Time passes.
Will you?
1st atomic clock
when something occurs (an event)
I. Time t is___________________________________
It is a _____________________________
scalar (no direction)
events
In physics, the time between two ___________
is
time interval
is called the ___________________________
.
event 1
occurs at t = ti
event 2
occurs at t = tf
For example, if…
initial
ti = ____________
time =
5.0 s
final
tf = ____________
time =
8.5 s
Then the time interval: tf – ti = Dt equals
Dt = tf – ti =
8.5 s -
5.0 s =
3.5 s
positive
The time interval will always be ______________
.
Dt
In Regents Physics, instead of ________
, we use
the symbol _____
for time intervals and often just
t
call it the ____________
. Remember that _____
time
t
how long a certain process lasts
represents ____________________________________
.
second, s
The basic unit for time is the __________________
.
minutes, hours, etc
Other units, such as ___________________________
seconds
must usually be converted into _________________
before solving any problems.
How fast is Usain Bolt?
What is the fastest speed possible?
how fast an object moves
II. speed v = _______________________________
time rate of change in distance
=________________________________
a scalar (no dir., only mag.)
=_________________________________
Ex:
v = 55 mph
mag.
constant
Speed v can be ______________
(not changing), or
it can change. If it changes, the speed at any
instantaneous
instant is called the ____________________
speed.
average
The ______________speed,
vavg = v is:
Equation for v from PRT
(Physics Reference Tables):
Physics Reference Tables, last page:
Further down, find:
how fast an object moves
speed v = ______________________
time rate of change in distance
=____________________________________
a scalar (no dir., only mag.)
=_____________________________________
Ex: v = 55 mph
mag.
constant
Speed v can be ______________
(not changing), or
it can change. If it changes, the speed at any
instantaneous
instant is called the ____________________
speed.
average
The ______________speed,
vavg = v is:
Equation for v from PRT
(Physics Reference Tables):
v
= d/t
Ex: Jenny runs 95 meters in 15 seconds.
Find her average speed. Show all work.
v
= d/t
= 95 m/15 s
= 6.3 m/s
derived
____________
units are made
up of…..
fundamental
…the 4 _____________________
(basic) units:
m, A, s, kg
meter, Ampere, second, kilogram
Ex. A car, initially moving at a speed of 25 m/s,
increases its speed to 45 m/s in 3.0 seconds.
What is its average speed during the 3.0 s?
initial
vi = ____________
speed =
25 m/s
final
vf = ____________
speed =
45 m/s
v = (vi + vf)
2
 This equation is NOT
in your PRT. You must
memorize it
_____________________
.
v = (25 m/s + 45 m/s)
2
= 35 m/s
How far will the car in the last example
travel in 12 seconds?
Given:
v
t = 12 s
v = 35 m/s
35 m/s = d/12 s
420 m
Unknown: d =
= d/t
=d
Word problem hints:
0
1/ If an object starts from rest:
vi =
2/ If an object comes to rest:
vf = 0
3/ If the speed of an object does NOT change,
v =
vi = vf =
v
Ex. Units for speed v:
distance
units of ______________
units of speed =
time
units of ______________
[v] =
[d] / [t]
Put a rectangle around units of distance,
and an oval around units of speed:
m
cm/s
km/h
mi
1/s
ft/s
in
m/s2
mph
km
in/y
m/s
cm
h
s
km/h
rate of change in displacement
III. velocity v = time
_________________________________
=
displacement
time
a vector with the same
= ________________________________
dir. as the displacement
__________________________________
Ex: v = 55 mph, north
dir.
speed
mag. of the velocity = the ____________
velocity = ___________
speed
+ ________________
direction
arrow
Draw velocity as an _________:
55 mph
Does this show speed or velocity?
units
Note: Speed and velocity have same _________
equation
and use the same_______________:
average velocity:
Ex: Godzilla moves 5.0 x 102 meters east in
2.0 seconds. Find his average velocity.
If you assume that east is positive, you may
write this velocity as:
Physics Reference Tables, last page:
Further down, find:
units
Note: Speed and velocity have same _________
equation
and use the same_______________:
average velocity:
v = d/t
Ex: Godzilla moves 5.0 x 102 meters east in
2.0 seconds. Find his average velocity.
v = d/t
= 5.0 x 102 m, east / 2.0 s
= 250 m/s, east
If you assume that east is positive, you may
write this velocity as:
v = + 250 m/s
Ex: Mr. Siudy walks 1) 6.0 m east in 4.0 s,
then runs 2) 2.0 m west in 0.50 s. Find his
average speed in each part, and 3) the average
speed over the entire time.
1) v = d/t
= 6.0 m = 1.5 m/s
4.0 s
2) v = d/t = 2.0 m = 4.0 m/s
0.5 s
= 8.0 m
= 1.7m/s
4.5 s
total
d = the _____________
distance
3) v = d/t
Why is the average speed over the entire time
closer to the answer for part _____
?
1)
Now find the average velocities for each part of
the previous example.
displacement
d = the __________________
here
1) v = d/t
= 6.0 m, E = 1.5 m/s, E = + 1.5 m/s
4.0 s
2) v = d/t = 2.0 m, W = 4.0 m/s, W = - 4.0 m/s
0.5 s
3) v = d/t = 4.0 m, E = 0.89 m/s, E= + 0.89 m/s
4.5 s
6m
resultant
d = _______________
d:
2m
4m
less
Why is the answer to 3) now ________
than what
it was on the last slide?
IV. Uniform motion:
velocity
constant ________________
Uniform
motion
or….
speed
constant ______________
1 direction
in______________________
Ex. A car leaks oil at a constant rate while
moving to the right in uniform motion. Sketch
the pattern of drops it leaves behind.