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Engineering Physics Flashcards

(85 cards)

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1
Q

Adiabatic Process

A

A thermodynamic process during which no heat enters or leaves a system

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2
Q

Brake Horsepower bhp

A

The output power from an engine expressed in imperial units where 1 horsepower = 746 watts

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3
Q

Calorific value

A

The measure of how much energy a fuel theoretically contains and releases when completely combusted. Also known as energy density. The typical units is Jkg^-1

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4
Q

Diesel engine

A

An internal combustion engine with a fairly high compression ratio, in which no fuel is introduced into the cylinder during compression.

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5
Q

Entropy

A

A measure of the degree of disorder of a system

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6
Q

First law of thermodynamics

A

The conservation of energy. In heat engines, the energy transferred to the system by heating is equal to the increase in internal energy and the work done by the system

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7
Q

Gyroscope

A

A device consisting of a wheel or disc that spins rapidly about an axis that is also free to change direction

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8
Q

Heat engine

A

A device that extracts energy from its environment in the form of heat and converts it into useful work.

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9
Q

Ideal gas

A

A gas that obeys Boyles law under all conditions: the gas has molecules that are infinitely small and exert no force on each other, except during collisions

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10
Q

Maximum theoretical efficiency

A

For a heat engine, the difference in temperature between the hot and cold reservoirs divided by the temperature of the hot reservoir. The maximum theoretical efficiency is always less than one.

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11
Q

Non flow processes

A

The four thermodynamic processes involving gases, isothermal, adiabatic, constant pressure and constant volume

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12
Q

Otto cycle

A

The indicator cycle (p-V) describing the petrol engine

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13
Q

Perpetual motion of the first kind

A

An imaginary machine which produces work without any energy input. This violates the first law of thermodynamics

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14
Q

Radians

A

One radian is equal to the angle subtended when the arc length is equal to the radius. (1 rad = 57.3’, 2(pi) rads = 360’)

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15
Q

Second law of thermodynamics

A

A law stating that heat naturally flows from a hot body to a cold body until both are at the same temperature.

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16
Q

Tangential acceleration

A

An increase in tangential velocity caused by an increase in angular velocity

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17
Q

Work done

A

In the context of thermodynamics, the energy given to a substance by a thermodynamic change.

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18
Q

Angular impulse

A

A change in angular momentum

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19
Q

Brake power

A

The output power from an engine

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20
Q

Carnot cycle

A

A theoretical thermodynamic cycle of two adiabatic and two isothermal changes, which is the most efficient possible

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21
Q

Dielectric constant

A

The dielectric constant or relative permittivity of a dielectric (Er), is the factor by which the electric field between two charges is decreased by the presence of the dielectric relative to a vacuum.

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22
Q

Energy storage capacity

A

The amount of total energy that can be stored mechanically through rotation of a flywheel, for example, to be released subsequently. It will depend on the angular velocity and the moment of inertia and is calculated by the kinetic energy equation 1/2xIx(w)^2

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23
Q

Flybrid

A

A mechanical system that converts a vehicles kinetic energy into rotational energy of a flywheel during braking, and reconverts energy back to the vehicle as kinetic energy when required

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24
Q

Heat pump

A

A device that transfers heat from a colder area to a hotter area by using mechanical energy, such as a refrigerator

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25
Ideal gas equation
An equation describing the relationship between the pressure, volume and absolute temperature of an ideal gas pV=nRT
26
Mechanical efficiency
The ratio of output (brake) power to indicated power for an engine
27
Output power
The driving power (also called brake power) that is delivered to the engines crankshaft
28
Perpetual motion machine of the second kind
An imaginary machine which turns heat energy totally into mechanical work. As no machine can convert heat totally into useful work, this violates the second law of thermodynamics
29
Refrigerator
A heat pump that takes in heat at low temperatures and rejects heat at higher temperatures
30
Sink
A heat reservoir
31
Tangential velocity
The instantaneous linear velocity of a rotating object. V=r(w)
32
Angular acceleration
The rate of change of angular velocity
33
Centripetal acceleration
The acceleration of an object moving at a steady speed in a circle directed towards the centre of the circle
34
Disordered
In the context of thermodynamics, the randomised kinetic energy of hot gas molecules
35
Flywheel
A rotating disc or wheel which stores kinetic energy as it spins
36
Hybrid car
A car with a combination of combustion engine and electric motor used to power it
37
Indicated power
The theoretical power that an engine can deliver
38
Inertia
The resistance of any object to a change in its state of motion
39
Working substance
The substance in a thermodynamic system that undergoes a change to its pressure, volume or temperature.
40
Torque
A turning effect, the moment of a couple about a point, units Nm
41
System
A thermodynamic system refers to a fixed mass of some substance, enclosed by a boundary
42
RPM
The rate at which an object turns is often given in terms of the number of full circles that are completed in a given time. This is the rotational frequency f, and is typically quoted in revolutions per minute
43
Principal specific heat capacities
The two principal heat capacities of a gas are: Cv, the energy required to produce unit temperature rise in unit mass of the gas at constant volume. And Cp, the energy required to produce unit temperature rise in unit mass of the gas at constant pressure
44
Overall efficiency
For an engine | Output power / input power
45
Moment of inertia
A measure of how the mass of a rotating body is distributed about its axis of rotation, driven by (sum)m(r^2) , units kg(m^2)
46
Isothermal process
A thermodynamic process that takes place under constant temperature conditions
47
Frictional torque
A frictional force which opposes (or causes) rotational motion
48
Cyclic process
In the context of thermodynamics, a process which continually repeats itself such as an engine running
49
Atomicity
The number of atoms in one molecule of a substance
50
Thermodynamics
The study of the movement of heat through systems
51
Surroundings
The region outside a thermodynamic system
52
Rotational kinetic energy
The kinetic energy of an object by virtue of its rotation, given by Ek = (1/2)I(omega^2)
53
Principle of conservation of angular momentum
The total angular momentum of a system remains constant provided there is no external torque
54
Internal energy
The sum of the total kinetic energy of the constituent particles of a system
55
Frictional power
The difference between the indicated power and output power of an engine
56
Cycle
A series of repeating pressure and volume changes describing a thermodynamic process
57
Angular velocity
The rate of change of angular displacement, rads^-1
58
Thermodynamic temperature scale
The Kelvin temperature scale
59
Steam engine
A heat engine in which the fuel combines with oxygen to generate steam which is then introduced into the engines cylinder
60
Revolution
A single complete cycle or turn about an axis of a rotating object, 2pi radians or 360'
61
Precession
The slow movement of the axis of a spinning body around another axis due to a torque
62
Internal combustion engine
A heat engine in which the fuel combines with oxygen inside the engines cylinder
63
Four stroke petrol engine
An internal combustion with a high compression ratio, in which fuel is introduced into the cylinder during compression
64
Compression ratio
The ratio of the volume enclosed in the cylinder of an engine at the beginning of the compression stroke to the volume enclosed at the end of the stroke
65
Angular momentum
A vector quantity in rotational motion, given by L=I(w)
66
Centripetal force
The force directed towards the centre of the circle, required to keep an object moving at a steady speed in a circle
67
Input power
The power that is derived from the burning of the fuel in a heat engine
68
Perpetual motion machine of the third kind
An imaginary machine with no frictional effects, so it can maintain its motion forever
69
Regenerative braking
A system to collect and store energy from a cars braking motion for reuse
70
Thermal efficiency
The ratio of the indicated power to the input power for an engine
71
Angular displacement
The angular displacement of a body is the angle in radians through which a point has been rotated about a specific axis
72
Coefficient of performance (COP)
In the context of refrigerators and heat pumps, the ratio of the heat extracted or supplied to the work done by the external agency
73
Indicator diagram
The pressure - volume diagram that describes the cycle of a heat engine
74
Power
The rate at which energy is transferred or at which work is done, measured in joules per second / watts
75
Reversible
In the context of thermodynamics, an infinitely slow change in the pressure, volume or temperature of a gas
76
Source
An energy or heat supply
77
What are two uses of flywheels
They can smooth out torque variations in vehicles. | They can recover and re use some of the kinetic energy that would otherwise be wasted through braking
78
Account for the difference between the indicated power and brake power
Power is expended: - overcoming friction in the bearings and between the piston and cylinder - circulating oil/cooling water - driving auxiliaries like the fuel pump
79
Explain why, in a Diesel engine, the fuel starts to be injected into the the cylinder slightly before the piston reaches its highest point in the cylinder
So that the fuel has partially started to burn when the piston is at the top of its stroke (so that maximum pressure is obtained when the piston is at top dead centre)
80
Explain what is meant by a reversed heat engine.
A device in which an input of work cause heat to transfer from a cold space to a hot space.
81
Explain why the COP of a reversed heat engine when operating as a heat pump is always greater the the COP when operating as a refrigerator
Heat transfer to a hot space equals work done plus heat transfer from cold space (Qin=W+Qout). So Qin is always greater than Qout. The COPhp=Qin/W and the COPref=Qout/w. So COPhp is always greater than COPref
82
Describe the problems associated with trying to design a real engine that uses an isothermal and adiabatic process
The isothermal process would require the engine to run very slowly and be made of a material of high heat conductivity. An adiabatic process has to occur very rapidly and would require a perfectly insulated container.
83
Describe and explain the way a washing machine drum accelerates at the start of its spin cycle
The acceleration will decrease up to the maximum constant angular velocity. This is because the clothes are moved to the outside of the drum, this increases the MoI and as T is constant, acceleration must decrease
84
State the law of conservation of angular momentum
The total angular momentum of a system remains the same provided no external torque acts on the system
85
What is the unit for angular momentum
Nms

Physics (3 decks)

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