Measuring Motions Speed Velocity and Acceleration 91818 WHAT

Measuring Motions: Speed, Velocity, and Acceleration 9/18/18

WHAT IS MOTION? � Motion is when an object changes place or position. To properly describe motion, you need to use the following: https: //www. youtube. com/watch? v=21 Bw. UNDOQno • • Start and end position? Movement relative to what? How far did it go? In what direction did it go?

SPEED How can we describe how fast an object moves? Example: A car on Beltway 8 travels 90 km in 1 hour. We say that the car travels at a speed of 90 km/hr.

CALCULATING SPEED � Speed (S) = distance traveled (D) / the amount of time it took (T). S = d/t https: //www. youtube. com/watch? v=_Dt. DCBHEM 1 k

CALCULATING SPEED S = d/t � If I travel 100 kilometer in one hour then I have a speed of… � 100 km/h � If I travel 1 meter in 1 second then I have a speed of…. � 1 m/s

GRAPHING SPEED � Speed is usually graphed using a line graph, and it depicts the distance and time. • Time is the independent variable, and thus is ALWAYS on the x-axis. • Distance is the dependent variable, and is ALWAYS on the y-axis.

GRAPHING SPEED: DISTANCE VS. TIME GRAPHS Denver Phoenix

UNITS FOR SPEED � Depends, but will always be a distance unit / a time unit � Ex. Cars: mi. /h = Miles per hour � Jets: km/h = Kilometers per hour � Snails: cm/s = Centimeters per second � Falling objects: m/s = Meters per second

How can we describe how fast an object moves? Speed is a measure of how fast something moves. Speed = distance travelled per unit of time SI unit: m/s or km/h (for long distances)

QUESTION 1 �A bug crawls 10 cm in 5 sec. What was the bug’s approximate speed in cm/sec? 2 cm/sec

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.

AVERAGE SPEED � Speed is usually NOT CONSTANT � Ex. Cars stop and go regularly � Runners go slower uphill than downhill � Average speed = total distance traveled/total time it took.

CALCULATING AVERAGE SPEED � � A car travels 300 km in 6 hours. What is the average speed of the car in km/hr? Distance: � � Time: � � 300 km 6 hr Ave. Speed: � s=d/t = 300 km/6 h = 50 km/h

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 time of travel

QUESTION The world record for women’s 100 -m race is 10. 49 s. What is the average speed? Average speed = ( 100 m ) 10. 49 s = 9. 53 m/s

QUESTION � What is the speed of a jet plane that flies 7, 200 km in 9 hr ? � A) 64, 800 km � B) 800 km � C) 7, 191 km � D) 7, 209 km � Ave. Speed: � s=d/t = 7200 km/9 h = 800 km/h

INSTANTANEOUS SPEED Instantaneous speed = speed at any instant The word ‘speed’ alone instantaneous speed Instantaneous speed distance travelled in an extremely short time interval

INSTANTANEOUS SPEED Speedometer tells the car’s speed at any instant!

https: //www. youtube. com/watch? v=apew. Lk. LAR-U VELOCITY � Velocity – the SPEED and DIRECTION of an object. � Example: � An airplane moving North at 500 mph � A missile moving towards you at 200 m/s

VELOCITY Velocity is. . . a speed in a given direction or rate of change of displacement. direction velocity magnitude (speed) a vector quantity

Velocity SPEED WITH DIRECTION Train engineers use speed only. speed = 90 km/h Pilots use velocity (direction & speed). speed = 300 km/h direction = west

AVERAGE VELOCITY overall displacement Average velocity = total time of travel direction of overall direction of velocity = displacement

QUESTION �A student runs around a circular track that is 1000 m 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.

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 � Which of these is a correct velocity? A. B. C. D. 55 miles per hour 15 kilometers per second 30 meters per second east 400, 000 meters per hour

QUESTION � What is the difference between speed and velocity? � Speed is just distance/time. Velocity includes speed & direction as well. https: //www. youtube. com/watch? v=uk. Wp. TQq 13 dw

QUESTION � How can you determine an object’s speed and velocity? � You can determine speed by using a meter stick and a stopwatch, and the determination of velocity requires a meter stick, stopwatch, and compass.

QUESTION Average Speed = Total distance/Total time = 12 km/6 hr = 2 km/hr � Below is a distance vs. time graph of my position during a race. What was my AVERAGE speed for the entire race? Distance=12 km Time = 6 hr

QUESTION � Below is a distance vs. time graph for 3 runners. Who is the fastest? Leroy is the fastest. He completed the race in 3 hours

ACCELERATION � Acceleration = speeding up � Acceleration – the rate at which velocity changes � Can be an: � Increase in speed � Decrease in speed � Change in direction https: //www. youtube. com/watch? v=vx. FYfum. AAl. Y

ACCELERATION When an object moves faster and faster, its speed is increasing (velocity changed).

ACCELERATION When an object moves slower and slower, its speed is decreasing (velocity changed).

ACCELERATION When an object changes direction, its velocity changes too.

ACCELERATION � The � formula for calculating acceleration is: Acceleration (a) = final velocity (vf) – initial velocity (vi) � � The time (sec) unit for acceleration, in this case, is m/s/s OR m/s 2

ACCELERATION Acceleration measures the change in velocity direction speed Acceleration = velocity per unit time overall change in velocity = total time taken Unit: m/s/s = m/s 2 vector quantity

TYPES OF ACCELERATION � Increasing � Example: speed Car speeds up at green light � Decreasing � Example: � Changing screeeeech Car slows down at stop light Direction � Example: speed) speed Car takes turn (can be at constant

QUESTION Tommy accelerates from 20 m/s at 15 sec (t 1) to 40 m/s at 60 sec (t 2). What is his avg. acceleration between t 1 and t 2? Avg. acceleration 40 m/s – 20 m/s = = 60 s – 15 s 45 s =. 44 m/s 2

QUESTION � How can a car be accelerating if its speed is a constant 65 km/h? � If it is changing directions it is accelerating

GRAPHING ACCELERATION � Can use 2 kinds of graphs � Speed vs. time � Distance vs. time

GRAPHING ACCELERATION: SPEED VS. TIME GRAPHS 1)Speed is increasing with time = accelerating 2)Line is straight = acceleration is constant

GRAPHING ACCELERATION: DISTANCE VS. TIME GRAPHS 1)On Distance vs. Time graphs a curved line means the object is accelerating. 2)Curved line also means your speed is increasing.

SPEED/VELOCITY/ACCELERATION Speed=Distance ÷ Time � Time=Distance ÷ Speed � Distance = Speed X Times � https: //www. youtube. com/watch? v=8 glf. UANj. Bb. Y Velocity=Distance ÷ Time � Time= Distance ÷ Velocity � Distance=Time X Velocity � https: //www. youtube. com/watch? v=Rl. Fg. R 297 o 8 I Acceleration=Velocity ÷ Time � Time= Velocity ÷ Acceleration � Velocity=Time X Acceleration �