Speed, Velocity, and Acceleration PDF

Speed, Velocity and Acceleration 1 Both Mr Rabbit and Mr Tortoise took the same round trip, but Mr Rabbit slept & returned later.  Who runs faster? No, I travelled Me, as I spent more distance less time on every the...

Speed, Velocity and Acceleration 1 Both Mr Rabbit and Mr Tortoise took the same round trip, but Mr Rabbit slept & returned later.  Who runs faster? No, I travelled Me, as I spent more distance less time on every the trip. second I ran. Who is right? 2 Some kid is lost in the woods. (a) If he walks at a speed of 4 km/hr, try to locate his possible positions on the 2 Some kid is lost in the woods. (b) What else is important to find the kid? The direction in which he has been walking. Reference Points  All Motion is relative All motion is relative to a reference. This means that we describe motion of an object relative to some other object  All Motion is relative In our environment, the reference for motion is the earth’s surface, and speeds are measured relative to the earth The earth moves at 107,000 km/h relative to the sun Calculating Motion and Speed  1 Speed How can we describe how fast an object moves? E.g. A car on Beltway 8 travels 90 km in 1 hour. We say that the car travels at a speed of 90 km/hr.  1 Speed How can we describe how fast an object moves? Speed is a measure of how fast something moves. Speed SI unit: = distance travelled per unit of time or km/h (for long m/s distances) 1 Spee d a Average speed A car travels at 50 km/h, slows down to 0 km/h, and speeds up again to 60 km/. Its average speed over the whole journey overall distance = travelled total  Question 1 A bug crawls 10 cm in 5 sec. What was the bug’s approximate speed in cm/sec? 2 cm/sec 1 Spee d a Average speed Average speed does not tell the variations during the journey. On most trips, the speed at any instant is often different from the average speed. 1 Spee d b Instantaneous speed Instantaneous speed = speed at any instant The word ‘speed’ alone spee  Instantaneous instantaneous d  distance travelled in an extremely speed short time interval 1 Spee d b Instantaneous speed Speedometer tells the car’s speed at any instant!  Question 2 The world record for women’s 100-m race is 10.49 s. What is the average speed? ) Average speed ( 100 10.49 = m s = 9.53 m/s Velocity  2 Velocity Velocity is... a speed in a given direction or rate of change of displacement. velocit direction a y vector magnitu quantit y de (speed) 2 Velocit y a Speed with direction Train engineers use speed only. speed = 90 km/h Pilots use velocity (direction & speed). speed = 300 2 Velocit y b Average velocity overall Average velocity = displacement total time of travel direction of direction of velocity displaceme = overall nt  Question 3 A student runs around a circular track that is 1000m in length in a time of 30 min. What is the average velocity of the student? 0 m/min If the student runs completely around the track, they are back where they began. So their overall displacement is zero.  2 Velocit y c Instantaneous velocity The velocity at any instant is called instantaneous velocity. If a car moves at a constant velocity... … its average and instantaneous velocities have the same value.  Question 4 Which of these is a correct velocity? A. 55 miles per hour B. 15 kilometers per second C. 30 meters per second east D. 400,000,000 meters per hour Acceleration  3 Acceleration When an object moves faster and faster, its speed is increasing (velocity changed).  3 Acceleration When an object moves slower and slower, its speed is decreasing (velocity changed).  3 Acceleration When an object changes direction, its velocity changes too.  3 Acceleration Acceleration measures the change in velocity directio spee n d Acceleration = velocity per unit time = overall change in Unit: = velocity total vector m/s/s quantity m/s2time taken  3 mean? Acceleration If a car accelerates at 2 m s , what does that –2 t= v=0 0 t = 1 s v = 2 m s–1, v = 2 m s–1 1 m t=2sv v– = 2 m s–1 3 =4ms m 1, t=3s v = 6 m s– 5 1, m v = 2 m s–  Question 5 Tommy accelerates from 20 m/s at 15 sec (t1) to 40 m/s at 60 sec (t2). What is his avg. acceleration between t1 and t2? Avg. acceleration 20 = 40 m/s – 20 = m/s m/s =.44 45 s 60s – 152s m/s