What is the meaning of Velocity? PHYS 102 D Physical Science Objects in Motion What is the meaning of Velocity? Zdeslav Hrepic Fort Hays State University PHYS 102 D Physical Science Supported by NSF

Objectives You will partially get involved and partially see demonstration of an activity-based method of teaching: How to interpret distance-time diagram The difference between: Instantaneous and average speed Speed and velocity Instantaneous and average velocity

Goals At the end of the activity you will be able to: Immediately utilize this method by using ready inquiry-based materials, Excel spreadsheets, digital camera and PowerPoint Animations. Become familiar with further options with video editing by using Pinacle Studio program

Material Originally developed through an NSF grant as teacher enhancement material (OPPS), later GRASPS In revision by FHSU to be used as course material Topics covered in modules divided in 5 step learning cycles Today’s cycle: What is the meaning of Velocity Word files

Average vs. Instantaneous speed Average speed is the distance traveled divided by the time to travel. Instantaneous speed is the average speed for infinitely small distances and times.

5. Graphing speed: Configuration Slow walker: Walk slow and steady. Fast walker: Walk briskly but steady. Fast starter: (Starts fast and than slows down): Run in a full sprint at the beginning. Be fast around 15m and then slow it down during the last 15m (second half of the trip). Fast finisher: (Starts slow and than speeds up): Begin with a walk, jog somewhere around 15 m and run in a full sprint by 25m.

Practical tips Begin before start Finish after the finish line Familiarize yourself with your stopwatch Fast starter: and Fast finisher: Try to achieve big difference, steady change

Spring 2005 Data Video 2

Matching Velocities – Clean data

Which v-t Graph Corresponds to the Given d-t Graph?

Which v-t Graph Corresponds to the Given d-t Graph?

Which v-t Graph Corresponds to the Given d-t Graph?

Which v-t Graph Corresponds to the Given d-t Graph?

What about the direction? Activity: Inquire 7

What about the direction? Airplanes … Speed is how fast is something going. Speed = distance crossed / time elapsed Velocity is the speed and direction of an object. Velocity is a vector (has magnitude and direction). Speed is a scalar (has magnitude only)

Speed and Velocity Moving all the time equally fast (with respect to the ground) - called? Constant speed Moving all the time equally fast and also in the same direction? Constant velocity Do we always move equally fast? Do we always move in the same direction?

Average and Instantaneous Speed Trip from home to college Things to Consider: Stop signs Traffic lights Speeds allowed What does the car speedometer measure? What is the police concerned about?

Average and Instantaneous Speed Things to Consider for the each trip: Average speed? Maximum speed? Time What is the trip choice based on? Unit conversion 2.8 mil in 5 min 1.8 mil in 6 min Video 1

Average Velocity Things to Consider: Average Velocity? Distance and Displacement Average Velocity? Avg. Velocity same or different for both trips? Avg. Velocity after returning home 2.8 mil in 5 min Straight Shot 1 mile 1.8 mil in 6 min

Average and Instantaneous Velocity Things to Consider: Average Velocity and Instantaneous Velocity 2.8 mil in 5 min Straight Shot 1 mile 1.8 mil in 6 min

Reminder (Previous cycle): Distance and Displacement START FINISH Need to distinguish how long we traveled from how far away (and in what direction) we traveled.

Distance and displacement Distance and displacement are two quantities which may seem to mean the same thing, yet have distinctly different definitions and meanings. Distance is a scalar quantity (has magnitude only) which refers to "how much ground an object has covered" during its motion. Displacement is a vector quantity (has magnitude and direction) which refers to "how far out of place an object is"; it is the object's change in position. http://www.glenbrook.k12.il.us/gbssci/phys/Class/1DKin/U1L1c.html

Direction of the Average Velocity START FINISH

Direction of the Average Velocity Displacement is a vector - Distance is not Velocity is a vector - Speed is not START FINISH

Make sense: Velocity and speed How would you determine the average speed of an object on these paths: START FINISH START FINISH Average speed vs. Average velocity

Velocity is a vector Velocity is a vector Vectors are quantities that have magnitude and direction Speed is the magnitude of a velocity.

Average vs. Instantaneous Velocity

More Information / Feedback zhrepic@fhsu.edu www.fhsu.edu/~zhrepic (www.hrepic.com) Thank You!