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BMSc > BM unit 1 > Flashcards

BM unit 1 Flashcards

1
Q

how many base units are there

A

7

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2
Q

what are the 4 SI base units we need in the module

A

m
s
kg
k

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3
Q

what are derived units

A

formed by combining base units eg velocity, acceleration, force
eg N = kg m s-2

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4
Q

what is a supplementary unit we will use

A

rad

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5
Q

what are SI units

A

internationally agreed standard units of measurement

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6
Q

how do you convert from celsius to kelvin

A

add 273

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7
Q

what do positions and directions need to be given in relation to

A

reference frame

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8
Q

what is the most widely used 3D reference frame

A

rectangular co-ordinate system - cartesian co-ordinate system (x, y, z)

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9
Q

what is the origin

A

the point where all three axis cross

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10
Q

what is a plane

A

a flat surface, regarded as having zero thickness and are therefore 2 dimensional

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11
Q

what are the planes in the human body

A

coronal, sagittal, transverse

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12
Q

when are polar coordinates useful

A

when studying circular objects and when angles and rotations are important eg describing the motion of joints

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13
Q

difference between rectangular and polar coordinate systems

A

rectangular use displacements relative to perpendicular axes whereas polar use a displacement and rotations

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14
Q

what are the two forms that motion can take

A

linear and rotary
can do both at the same time eg football and walking (joints undergo a rotary motion while the combined rotations of the joints of the lower limb produce an overall linear movement)

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15
Q

what is displacement

A

the straight lined distance with a defined direction

it is a vector quantity (magnitude(distance) and direction)

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16
Q

what are scalars

A

a quantity that has magnitude only eg temperature

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17
Q

difference between speed and velocity

A 
speed = rate of change of distance travelled (scalar)
velocity = rate of change of displacement (vector)

velocity is therefore the same as speed but with added direction

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18
Q

equation for average velocity

A

av velocity = change in displacement/time

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19
Q

SI units of velocity

A

m s-1

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20
Q

define acceleration

A

rate of change of velocity

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21
Q

is acceleration scalar or vector

A

vector

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22
Q

SI units of acceleration

A

m s-2

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23
Q

equation for av acceleration

A

av acceleration = change in velocity/time taken

24
Q

when will acceleration be negative

A

during deceleration as the change in velocity is negative

25
Q

what effect will a force have on an object

A

deform the shape of the object and change the position of the object
note in rigid body mechanics the object cant be deformed

26
Q

how can we measure force

A

using a spring balance - spring inside a holder with a calibrated scale. hook at one end allows a force to be applied. string stretches in proportion to the applied force. strings balance scale shows the magnitude of the force acting parallel to the spring. scale is usually in N (SI unit of force)

27
Q

is force scalar or vector

A

vector

28
Q

what is static equilibrium

A

forces and moments acting on objects at rest or moving with constant velocity is statics. an object in static with no resultant force is in static equilibrium

29
Q

condition if static equilibrium

A

sum of all the external forces = 0

transitional equilibrium = static equilibrium along straight lines eg x, y, z

30
Q

what is newtons 3rd law

A

law of reaction

to every action there is an equal and opposite reaction

31
Q

define mass

A

the quantity of matter of which a body is composed

32
Q

define weight

A

the force of gravity acting on a body

33
Q

SI unit of mass

A

Kg

34
Q

SI unit of weight

A

N

35
Q

difference in weight and mass of astronauts on earth and moon

A

mass the same for both
on moon - weight much less as gravitational field is 1/6 of earths (on moon they are ‘weightless’ as the gravitational field is negligible)

36
Q

define density and equation

A

mass per unit volume. the density of a material always stays constant. If the mass of an object varies then the volume of the object will change proportionately.

density = mass/volume
p = m/V
37
Q

define gravity and what are its units

A

acceleration due to gravitational attraction. force of attraction increases as mass of bodies increase. it results in a body having weight
W=mg

g = 9.81 m s-2

38
Q

what is the centre of mass

A

a point where all the mass of an object can be assumed to act. the position will depend on how the mass is distributed in an object.

if rigid and symmetrical - COM will be at its geometric centre

each individual body segment can be considered to have its own COM

39
Q

where will COM in body be when standing upright

A

abdomen

40
Q

where will COM in body be when bending over

A

lies outside the body in front of the pelvis

41
Q

what is centre of gravity

A

a body in a gravitational field has a point where all the weight of the body is assumed to act
when a body has COM and COG they will act at the same point

42
Q

define pressure

equation and SI unit

A

force exerted per unit area
as magnitude of force increases, pressure increases, conversely as the size of the area increases the pressure decreases

pressure = force/area
P=F/A
SI unit = Pa

43
Q

what is the moment of a force

A

the tendency of a force to produce a rotation about an axis. it is also called torque
it is the product of the applied force and the moment arm (length of the line that passes through the centre of rotation and is perpendicular to the line of action of the force)
moment = force x moment arm (M=Fd)
units = N m

44
Q

rotational equilibrium

A

sum of all the external moments acting on the body must equal 0 - this is the 2nd condition of static equilibrium
if they are not the body will angularly accelerate

45
Q

what does a lever consist of

A

a rigid bar pivots around a fulcrum and is acted on by an effort force and a resistance force - both these forces produce moments about the fulcrum

46
Q

what is the effort arm in a lever

A

the length of the line that passes through the fulcrum and is perpendicular to the effort force

47
Q

what is the resistance force in a lever

A

the length of the line that passes through the fulcrum and is perpendicular to the resistance force

48
Q

use the human body to describe a lever system

A

muscles act - the effort force
to move or prevent the movement of a limb (the rigid bar)
by overcoming external forces (the resistance force) eg gravity

49
Q

two purposes of a lever system

A

amplify the effort force or to amplify the distance moved through

50
Q

what happens when the effort arm is longer than the resistance arm
give an example of this

A

the magnitude of the effort force required to overcome a given the resistance force is smaller than the magnitude of the resistance force. in this situation the lever is said to have mechanical advantage
an example of this is the crowbar rather than our fingers to move an object

51
Q

what happens when the resistance arm is longer than the effort arm

A

the resistance may be moved through a relatively large distance. in this case the lever system has mechanical disadvantage

in the human body muscles are usually at a force disadvantage, the forces produced by muscles are greater than the forces resisting them - this is because the muscles insertion point is closer to the fulcrum than the forces resisting them (usually insert close to a joint)

52
Q

equation for mechanical advantage and explain what the results would mean

A

MA = effort arm/resistance arm
MA >1 - lever system is working at a mechanical advantage and the effort force is less than the resistance force
MA <1 - mechanical disadvantage

53
Q

how many classes of lever systems are there

A

3

54
Q

describe a first class lever system and give examples

A

fulcrum between the effort and resistance
eg crowbar, scissors, see-saw
it can work at either a mechanical advantage or disadvantage

55
Q

describe a second class lever system and give examples

A

resistance force between fulcrum and effort
eg wheelbarrow, nutcracker
always works at a mechanical advantage

56
Q

describe a third class lever system and give examples

A

effort located between fulcrum and resistance
eg fishing rod, tweezers, many human joints
always works at a mechanical disadvantage

BMSc (10 decks)

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