1. Motion Variables and Models Physics Lecture 3

2. How Far Variables Distance (d): How far an object moves disregarding its direction (scalar). Displacement (  x): How far an object moves w/ regard to its direction (vector). Examples where it makes a difference – The oval track – Confused bug Units include meters, feet, and miles

3. Check Question 1 A runner takes three laps around a 400 m track. What are the distance and displacement of the runner at the end of the run? a)1200 m, 0 m b)0 m, 1200 m c)0 m, 0 m d)1200 m, 1200 m

4. How Fast Variables Speed (v): how fast an object moves w/o regard to direction changes. – V= Total distance moved/ time interval to move Velocity (v): how fast an object moves w/ regard to direction changes. – V = displacement/time interval = x f – x i / t f – t i =  x /  t Units include meters/second, miles per hour, kilometers/hour

5. Check Question 2 What is the acceleration of a car which goes from 20 to 60 mph in 4 seconds? a)5 mph/s b)10 mph/s c)15 mph/s d)20 mph/s

6. The How Fast Fast Changes Variable Acceleration (a): How fast something speeds up, slows down or changes direction. Acceleration = (final velocity – initial velocity)/ (final time – initial time) =( V f – V i ) / (t f – t i ) =  v/  t Units of meters/second/second = m/s 2, km/hr/sec, miles/hour/second

7. Check Question 3 Which of the following controls in a car cause an acceleration? a)Gas pedal b)Brake c)Steering wheel d)Gas pedal and brake e)Gas pedal, brake and steering wheel

8. Instantaneous and Average Quantities Average quantities occur over an interval of time. – Found using equations – Average velocity, speed, acceleration Instantaneous quantities occur in 0 seconds – Found using graphs or calculus – Speedometer measures instantaneous speed – Instantaneous position, velocity and acceleration

9. Check Question 4 What is the average speed of a car that moves at 40 mph the first hour it moves and 80 mph for two more hours? a)40 mph b)60 mph c)66 mph d)80 mph

10. Motion Models Compared Constant Velocity Object moves equal displacements every second Cannot feel this motion Table Graphs Equations Constant Acceleration Object moves ever increasing or decreasing displacements every second or changes direction Can feel this motion Table Graphs Equations

11. Check Questions 5 How long will it take a car moving at a constant 80 mph to go 80 miles? How far will a car moving at a constant 60 mph go in 3 hours? A car accelerates from rest at 20 m/s/s for 3 seconds. How far does it go? How fast is it going at the end? How long will it take a car that accelerates from rest at 10 m/s/s to cover 200 m?