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BMSc SB > Mechanics Unit 1 > Flashcards

Mechanics Unit 1 Flashcards

1
Q

there are 7 SI base units - which 3 do we need to know

A

metre (m) - measure of length
second (s) - measure of time
kilogram (kg) - measure of mass

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2
Q

there are 2 supplementary SI units - which 1 do we need to know

A

radian (rad) - measure of angle

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3
Q

what is 2 pie radians equal to

A

360 degrees

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4
Q

how can we convert radians into degrees

A

180/pie multiply by angle in radians

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5
Q

how can we convert degrees into radians

A

pie/180 multiply by angle in degrees

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6
Q

what is the definition of a scalar and vector quantity

A

scalar = quantity with magnitude only

vector = quantity with magnitude and direction

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7
Q

list some vector quantities

A 
displacement 
velocity 
angular displacement 
angular velocity 
force
momentum 
acceleration
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8
Q

what are the 2 ways to write location of a vector

A

Cartesian system - x, y and z axis

Polar co-ordinates - resultant vector and angle in degrees

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9
Q

equation for average velocity

A

change in displacement / time taken

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10
Q

on a displacement-time graph, how can the velocity be calculated

A

the gradient of the graph is the velocity

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11
Q

what is instantaneous velocity on a displacement-time graph

A

the gradient on the graph at a certain point

- can be found drawing a tangent to the curve to find slope and calculate a gradient

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12
Q

equation for acceleration

A

change in velocity / time taken

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13
Q

unit for velocity

A

m/s

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14
Q

unit for acceleration

A

m/s^2

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15
Q

what needs to be considered when calculating acceleration

A

acceleration due to gravity = 9.81m/s^2

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16
Q

what graph can be used to calculate acceleration

A

velocity-time graph

- the gradient is the acceleration

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17
Q

what do the letters u, v, a, s and t stand for

A

u = starting velocity (m/s)

v = final velocity (m/s)

a = acceleration (m/s^2)

s = displacement (m)

t = time taken (s)

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18
Q

what are the equations of linear motion

A

v = u + at

v^2 = u^2 + 2as

s= 1/2 (u + v)t

s = ut + 1/2at^2

s = vt - 1/2at^2

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19
Q

what is rotary motion

A

object rotating about a point on itself or about an external fixed point

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20
Q

what is angular velocity

A

angular displacement travelled per second

i.e. change in angular displacement / time taken

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21
Q

what is the unit for angular velocity

A

rad/s

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22
Q

what is instantaneous angular velocity

A

angular velocity at an instant time

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23
Q

what is angular acceleration and its units

A

rate of change of angular velocity

rad / s^2

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24
Q

equation of angular acceleration

A

change in angular velocity / time taken

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25
unit of Force
Newton (N)
26
what is 1N equal to
1 kg m/s^2
27
what is the 2 effects of a force
change the body's position deform the body's shape
28
what is rigid body mechanics
when it is assumed that the bodies are rigid under the force i.e. they do not deform
29
what is one way to measure force
calibrated spring balance
30
what is mass, its unit and how it is denoted in formulas
quantity of matter of which a body is composed Kg m
31
what is weight, its unit and how it is denoted in formulas
force of gravity acting on a body Newton W
32
convert mass into weight
weight = mass x gravity gravity = 9.81 m/s^2
33
convert weight into mass
mass = weight/gravity
34
what is density
mass per unit volume
35
equation and unit of density
density = mass/volume unit = kg/m^3
36
what is important to remember about the density of a material
density of a material remains constant if the mass of a body varies then the volume of the body will change proportionately
37
what is the definition of gravity
acceleration due to gravitational attraction between two bodies
38
how is gravity denoted in formulas and what is its unit
g m/s^2
39
what is centre of mass and what does its location depend on
point where all the mass of the body can be assumed to act location depends on distribution of mass in the object
40
what is the centre of gravity
point where the weight of the body can be assumed to act | astronauts would not have a centre of gravity
41
true or false - centre of mass always lies within the body
false - when leaning forward, centre of mass shifts to outside the pelvis
42
what is the definition of friction and what is its unit
force arising between two surfaces when they rub together Newton
43
what does the amount of friction depend on
roughness of the surfaces and magnitude of force pushing them together
44
what is the measurement of the maximum friction force between 2 surfaces
co-efficient of friction
45
what is the equation of co-efficient of friction
co-efficient of friction = Friction force / forces acting normally to the surface
46
what are the 3 types of friction
static, sliding and rolling
47
when does static friction only exist
when motion is ABOUT to occur between 2 surfaces - static friction force present is just sufficient to oppose the applied force
48
when does sliding friction only exist
when sliding occurs between two surfaces
49
what is the relationship between static and sliding friction
sliding friction is LESS than static friction more force is required to start a body moving against a frictional force than to keep it moving
50
what is the equation for calculating maximum force
Fmax = Weight x friction co-effecient
51
what is unit for maximum force
Newton
52
what is definition of pressure
force exerted per unit area on a surface [i.e. as size of area increases, pressure decreases]
53
equation and unit for pressure
pressure = force / area unit = Pascal (Pa) [area should be in metres squared]
54
what is static equilibrium in force analysis
no resultant force, all the forces are perfectly balanced no change in state of motion NO ACCELERATION i.e. can be in constant linear/angular velocity
55
what is Newton's III Law
To every action there is an equal and opposite reaction
56
what is the equation for Force
Force = mass x acceleration
57
what is Newton's I law and what is it called
Every body remains at rest or moving at constant velocity unless it is acted upon by a resultant force Law of inertia
58
what is inertia and what is it represented by in the body
a body has a certain reluctance to accelerate which is its inertia a body's inertia is represented by its mass
59
what what is Newton's II law and what is it called
The acceleration of a body is proportional to the applied force and inversely proportional to its mass Law of acceleration
60
what is equation for acceleration
acceleration = force / mass [rearranged from force = mass x acceleration]
61
what is forward dynamics
finding the acceleration due to known forces acting on the body
62
what is backwards dynamics
working out forces when motion is known
63
what is dynamic equilibrium
when sum of forces does not equal zero [left with resultant unbalanced force]
64
what is the equation for inclined plane
mgsin(theta) where m = mass, g = gravity
65
what is the equation for perpendicular plane
mgcos(theta)
66
what is momentum
body's resistance to change its motion and its velocity
67
equation for momentum and units
momentum = mass x velocity unit = kg m/s or N s (newton second)
68
how does Newton's II law applied to momentum
the rate of change of linear momentum is proportional to the applied force
69
what does Conservation of momentum mean
total momentum before collision is equal to total momentum after collision.
70
what is the equation for rate of change of motion
Force = mass(final velocity - initial velocity) / time
71
what is Newton's I law in relation to momentum
a body will continue to move with constant momentum unless an external force acts to change that momentum
72
what is a moment of a force
is the tendency of a force to produce a rotation about an axis
73
what is the equation and units of a moment
moment = force x radius units = Newton metres (Nm)
74
what is rotational equilibrium
when the sum of all moments equals zero
75
what are the 3 components of a lever system
rigid bar fulcrum effort and resistance force
76
in the human body, what parts are the rigid bar, effort force and the resistance force
rigid bar - limb effort force - muscles contracting resistance force - external force e.g. gravity
77
what is the equation to calculate mechanical advantage
effort distance / resistance distance MA = df / dr
78
in the human body lever system, what are muscles normally at
mechanical disadvantage | i..e forces produced by the muscles are greater than the forces resisting them
79
why are muscles at mechanical disadvantage
the muscles insertion point tend to be closer to the fulcrum than the resistance force i.e. have a smaller effort arm also speed of movement i.e. closer muscle is attached, smaller the contraction needed to make a larger movement and the quicker the movement
80
what is a first class lever system and an example of it
when the fulcrum is located between the effort and the resistance e.g. crowbar system can be in either mechanical advantage or disadvantage depending on the length of the effort arm
81
what is a second class lever system and an example of it
when the resistance is located between the effort and the fulcrum e.g. wheelbarrow system is at mechanical advantage as effort arm is always longer than resistance arm.
82
what is a third class lever system and an example of it
when the effort is located between the fulcrum and the resistance e.g. fishing rods, human body lever system system is at mechanical disadvantage as effort arm is always shorter than resistance arm.
83
what is the equation for the tangential linear velocity
tangenital linear velocity = radius x angular velocity
84
what is the equation for tangential acceleration and what does it represent
tangential acceleration = radius x angular acceleration represents the linear acceleration directed at a tangent to the circle formed by the motion.
85
when summing the moments around the fulcrum, which way is positive and which way is negative
``` anti-clockwise = positive clockwise = negative ```
86
when is tangential acceleration = 0
uniform angular motion (i.e. when the body rotates with a constant angular velocity).
87
equation for radial acceleration, the second equation for radial acceleration and what is it also called
radial acceleration = radius x angular velocity^2 OR radial acceleration = velocity^2 / radius centripetal acceleration i.e. towards the centre
88
what is moment of inertia and what is it dependant on
a quantity expressing a body's tendency to resist angular acceleration body's mass and how the mass is distributed
89
how do you calculate the moment of a rotating object
M = I x alpha where I = moment of inertia alpha = angular acceleration
90
what is the equation to calculate moment of inertia and what is the unit
I = m x r^2 r = radius of gyration [can also be noted as k] unit = kg m^2
91
what is a way to roughly guess who has the biggest moment of inertia
the bigger the radius, the bigger the moment of inertia
92
what is angular momentum and what principle also applies to angular momentum
incorporates a body's resistance to change its rotatory motion (inertia) and its angular velocity the principle of conservation of momentum
93
what is equation for angular momentum, and the units
angular momentum = moment of inertia x angular velocity ``` L = I x omega Unit = kg m^2 rad s^-1 ```
94
what are the 2 assumptions of bio-mechnical models
1. the body segments are rigid. | 2. the joints are frictionless.
95
given that it is assumed that body segments are rigid, what else is assumed
1. the position of the centre of mass remains fixed relative to the segment. 2. the moment of inertia of each segment remains constant. 3. the length of each segment remains constant.
96
what is Anthropometry and what parameters are needed to calculate it
to calculate the human body's size and form length, mass, centre of mass and radius of gyration
97
why would the radius of gyration be larger at the proximal end than the distal end
because more mass is distributed further from the proximal end than the distal end
98
equation to calculate work done and units
work done = force x distance w = Fs unit = Joules
99
what is the equivalent unit of Joules
1 kg m^2 s^-2
100
what is 'work'
occurs when a force moves a body
101
what is 'power'
rate at which energy is expended or work is done
102
equation of power and unit
power = work done / time taken p = w/t unit = watt (W)
103
what is the equivalent of 1 watt
1 J s^-1
104
what is energy and its unit
the capacity to do work unit = Joules (J)
105
what is the equation for linear kinetic energy
KE = 1/2 x mass x velocity^2 KE = 1/2mv^2
106
what is the equation for rotary kinetic energy
KE = 1/2 x moment of inertia x angular velocity ^2
107
what is the definition of kinetic energy and potential energy
KE = energy possessed by a body due to its motion PE = energy possessed by a body because of its position
108
what is the equation for PE
``` PE = mass x gravity x height OR = weight x height ```
109
what is the 1st law of thermodynamics
Conservation of Energy - energy cannot be created or destroyed - energy can be changed from one form to another.
110
what does conservation of energy mean in terms of KE and PE
PE = KE
111
if 2 objects were dropped from the same height, one at 10kg mass and one at 20kg mass, which would hit the ground first?
would hit the ground simultaneously PE = KE therefore mgh = 1/2 mv^2 rearrange v = square root of 2 x gravity x height therefore, velocity is independent of mass
112
what is the relationship between acceleration due to gravity and mass
acceleration due to gravity is independent of mass
113
what are the aerodynamic forces
``` relative velocity type of flow - laminar or turbulent drag lift magnus effect ```
114
what is laminar flow
when air flows in a smooth regular manner
115
what is turbulent flow
when the regular smooth flow breaks down and the path that air particles take are random and unordered
116
what can be used to predict whether an object will have laminar or turbulent flow
Reynolds Number RE = {air density x diameter x velocity} divided by air viscosity RE < 2000 = flow will be laminar RE > 3000 = flow will be turbulent
117
why are golf balls dimpled
to cause less drag
118
what is the magnus effect
occurs when projectiles spin - one side of the ball, A, will have a higher flow velocity than the other side of the ball, B. - means pressure on side A is less than that of side B think of the banana shot in football free kicks.
119
multiplication factors
``` kilo = k = 10 ^ 3 mega = M = 10 ^ 6 G = 10 ^ 9 ``` ``` centi = c = 10 ^ -2 milli = m = 10 ^ -3 micro = 10 ^ -6 ```

BMSc SB (18 decks)

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