Honors Physics Chapter 2 Kinematics in One Dimension Kinematics – deals with concepts describing motion Dynamics – deals with the effects that forces have on motion Mechanics – Kinematics and Dynamics make up the branch of physics called Mechanics Displacement: It is a vector showing the initial position and final position of an object. (SI unit: meter) Velocity is speed + direction A plane flies at 100 mph from Minneapolis To Chicago (a distance of 325 miles). How Long will the flight take to get there? 3250 minutes .31 hours 3 hours and 15 minutes 3 hours and 25 minutes 2 hours and 45 minutes Speed = distance time

Kinematics One Dimension Average Velocity = displacement / elapse time or total distance / total time Instantaneous Velocity = Your speed and direction at any given moment in time. The space shuttle travels at 7,600 m/s. You start and stop a stopwatch as quickly as you can and get .05 sec. About how many football fields (96m) can the space shuttle travel in the time it takes you to start and stop a stopwatch? A) 1 B)2 C) 3 D) 4 E) 5 F) 8 G) 11 H) 14

Acceleration If you can “feel it” it’s acceleration It is the rate of change in velocity Speeding up, slowing down, changing direction It is how much is your speed changing each second meters / seconds / second m/s2 Acceleration = Vfinal – Vinitial time If a baseball goes from 0 – 50 m/s In half a second. What is the acceleration Of the baseball? 100 m/s2 0 m/s 200 m/s2 100 m/s 125.5 m/s2

10 m/s B) -25 mi/hr/sec C) 25 mi/hr/sec A car on the highway is going 50 miles/hr and passes another car and reaches a top speed of 75 mi/hr 5 seconds after beginning the pass. What is the rate of acceleration of the car? 10 m/s B) -25 mi/hr/sec C) 25 mi/hr/sec D) 5 m/s2 E) 5 mi/hr/sec F) 10 m/s2 A car going 20 m/s (about 45 mph) is put into neutral and coasts to a complete stop. You have an accelerometer in the car and it shows you are decelerating at a rate of - 2 m/s2. How long does it take for the car to slow down to a speed of 10 m/s (22 mph)? A)1 sec B) 2 sec C) 5 sec D) 10 sec E) 40 sec

Gravity Galileo Galilee – Experimented with dropping different massed objects off the Tower of Pisa. All objects fall at the same rate, regardless of mass – 9.8 m/s2 Isaac Newton – He did experiments that showed all Things with mass have gravity. Anything with mass has a gravitational pull The larger the MASS of an object, the larger the gravitational pull The closer you are, the greater the “g”

Gravity Albert Einstein – Explained why there is gravity through his ideas of space and time. Objects with mass bend the “fabric” of space/time and create an attraction of other objects.

Motion is relative Anything in motion has a right to say it is at rest It depends on your frame of reference

Calculating Free Fall How fast an object is falling: Velocity = Gravity x Time v = gt How far an object falls: Distance = ½ gt2 You are standing on top of your 6 meter spaceship on the moon (gravity: 2 m/s2). You drop something off the spaceship. How long does it take to hit the ground? A) .5 s B) 1 s C) 1.5 s D) 2 s E) 2.5 s F) 3 s

A penny is dropped from the top of the IDS Tower in Minneapolis (236 m). A penny is also dropped from the Sears tower in Chicago (442 m). Ignoring air resistance, how much faster is the penny dropped from the Sears Tower going when it hits the ground than the IDS tower penny. Sears Tower 12.4 m/s 25 m/s 68 m/s 93 m/s 164 m/s 212.4 m/s I don’t know how to solve this IDS Tower

How fast an object is going with an initial velocity is expressed as: If an object has in initial velocity going up or down as it goes into freefall, the equation changes just a little. How fast an object is going with an initial velocity is expressed as: Velocity = Velocityinitial + gravity x time V = V0 + gt A ball is thrown upward at 15 m/s. How fast is it going after 2 seconds? 4.6 m/s B) -4.6 m/s C) neither of these

How far an object goes that has an initial velocity is expressed as Distance = Velocityinitial x time + ½ gravity x time2 d = V0t + ½ gt2 A ball is thrown upward at 15 m/s. How high is it after 2 seconds? About… 5m B) 8m C) 10m D) 12 m

Kinematic Equations The equations used for freefall can also be used in lateral motion, substituting “g” for whatever acceleration is present. In summary, these equations can solve any straight line motion: V = V0 + at X = ½ (V0 + V) t X = V0t + ½ at2 V2 = V02 + 2ax

Air resistance Responsible for changes in rates of falling objects A form of friction that gives off heat. When air resistance is negligible, objects can be considered “free falling”

Motion graphs Which stage is the object stopped? Where is the object accelerating? What stage shows a constant speed? What would the graph look like if the object moved backward at Stage 6?

Questions Punter Chris Kluwe of the Vikings has a hang time of 4 seconds on a punt. How high does it go? A) 10m B) 20m C) 30m 80m 160m How long does it take for a water Balloon to fall to ground from 15meters (about 5 stories) A) 1.7 sec B) 3 sec C) .86 sec D) 4.7 sec

Questions A rocket is launched upward and reaches a velocity of 200mph at the moment the engine quits. What is the approximate velocity of the rocket at 1 second after the engine went out (#2)? 0 mph 198 mph 200 mph 202 mph