Student work sheet (word)

An object may appear to have one motion to one observer

and a different motion to a second observer,

depending on how the two observers are moving with respect to one another.

This java applet let you view objects from different frame of reference.

Imaging there is a river in the center of the screen (yelow dots are moving with water)

a red boat is also moving with respect to the river,
There is a person(blue) walks close to one side of the river, (S)he can swim across the river.

You can easily change frame of reference by moving your mouse to different regions.

e.g. If you move your mouse within the river,
YOU will becomes an observer moving with water.

If you move your mouse into the boat region,

You becomes on the boat watching other objects moving.

You can walk along with that person, or just standing there on the ground.

Try to move the mouse at different regions!
We will do something more complicate later!
 frame of reference Ground Person River Boat color code Gray Blue dark Green Red
2. If you click show checkbox ,velocity vectors for your frame of reference
will be shown with numbers. Its color is determined by the above color codes.
3. You can pressthe mouse button to suspend the animation.
If you press with left mouse button, animation will resume when you release it.

If you press with right mouse button, you need to click it again.

How to change the velocity vectors?

Just click near the tip of the arrow, and drag it left and right.
Please try it first! Then, we will do something more interesting!
3. There are two number near the person.
Those are vertical and horizontal speed of that person at your frame of reference.

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.
Click with right mouse button to resume the animation,
That person will move toward the river, then, swim across the river.

(The horizontal speed with respect to ground will increase due to river current)

Now, try it! And watch (her)him at different frame of references.
Here is a demo (picture) of the program.

Suggestion from Surendranath Reddy.B.:

add a square powered moving object,
and a smll ball(yellow) moving between object's two ends.
click and drag the tip of velocity vector (while animation is suspended)
to change it.
In order to demonstrate 2D relative motion, a 2D checkbox were added.

Click the 2D checkbox and a ball will be thrown upward from the above moving object.

The trajectory of the ball(blue) will be shown for you.

Subject: Re: Reaction time & car accident
Date:    Mon, 25 Oct 1999 20:33:42 +0100
From:    "Ray Holloway"
To:      "Fu-Kwun Hwang"

I am now studying the Relative Motion applet, it is most interesting to see clearly the things we notice in everyday life.I have had some holidays boating on rivers and I can picture the effects clearly as I use the applet.While driving a boat it's speed relative to the current is most apparent, particularly when trying to moor.

Thanks again for such an interesting web site

Best Wishes  Ray Holloway  ray@middx.screaming.net

I hope you enjoy playing with it.

Those numbers at the left side are object's horizontal coordinates,

and you also know the timing.
Why not copy those numbers (while animation is suspended) and make a plot out of it.

Are you going to do it?

Typical Speeds (Some numbers are left blank for you to make a good quest,OK!¡^

 Motion distance travels in one second distance moves in one hour Swimming sperm 45 um (=10-6m) 16.2 cm snail 1.5 mm (=10-3m) 5.4 m ant turtle 1 cm ? cm 36 m ? m Fish ¡H ¡H Human walking running 1.4 m 3.5 m 5 km 12.6 km Flying bee 5 m 18 km Porpoise swimming Human racing 9 m ¡H 32.4km ¡H Running cheetah 29 m 104 km Falcon in a dive 37 m 133 km automobile(max.) 62 m 223 km commercial jet airline 267 m 961 km sound (in air) 340 m 1224 km surface on the earth near equator 460 m 1.65 106 m SR-71reconnaissance Moon around the earth 980 1000 m 3528 km 3.6 106 m Earth around the Sun 29 km 1.04 108 m Earth-Sun travel around ore galaxy 210 km 7.56 108 m light 3 108 m 1.08 1012 m