NTNUJAVA Virtual Physics Laboratory

Subject: Relative motion
Date:    Fri, 29 Oct 1999 16:32:03 -0500
From:    "Gary Richert" <grichert@sun.hazelwood.k12.mo.us>
To:      <hwang@phy03.phy.ntnu.edu.tw>

Hi,

I love your relative motion website.
I have attached a word document thatwill allow my students to work with your motion applet.
I have yet to test the document with the students.
Please let me know of any errors you find or suggestions to add tothis document.
You may alter it in any way and share it with others who may visityour web page.
Thanks for the useful class room tool.

Gary Richert
Science Teacher
Florissant, Mo.
USA
grichert@stlnet.com

---

Name ________________________________________ Hour _____

Relative Motion
A look at "Frames of Reference"
http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=227

Introduction
An object may appear to have one motion to one observer and a differentmotion to a second observer, depending on how the two observers are movingwith respect to one another.
This java applet let you view objects from different frames of reference. Imaging there is a river in the center of the screen (yellow dots are movingwith water ¡V green area) a red boat is also moving with respect to theriver. There is a person (blue) walking close to one side of the river,(S)he can swim across the river.  You can easily change frame of referenceby moving your mouse to different regions.  e.g. If you move yourmouse within the river, YOU will become an observer moving with water. If you move your mouse into the boat region, You are on the boat (boatis your frame of reference and the boat appears to you to be at rest!)watching other objects that have motion.  The object that is theframe of reference has a velocity of 0.0 m/s.

Frame of Reference Chart
 

frame of reference	Ground	Person	River	Boat
Object color code	Gray	Blue	dark Green	Red

Program Note:

•  You can press the mouse button to suspend the animation.
•  If you press with left mouse button, animation will resume when yourelease it.
•  If you press with right mouse button, you need to click it againto resume animation.

The velocity vector arrows shown do not remain the same colors.  Whenthe ground is the frame of reference the vector arrow is BLACK.  Whatarrow color is used for the other frames of reference?  Fill in thechart below:
 
 
 

Frame of Reference	Ground	Person	River	Boat
Vector Color Code(Arrow Color)	Black

 
 

Click on the Info box at the top of the Applet.   Place yourmouse arrow on the ground and click your right mouse button.  Determinethe relative speed of the man, river, and boat.  Record these valuesin the data table.
Observation #1

Frame of Reference is the GROUND
 
 

Frame of Reference	Ground	Person	River	Boat
Relative Speed	0.0 m/s	m/s	m/s	m/s

 

Click the right mouse button to resume the animation.

Observation #2
Place your mouse arrow on the river and click your right mouse button. Determine the relative speed of the ground, man, and boat.  Recordthese values in the data table.

Frame of Reference is the RIVER

Frame of Reference	Ground	Person	River	Boat
Relative Speed	m/s	m/s	0.0 m/s	m/s

 

Analysis:
 How much velocity change (dV) occurred to the ground, man, riverand boat when the frame of reference was switched from the ground to theriver? dV =  ________________

 What factor determines the velocity (speed and direction) measuredof an object?
 
 

 When stating the speed of an object on earth, what is the frameof reference commonly used by observers?  ___________________________________

How to change the velocity vectors?
Press the right mouse button to suspend the animation.  Now clicknear the tip of the vector arrow, and drag it left or right.  Thisprocedure can be used on ground, river, man, or boat to change their velocity.
Observation #3   The Motion of an Object is Relative
With the mouse cursor on the ground (gray area) click your right mouseto stop the animation. Place your mouse arrow on the boat vector and click-and-Dragthe boat vector so that it has a velocity of 0.0 m/s (negative values indicatesthe direction is upstream). Click the right mouse button to resume theanimation.
Determine the relative speed of the boat when the mouse cursor is onthe river, ground, boat and man.  Record these values in the datatable.
 

Frame of Reference is the RIVER

Frame of Reference	Ground	Person	River	Boat
Boat Speed	m/s	m/s	m/s	m/s

Analysis:
The speed of the boat is not the same from each frame of reference. True or False?
From what frame(s) of reference is the boat stationary?  __________________________
From what frame of reference(s) is the boat moving with negative velocity?______________________________________________________________________________
From what frame of reference(s) is the boat moving with positive velocity?______________________________________________________________________________

Observation #4   The Motion of Person in Two Dimensions

Refresh the webpage ¡V Press the ¡§Refresh¡¨ button at the top or themonitor screen.
 Notice there are two number near the person (0.0 and 5.0). Those are vertical and horizontal velocity of that person at your frameof reference.  The vertical velocity is 0.0 m/s and the horizontalvelocity is 5.0 m/s.  (Positive values indicated the direction isto the right and down on the monitor screen, negative values indicate thedirection is up or left on the screen.)

While the animation is suspended :
Click near the left leg of that person and drag the mouse up and down,you are changing her (his) vertical speed.  Set the vertical motionto +10 m/s and the horizontal speed to 0.0 m/s.  Place the mouse cursorarrow on the ground and ¡K
Click with right mouse button to resume the animation,

That person will move toward the river, then, swim across the riverand return to the ground.  The motion is repeated as the animationruns.
Record the vertical and horizontal velocity of the man on ground andin the water from each of these frames of reference.

frame of reference =	Ground	River	Boat
Person¡¦s Horizontal Velocity  When on the GROUND	m/s	m/s	m/s
Person¡¦s  Vertical Velocity  When on the GROUND	m/s	m/s	m/s
Person¡¦s Horizontal Velocity  When in the WATER	m/s	m/s	m/s
Person¡¦s  Vertical Velocity  When in the WATER	m/s	m/s	m/s

  1. When does the person have only a vertical speed? ___________________________________
Why is the horizontal speed = 0.0 m/s? ____________________________________________

2.When does the person have a vertical and horizontal seed? ____________________________

3. When is his horizontal speed negative?  ____________ Why isit negative? _______________
 
 
 
 
 

Observation #4   Two Dimension Relative Motion ¡V Launchinga Projectile

In order to demonstrate 2D (two dimensional) relative motion, a 2D checkboxwere added.

Refresh the web page again.

Part A) Click the right mouse button to suspend the animation. Click the 2D checkbox.  Place the mouse cursor on the ground and clickthe right mouse button to resume the animation.   Notice a ballwill be thrown upward from the barge moving in the river. Your frame ofreference is the ground.
The trajectory of the ball (blue) will be shown to you from the frameof reference of the ground.
Describe the trajectory of the ball seen on the screen.  _____________________________
Where does the ball land when it falls? _________________________________________
Does the ball have motion in two dimension (vertical and horizontal)?________________
What do you observe to be the velocity of the barge?  ______________________________
What do you observe and conclude the horizontal velocity of the ballmust be? __________

Part B.  Refresh the webpage again.
Click the right mouse button to suspend the animation.  Clickthe 2D checkbox.  Place the mouse cursor on the River and click theright mouse button to resume the animation. Your frame of reference isnow the river.
The trajectory of the ball (blue) will be shown to you from the frameof reference of the river.
Describe the trajectory of the ball seen on the screen.  _____________________________
Where does the ball land when it falls? _________________________________________
Does the ball have motion in two dimension (vertical and horizontal)?________________
What do you observe to be the velocity of the barge?  ______________________________
What do you observe and conclude the horizontal velocity of the ballmust be? __________
 

Part C.  Refresh the web page again.
Click the right mouse button to suspend the animation.  Clickthe 2D checkbox.  Place the mouse cursor on the boat and click theright mouse button to resume the animation.   Notice a ball willbe thrown upward from the barge moving in the river. Your frame of referenceis the boat.
The trajectory of the ball (blue) will be shown to you from the frameof reference of the ground.
Describe the trajectory of the ball seen on the screen.  _____________________________
Where does the ball land when it falls? _________________________________________
Does the ball have motion in two dimension (vertical and horizontal)?________________
What do you observe to be the velocity of the barge?  ______________________________
What do you observe and conclude the horizontal velocity of the ballmust be? __________
 

Summarize the Main Ideas you learned in this virtual lab regarding howthe description of   motion depends on the frame of reference.

You need to open the html file with your browser. (check out relativeVelocity.html)
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You used to be able to drag the velocity vector up or down also to show relative velocity at right angles.  Can this still be done?  If not, can you make it so that it can??  Thanks

I love to see this stuff being shared. I had to do this exercise hundreds of times a day at sea in the Coast Guard using paper maneuvering boards available in packets of 100, or on a round 3' diameter plastic maneuvering board called a Surface Summery Plotter. First, we would graphically display our ships course and speed on the SSP or maneuvering board, then using the radar, we would plot the bearing and range of a surface contact at a 3 minute interval, measure the distance traveled, divide by 100
which produced the speed of relative motion. Parallel that line till it intersected your displayed ship's speed on the graph, graphically display the other ship's relative speed on his relative motion line and the other ship's true or magnetic course and speed would be shown on the graphic display. Once we learned the other ship's course and speed, we could set up courses to intercept it within a certain time frame, at a certain speed or avoid by a certain distance at a certain time. We also used this method for search and rescue patterns using aircraft and helicopters, and intercepting rain squalls in the south pacific to provide showers for the crew when the evaporator wasn't working right. I also taught this course at Officer Candidate School and Boatswain Mate School. What a trip. If anyone has access to a Coast Guard cutter, I'm sure they would share a paper maneuvering board. 

? thanks