • If it free to move, almost all matter expands when heated. This is called thermal expansion.
40
Q

Define linear expansion.

A
  • Linear expansion refers to a change in the dimension of an object in a particular direction: length, width, height or diameter.
41
Q

Define coefficient of linear expansion.

A
  • The different rates of linear expansion of various materials are expressed as coefficients of linear expansion.
42
Q

Define volume expansion.

A
  • A heated substance expands in all directions. That is, the volume of the heated material expands with a change in temperature.
43
Q

Define coefficient of volume expansion.

A
  • The coefficient of volume expansion is three times the coefficient of linear expansion.
44
Q

Describe how heat is transferred by conduction, convection and radiation.

A
  • When heat is transferred by conduction, the heat travels directly through a material.
  • The upward movement of a less dense fluid coupled with the downward movement of a denser fluid is called convection.
  • Heat transfer is similar to light and may occur through space in the same way. The special waves produced by thermal radiation are emitted by an object because of its temperature. Heat transfer of this type is called radiant heat.
45
Q

Define thermal conductivity.

A
  • A materials ability to conduct heat is called the materials thermal conductivity. Heat transfers from areas of higher temperatures to areas of lower temperatures.
46
Q

Define force.

A

Forces is defined as an external agent that causes a change in motion or stress in a body.

47
Q

State Newton’s first, second and third laws of motion.

A
  • A body at rest will stay at rest and a body in motion will remain in motion at the same speed ad in the same direction unless acted on by some other force.
  • A force acts on a mass to cause acceleration. The size of a net force (F) on an object is equal to the product of the mass (m) and acceleration (a) of the object. F = m x a
  • For every action, there is an equal and opposite reaction.
48
Q

Define velocity.

A
  • Velocity is the distance a body moves in one direction per unit time.
  • velocity = distance / time
49
Q

Define speed.

A
  • Speed is velocity without direction.
50
Q

Define acceleration.

A
  • If velocity or speed changes, we say that the movement is accelerated or decelerated.
  • acceleration = (final velocity - original velocity) / time
51
Q

How are rotary motion and periphery speed expressed?

A
  • Rotational motion occurs when a force causes an object to rotate around an axis. Expressed in revolution per minute, RPM.
  • The periphery (outside edge) of a rotating object moves at a particular velocity. Expressed as meters per minute or surface feet per minute/feet per minute.
52
Q

List three classifications of energy.

A
  • Potential (static)
  • Kinetic (dynamic)
  • Radiant (electromagnetic)
53
Q

What does the law of conservation of energy state?

A
  • Energy cannot be created or destroyed, but it may be converted from one form to another.
54
Q

Define work.

A
  • The work (W) done on an object equals the force (F) applied to the object times the distance (d) that the object moves in the direction of that force.
  • W = force x distance
  • Work is done whenever one kind of energy is converted to another type of energy.
55
Q

List and describe the units used to measure work.

A
  • 1 joule (J) is the work done by a force of 1 Newton (N) over a distance of 1 meter (m).
  • 1 foot-pounds-force (ft.lbf) is the work done by a force of 1 lbf acting over a distance of 1 foot (ft).
56
Q

Define power.

A
  • Power is the rate at which work is done.

- Power = work / time

57
Q

List and describe the units used to measure power.

A
  • Metric units are watts (W)
  • 1 W = 1 Joule per second
  • Imperial units are horsepower (HP)
  • 1 hp = 550 ft.lbs per second
58
Q

Define mechanical advantage.

A
  • Mechanical advantage is the ratio of work done to the effort required.
59
Q

Define efficiancy.

A
  • When work is done with very little loss of energy due to other processes such as friction, we say that machine’s efficiency is high.
60
Q

How much effort (E) will be required to lift a rock if the rock (R) is 200 kg and the resistance arm (RA) is 1 meter and the effort arm (EA) is 4 meters long?

A
  • MA = R/E
  • Ea/Ra = R/E
  • E x Ea = R x Ra
  • E = (Ra x R) / Ea
  • E = (1m x 200kg) / 4m
  • E = 50kg
61
Q

What class of lever are scissors?

A
  • Class one.
62
Q

What class of lever is a wheelbarrow?

A
  • Class 2.
63
Q

What class of lever is a ratchet?

A
  • Class 2.
64
Q

What class of lever is driven axle and wheel of vehicle?

A
  • When the wheel is used to apply the effort, it acts as a class two lever. The axis of the wheel and axle act as the fulcrum, the radius of the wheel is the effort arm and the radius of the axles at resistance arm. For example, hand winches, wrenches, ratchets, and drive units are class two levers.
  • When the axle is used to apply the effort, it acts as a class 3 lever. The radius of the axle is now the effort arm and the radius of the wheel is the resistance arm. For example, the wheel and axle of a vehicle is a class 3 lever.
65
Q

What is the purpose of a single fixed pulley and load line?

A
  • The single, fixed pulley does not increase the applied force, but simply allows the force to change the direction. For example, pulling down moves to load up.
66
Q

What is the mechanical advance (MA) of a multiple pulley system if the number of rope parts around the lower pulley supporting the load is 6?

A
  • MA = 6
67
Q

What is the mechanical advantage in a belt drive when a 2-inch diameter drives a pulley with a 4-inch.?

A
  • MA = Driven diameter / Drive diameter
  • MA = 4 / 2
  • MA = 2
68
Q

What is the mechanical advantage in the chain drive when a sprocket with 10 teeth, drive a sprocket with 30 teeth?

A
  • MA = # of teeth on driven / #of of teeth on drive
  • MA = 30 / 10
  • MA = 3
69
Q

What is the RPM of the driven element in a Gear Drive when the driving gear has 10 teeth and an RPM of 800 and the driven gear 40 teeth?

A
  • RPM drive x #teeth drive = RPM driven x #teeth driven
  • Ratio
  • 4:1
  • RPM 200

Industrial Mechanic/Millwright (2 decks)

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