Time passes. Will you? 1st atomic clock

when something occurs (an event) I. Time t is___________________________________ It is a _____________________________ scalar (no direction) In physics, the time between two ___________ is is called the ___________________________ . events time interval event 1 occurs at t = event 2 occurs at t = ti tf For example, if… initial ti = ____________ time = 5.0 s tf = ____________ time = final 8.5 s

Then the time interval: tf – ti = Dt equals Dt = tf – ti = 3.5 s 8.5 s - 5.0 s = positive The time interval will always be ______________ . In Regents Physics, instead of ________ , we use the symbol _____ for time intervals and often just call it the ____________ . Remember that _____ represents ____________________________________ . The basic unit for time is the __________________ . Other units, such as ___________________________ must usually be converted into _________________ before solving any problems. Dt t time t how long a certain process lasts second, s minutes, hours, etc seconds

How fast is Usain Bolt? What is the fastest speed possible?

II. speed v = _______________________________ =________________________________ =_________________________________ how fast an object moves time rate of change in distance a scalar (no dir., only mag.) Ex: v = 55 mph mag. Speed v can be ______________ (not changing), or it can change. If it changes, the speed at any instant is called the ____________________ speed. The ______________speed, vavg = v is: constant instantaneous average Equation for v from PRT (Physics Reference Tables):

Physics Reference Tables, last page: Further down, find:

speed v = ______________________ =____________________________________ =_____________________________________ how fast an object moves time rate of change in distance a scalar (no dir., only mag.) Ex: v = 55 mph mag. Speed v can be ______________ (not changing), or it can change. If it changes, the speed at any instant is called the ____________________ speed. The ______________speed, vavg = v is: constant instantaneous average 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 ____________ units are made up of….. derived …the 4 _____________________ (basic) units: m, A, s, kg meter, Ampere, second, kilogram fundamental

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 vf = ____________ speed = final 45 m/s  This equation is NOT in your PRT. You must _____________________ . v = (vi + vf) 2 memorize it v = (25 m/s + 45 m/s) = 35 m/s 2

How far will the car in the last example travel in 12 seconds? t = v = Given: 12 s v = d/t 35 m/s 35 m/s = d/12 s Unknown: 420 m = d d = Word problem hints: 1/ If an object starts from rest: vi = 2/ If an object comes to rest: vf = 3/ If the speed of an object does NOT change, v = vi = vf = v

Ex. Units for speed v: units of ______________ units of speed = [v] = 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 distance time [d] / [t]

III. velocity v = _________________________________ time rate of change in displacement displacement = time = ________________________________ __________________________________ a vector with the same dir. as the displacement Ex: v = 55 mph, north dir. mag. of the velocity = the ____________ speed velocity = ___________ + ________________ speed direction Draw velocity as an _________: arrow 55 mph

Does this show speed or velocity?

Note: Speed and velocity have same _________ and use the same_______________: units equation 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:

Note: Speed and velocity have same _________ and use the same_______________: units equation 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 4.0 s = 1.5 m/s = 2.0 m 0.5 s 2) v = d/t = 4.0 m/s = 8.0 m 4.5 s 3) v = d/t = 1.7m/s d = the _____________ distance total 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. d = the __________________ here displacement 1) v = d/t = 6.0 m, E 4.0 s = 1.5 m/s, E = + 1.5 m/s 2) v = d/t = 2.0 m, W 0.5 s = 4.0 m/s, W = - 4.0 m/s 3) v = d/t = 4.0 m, E 4.5 s = 0.89 m/s, E = + 0.89 m/s 6 m d = _______________ d: resultant 2 m 4 m less Why is the answer to 3) now ________ than what it was on the last slide?

IV. Uniform motion: constant ________________ velocity Uniform motion or…. constant ______________ in______________________ speed 1 direction 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.