# Chapter3x

Μηχανική

14 Νοε 2013 (πριν από 2 χρόνια και 11 μήνες)

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Kinematics

Kinematics

is the branch of physics that
describes the motion of points, bodies
(objects) and systems of bodies (groups of
objects) without consideration of the causes
of motion.

Kinematics

One
-
dimensional kinematics. Movement
along one axis.

Distance

the total distance traveled from
beginning to end. It always has a positive
value
. A scalar quantity

completely
characterized only by magnitude.

Displacement

the change in position
. A
vector quantity completely characterized by
magnitude and direction.

Kinematics

Average speed

distance
divided
by elapsed
time
.

Average velocity

displacement divided by
elapsed time
.

Some units for speed and velocity are
and any unit of length divided by a unit of
time.

,,
m km mi
s h h
Kinematics

Instantaneous speed

the speed at a given
instant.

Instantaneous
velocity

the velocity at a given
instant.

Kinematics

Average acceleration

the change in velocity
divided but
the
change in time.

f i
av
f i
v v
v
a
t t t

 
 
Kinematics

Instantaneous acceleration

the acceleration
at a given instant.

Kinematics

Constant acceleration

when acceleration is
constant, instantaneous acceleration is equal
to the average acceleration.

In this course
we will
only be dealing with
situations involving constant acceleration.

Kinematics

In the following slide the subscript
i

refers to
an initial
condition
, and the subscript
f

refers
to
a final condition.

Table 2
-
4

Constant
-
Acceleration Equations of Motion

Variables Related

Equation

Velocity, time,
acceleration

v
f

=
v
i

+
at

Initial, final, and
average velocity

v
av

= ½(
v
f

+
v
i

)

Position, time,
velocity

d

= ½(
v
f

+
v
i
)
t

Position, time,
acceleration

d

=
v
i
t

at
2

Velocity, position,
acceleration

v
f
2

=
v
i
2

+ 2
a
d