Time passes. Will you?

1. Time passes. Will you? 1st atomic clock

2. 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 final tf = ____________ time = 8.5 s

3. Then the time interval: tf – ti = Dt equals 3.5 s Dt = tf – ti = 5.0 s = 8.5 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

4. Before the 1900s, it was thought that everyone measured the same time interval. "1 second" of time spent on rocket Earth …does NOT equal 1 second of time for a stationary observer Now we know this is NOT true! Relative motion and even gravity affect time. Einstein figured this out.

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

6. Ahead, warp factor 9, Scotty…

7. 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. 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):

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

9. how fast an object moves v speed v = ______________________ =____________________________________ =_____________________________________ 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): = d/t

10. 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….. …the 4 _____________________ (basic) units: m, A, s, kg meter, Ampere, second, kilogram fundamental

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

12. t = v = v v How far will the car in the last example travel in 12 seconds? = d/t Given: 12 s d/12 s 35 m/s 35 m/s = 420 m = d Unknown: 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 = 0 0 vf = vi =

13. Ex. Units for speed v: units of ______________ units of speed = units of ______________ [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]

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

15. Does this show speed or velocity?

16. 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:

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

18. Note: Speed and velocity have same _________ and use the same_______________: v v v units equation = d/t average velocity: Ex: Godzilla moves 5.0 x 102 meters east in 2.0 seconds. Find his average velocity. = 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: = + 250 m/s

20. = d/t = d/t = d/t v v v Ex: Ms. Rudd walks 1) 6.0 m east in 4.0 s, then runs 2) 2.0 m west in 0.50 s. Find her average speed in each part, and 3) the average speed over the entire time. 1) = 1.5 m/s = 6.0 m 4.0 s = 2.0 m 0.5 s 2) = 4.0 m/s = 8.0 m 4.5 s 3) = 1.7m/s total d = the _____________ distance Why is the average speed over the entire time closer to the answer for part _____ ? 1)

21. = d/t = d/t = d/t v v v Now find the average velocities for each part of the previous example. displacement d = the __________________ here 1) = 6.0 m, E 4.0 s = + 1.5 m/s = 1.5 m/s, E 2) = 2.0 m, W 0.5 s = 4.0 m/s, W = - 4.0 m/s 3) = 4.0 m, E 4.5 s = 0.89 m/s, E = + 0.89 m/s 6 m resultant d = _______________ d: 2 m 4 m less Why is the answer to 3) now ________ than what it was on the last slide?

22. IV. Uniform motion: velocity constant ________________ 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.