Unit 1: Intro to Physics Speed & Velocity

when something occurs (an event) I. Time t is___________________________________ It is a _____________________________ scalar In physics, the time between two ___________ is is called the ___________________________ . The basic unit for time is the second, s . ****Other units, such as minutes, hours must usually be converted into seconds before solving any problems. events time interval

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.

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? Given: Unknown: 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

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

******Speed and velocity have same _________ and use the same_______________: units equation average velocity: Ex: A car travels 4.40 x 102 meters east in 8.0 hr. Find the car’s velocity.

Ex: Mr. McKeever 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)

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.