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 ˇV 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 referenceGroundPersonRiverBoat
Object color codeGrayBluedark GreenRed

Program Note:

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/sm/sm/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/s0.0 m/sm/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/sm/sm/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 ˇV Press the ˇ§Refreshˇ¨ 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 ˇK
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 = GroundRiverBoat 
Personˇ¦s Horizontal Velocity 
When on the GROUND
m/sm/sm/s
Personˇ¦s  Vertical Velocity 
When on the GROUND
m/sm/sm/s
Personˇ¦s Horizontal Velocity 
When in the WATER
m/sm/sm/s
Personˇ¦s  Vertical Velocity 
When in the WATER
m/sm/sm/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 ˇV 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.