Mechanics & Materials Flashcards

1
Q

Acceleration

A

Change of velocity per unit time.

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2
Q

Acceleration of free fall

A

Acceleration of an object acted on only by the force of gravity.

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3
Q

Braking distance

A

The distance travelled by a vehicle in the time taken to stop it.

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4
Q

Breaking stress

A

Tensile stress needed to break a solid material.

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5
Q

Brittle

A

Snaps without stretching or bending when subject to stress.

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6
Q

Centre of mass

A

The centre of mass of the body is the point through which a single force on the body has no turning affect.

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7
Q

Conservation of momentum

A

For a system of interacting objects is the total momentum of the objects Remains constant provided no external resultant force acts on the system.

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8
Q

couple

A

pair of equal and opposite forces acting on a body but not along the same line.

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9
Q

density of a substance

A

mass per unit volume of the substance.

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10
Q

displacement

A

distance in a given direction.

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11
Q

dissipative forces

A

forces that transfer energy which is wasted.

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12
Q

drag force

A

the force of fluid resistance on an object moving through the fluid.

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13
Q

ductile

A

stretches easily without breaking.

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14
Q

efficiency

A

the ratio of useful energy transferred (or the useful work done) by a machine or device to the energy supplied to it.

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15
Q

Effort

A

the force applied to a machine to make it move

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16
Q

elastic collision

A

an elastic collision is one in which the total kinetic energy after the collision is equal to the total kinetic energy before the collision

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17
Q

elastic limit

A

point beyond which a wire is permanently stretched

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18
Q

elasticity

A

property of a solid that enables it to regain its shape after it has been deformed or distorted

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19
Q

energy

A

the capacity to do work

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20
Q

equilibrium

A

state of an object when at rest or in uniform motion

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21
Q

explosion

A

when two objects fly apart and the two objects carry away at opposite and equal momentums

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22
Q

force

A

rate of change of momentum(mass x acceleration for fixed mass).

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23
Q

free-body force diagram

A

a diagram of an object showing only the forces acting on the object.

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24
Q

friction

A

force opposing the motion of a surface that moves or tries to move across another surface.

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25
Q

fusion (thermal)

A

the fusing together of metals by melting them together.

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26
Q

gravitational force

A

an attractive force that acts equally on any two objects due to their mass.

27
Q

Hooke’s law

A

the extension of a spring is proportional to the force needed to extend it up to a limit referred to as its limit of proportionality.

28
Q

impulse

A

of a force acting on an object, force x time for which the force acts.

29
Q

inertia

A

resistance of an object to change its motion.

30
Q

Kinetic energy

A

The energy of a moving object due to its motion E=1/2mv^2

31
Q

load

A

the force to be overcome by a machine when it shifts or raises an object

32
Q

mass

A

measure of the inertia or resistance to a change of motion of an object

33
Q

moment of a force about a point

A

force x perpendicular distance from the line of action of the force to the point (pivot)

34
Q

momentum

A

mass x velocity, its unit is kgm/s

35
Q

motive force

A

the force that drives a vehicle

36
Q

Newton’s First Law of Motion

A

An object continues at rest or in uniform motion unless it is acted on by a resultant force

37
Q

Newton’s Second Law of Motion

A

The rate of change of momentum of an object is proportional to the resultant force on it (resultant force = change in momentum/change in time)

38
Q

Newton’s Third Law of Motion

A

When two objects interact, they exert equal and opposite forces on one another

39
Q

Pascal

A

Unit of pressure or stress equal to 1 Nm^-2

40
Q

Plastic Deformation

A

Deformation of a solid beyond its plastic limit

41
Q

Potential Energy

A

The energy of an object due to its position

42
Q

Power

A

Rate of transfer of energy= energy transferred/time taken

43
Q

Pressure

A

The force per unit area that a gas or a liquid or a solid at rest exerts normally on (i.e. at right angles to) a surface. Pressure is measured in pascals (Pa), where 1 Pa=1 Nm-2

44
Q

Principle of conservation of energy

A

in any change, the total amount of energy after the change is always equal to the total amount of energy before the change

45
Q

Principle of conservation of momentum

A

when two or more bodies interact, the total momentum is unchanged, providing no external forces act on the bodies.

46
Q

Principle of moments

A

for an object in equilibrium, the sum of the clockwise moments about any point= the sum of the anticlockwise moments about that point

47
Q

Projectile

A

a projected object in motion acted on only by the force of gravity

48
Q

scalar

A

physical quantity with magnitude only

49
Q

speed

A

change in distance per unit time

50
Q

stiffness constant

A

force per unit extension needed to extend a spring or wire

51
Q

stopping distance

A

sum of the thinking and braking distances

52
Q

strain

A

extension per unit length of a solid when deformed

53
Q

stress

A

force per unit cross-sectional, perpendicular area in a solid

54
Q

terminal speed

A

maximum speed reached by an object when the drag force on it is equal and opposite to the force causing the motion of the object

55
Q

thinking distance

A

distance travelled by a vehicle in the time it takes the driver to react

56
Q

Ultimate tensile stress

A

Tensile stress needed to break a solid material.

57
Q

Useful energy

A

Energy transferred to where it is wanted when it is wanted.

58
Q

Vector

A

A physical quantity with magnitude and direction.

59
Q

Velocity

A

Change of displacement per unit time.

60
Q

Weight

A

The force of gravity acting on an object.

61
Q

Work done

A

Work is energy transferred by means of a force. Work = force x distance moved in the direction of the force. The work done W by a force F when its point of application moves through displacement s at angle (theta) to the direction of the force is given by W = Fs cos (theta).

62
Q

yield point

A

point at which the stress in a wire suddenly drops when the wire is subjected to increasing strain

63
Q

Young modulus

A

tensile stress/strain (assuming the limit of proportionality has not been exceeded). The unit of the Young modulus is the pascal (Pa) which is equal to 1 N/m2