Mechanics: Unit 1 Motion (class + online) Flashcards
What is mechanics?
a branch of physics that analyses the action of forces on matter or material bodies
What is force?
something that displaces and/or deforms a body
What can statics be used for?
to calculate unknown forces
Which of kinetics and kinematics considers force?
kinetics
What is kinematics?
it quantifies motion by how it moves in 3d space
What is kinetics?
looks at the relationship between force and motion
What are the two areas of mechanics?
rigid and deformable body
In classical mechanics, what do the terms
a) reductionistic
b) deterministic
mean?
a) reducing a complex problem into simpler parts
b) if we have a set of initial conditions we can work forward/bckward and distinguish a solution
What is a translational movement?
a linear movement ie. in a straight line
What is the difference between rectilinear and curvilinear?
rectilinear is an actual straight line whereas curvilinear isnt perfectly straight but there is no rotation
What do rotary movements in walking allow for?
linear movement of the whole body
What system is used for measurement?
SI aka metric
How do we measure
a) length
b) time
c) mass
a) metre
b) second
c) kilogram
how many metres in
a) km
b) cm
c) mm
d) micrometre
a) 1000
b) 0.01
c) 0.001
d) 0.000001
what is angular distance and which SI unit does it use?
the total angle turned through
rads
what is a rad ? and what is it equal to?
2 π rads = 360
about 57 degrees
one radian encloses an arc which has a length equal to the circle radius
what is a newton?
kilogram metres per second squared
kg m s-2
what are the four basic physical quantities?
time
angle
temperature
distance
What symbol represents
a) angle in degrees?
b) angle in rads?
a) phi Φ
b) theta θ
How do we convert radians to degrees ?
degrees = (radians x180/ π)
How do we convert degrees to radians?
radians = (degrees xπ /180)
What does zero degrees kelvin represent?
the point at which matter has no energy
How can you convert celsius to kelvin?
add 273
What are positions and directions given in reference to?
a reference frame
What are the two co-ordinate systems that positions in reference frames are related to?
the rectangular co-ordinate system or the polar co-ordinate system.
What is another name for the rectangular reference frame?
cartesian
What is a vector?
a quantity with magnitude (length) and direction
What is a scalar?
a quantity with only magnitude
Name some vectors
displacement (inc angular) velocity (inc angular) force momentum acceleration
Name some scalars
distance speed angle rotation rate mass temperature energy
What is the difference between distance and displacement?
distance is a scalar because it is just a measure of how far but displacement is a vector because it also takes direction into account
What is angular displacement?
when something is rotated through an angle in a clockwise or anticlockwise direction
has both a magnitude and a direction
How do you add or subtract two or more vectors?
via graphs or trigonometry to give a resultant vector
When resolving a vector, if the resultant vector faces
a) north west (ie. positive vertical but negative horizontal)
b) south west (ie. negative vertical and horizontal)
how do we calculate the angle?
a) +180
b) -180
What do you call axes which are all at right angles to each other?
orthogonal
in which type of system does a change in one axis not affect the others?
orthogonal
describe a plane
a 2d structure with no thickness encompassing 2 axes of a 3D co-ordinate system
what happens when 2 planes cross each other?
a straight line is formed
how many planes can be at right angles to each other?
max is 3
how is position expressed in the polar coordinates system for 2D structures?
(rc, θc)
where rc = length of line
θc = angle of line
When are polar co-ordinates more useful than rectangular co-ordinates?
in the studies of circular objects and where angles and rotations are important
What is the origin?
the point where all axes cross (0,0,0)
What is the difference between speed and velocity?
speed is a scalar, the rate of change of distance travelled
velocity is a vector, the rate of change of displacement (so direction is included)
What are the SI units of velocity?
metres per second (m s-1)
how do you work out the average velocity?
change in displacement over time
What is acceleration?
the rate of change of velocity
Is acceleration a scalar or a vector quantity?
a vector quantity
What are the SI units of acceleration?
m s-2
What is the SI unit of force?
the newton (N)
how is position expressed in the polar coordinates system for 3D structures?
(rc, θc, Φc )
What do we call the movement of an object in a straight line with no rotation taking place?
translation
What do we call the movement of an object in a circular path with no translation taking place?
a rotation
How many degrees of freedom does unconstrained movement have?
6 degrees of freedom
- 3 translational (x,y,z)
- 3 rotational
how many degrees of freedom does a snooker ball have rolling on a table?
5 degrees of freedom
- 2 translational
- 3 rotational
how many degrees of freedom does a door handle have?
1 rotational
compare the degrees of freedom of a ball and socket joint to a hinge joint?
ball and socket eg hip has 3 rotational
hinge joint eg knee has 1 rotational
How do we display velocity data?
displacement-time graphs
with velocity being equal to the gradient
What is instantaneous velocity and how do we work it out?
it is the velocity at an instant in time
it is equal to the gradient on the displacement-time graph at a certain point
work it out by drawing a tangent
How do we work out average acceleration?
change in velocity over time
= ms-2
What is the acceleration of something falling due to gravity?
9.81m/s2
How do we display acceleration data?
velocity-time graph
What is the gradient of the velocity-time graph equal to?
acceleration
What is the area under the velocity-time curve equal to?
total displacement ie the velocity
What are the four parameters used to describe rotary motion?
time
angular displacement
angular velocity
angular acceleration
What does the symbol a represent?
alpha is used to represent angular acceleration (rad/s2)
what does the symbol ω represent?
omega is used to represent angular velocity (rad/s)
what is angular velocity?
the angular displacement travelled per second
how can we find the angular velocity?
plotting an angle-time graph
what is angular acceleration?
the rate of change of angular velocity
what is the gradient of an angular velocity-time graph equal to?
angular acceleration
what do a) u b) v c) a d) s e) t represent in the equations of linear motion?
a) starting velocity
b) final velocity
c) acceleration
d) displacement
e) time taken
How can we calculate final velocity?
v = u + at
final velocity = starting velocity + (acceleration x time)
Give 3 linear equations including displacement
v2 = u2 + 2as
s = 1/2 ( u + v) t
s= ut + 1/2 a t2
What is the multiplication factor for the prefix giga?
10 to the 9
What is the multiplication factor for the prefix mega ?
10 the 6
What is the multiplication factor for the prefix kilo?
10 to the 3
What is the multiplication factor for the prefix centi?
10 to the -2
What is the multiplication factor for the prefix milli?
10 to the -3
What is the multiplication factor for the prefix micro?
10 to the -6
What is the multiplication factor for the prefix nano?
10 to the -9
What is the symbol for angular displacement?
θ
How can we measure force?
calibrated spring balance
