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Engineering Physics Flashcards

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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
Q

Ideal gas equation

A

An equation describing the relationship between the pressure, volume and absolute temperature of an ideal gas pV=nRT

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26
Q

Mechanical efficiency

A

The ratio of output (brake) power to indicated power for an engine

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27
Q

Output power

A

The driving power (also called brake power) that is delivered to the engines crankshaft

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28
Q

Perpetual motion machine of the second kind

A

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

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29
Q

Refrigerator

A

A heat pump that takes in heat at low temperatures and rejects heat at higher temperatures

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30
Q

Sink

A

A heat reservoir

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31
Q

Tangential velocity

A

The instantaneous linear velocity of a rotating object. V=r(w)

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32
Q

Angular acceleration

A

The rate of change of angular velocity

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33
Q

Centripetal acceleration

A

The acceleration of an object moving at a steady speed in a circle directed towards the centre of the circle

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34
Q

Disordered

A

In the context of thermodynamics, the randomised kinetic energy of hot gas molecules

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35
Q

Flywheel

A

A rotating disc or wheel which stores kinetic energy as it spins

36
Q

Hybrid car

A

A car with a combination of combustion engine and electric motor used to power it

37
Q

Indicated power

A

The theoretical power that an engine can deliver

38
Q

Inertia

A

The resistance of any object to a change in its state of motion

39
Q

Working substance

A

The substance in a thermodynamic system that undergoes a change to its pressure, volume or temperature.

40
Q

Torque

A

A turning effect, the moment of a couple about a point, units Nm

41
Q

System

A

A thermodynamic system refers to a fixed mass of some substance, enclosed by a boundary

42
Q

RPM

A

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
Q

Principal specific heat capacities

A

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
Q

Overall efficiency

A

For an engine

Output power / input power

45
Q

Moment of inertia

A

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
Q

Isothermal process

A

A thermodynamic process that takes place under constant temperature conditions

47
Q

Frictional torque

A

A frictional force which opposes (or causes) rotational motion

48
Q

Cyclic process

A

In the context of thermodynamics, a process which continually repeats itself such as an engine running

49
Q

Atomicity

A

The number of atoms in one molecule of a substance

50
Q

Thermodynamics

A

The study of the movement of heat through systems

51
Q

Surroundings

A

The region outside a thermodynamic system

52
Q

Rotational kinetic energy

A

The kinetic energy of an object by virtue of its rotation, given by Ek = (1/2)I(omega^2)

53
Q

Principle of conservation of angular momentum

A

The total angular momentum of a system remains constant provided there is no external torque

54
Q

Internal energy

A

The sum of the total kinetic energy of the constituent particles of a system

55
Q

Frictional power

A

The difference between the indicated power and output power of an engine

56
Q

Cycle

A

A series of repeating pressure and volume changes describing a thermodynamic process

57
Q

Angular velocity

A

The rate of change of angular displacement, rads^-1

58
Q

Thermodynamic temperature scale

A

The Kelvin temperature scale

59
Q

Steam engine

A

A heat engine in which the fuel combines with oxygen to generate steam which is then introduced into the engines cylinder

60
Q

Revolution

A

A single complete cycle or turn about an axis of a rotating object, 2pi radians or 360’

61
Q

Precession

A

The slow movement of the axis of a spinning body around another axis due to a torque

62
Q

Internal combustion engine

A

A heat engine in which the fuel combines with oxygen inside the engines cylinder

63
Q

Four stroke petrol engine

A

An internal combustion with a high compression ratio, in which fuel is introduced into the cylinder during compression

64
Q

Compression ratio

A

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
Q

Angular momentum

A

A vector quantity in rotational motion, given by L=I(w)

66
Q

Centripetal force

A

The force directed towards the centre of the circle, required to keep an object moving at a steady speed in a circle

67
Q

Input power

A

The power that is derived from the burning of the fuel in a heat engine

68
Q

Perpetual motion machine of the third kind

A

An imaginary machine with no frictional effects, so it can maintain its motion forever

69
Q

Regenerative braking

A

A system to collect and store energy from a cars braking motion for reuse

70
Q

Thermal efficiency

A

The ratio of the indicated power to the input power for an engine

71
Q

Angular displacement

A

The angular displacement of a body is the angle in radians through which a point has been rotated about a specific axis

72
Q

Coefficient of performance (COP)

A

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
Q

Indicator diagram

A

The pressure - volume diagram that describes the cycle of a heat engine

74
Q

Power

A

The rate at which energy is transferred or at which work is done, measured in joules per second / watts

75
Q

Reversible

A

In the context of thermodynamics, an infinitely slow change in the pressure, volume or temperature of a gas

76
Q

Source

A

An energy or heat supply

77
Q

What are two uses of flywheels

A

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
Q

Account for the difference between the indicated power and brake power

A

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
Q

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

A

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
Q

Explain what is meant by a reversed heat engine.

A

A device in which an input of work cause heat to transfer from a cold space to a hot space.

81
Q

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

A

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
Q

Describe the problems associated with trying to design a real engine that uses an isothermal and adiabatic process

A

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
Q

Describe and explain the way a washing machine drum accelerates at the start of its spin cycle

A

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
Q

State the law of conservation of angular momentum

A

The total angular momentum of a system remains the same provided no external torque acts on the system

85
Q

What is the unit for angular momentum

A

Nms

Physics (3 decks)

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