Relative Motion (frame of reference)

Student work sheet

An object may appear to have one motion to one observer

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)

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.

2. If you click show checkbox ,velocity vectors for your frame of reference 3. You can press the mouse button to suspend the animation. 3. There are two number near the person. Here is a demo (picture) of the program.

Suggestion from Surendranath Reddy.B.:

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, particulaly when trying to moor.

Thanks again for such an interesting web site

Best Wishes  Ray Holloway

I hope you enjoy playing with it.

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

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


1 cm 

? cm

36 m 

? m

Fish H H
Human walking 


1.4 m 

3.5 m

5 km 

12.6 km

Flying bee 5 m 18 km
Porpoise swimming 

Human racing

9 m 




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

Moon around the earth


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

Your suggestions are highly appreciated! Please click

AuthorGFu-Kwun Hwang, Dept. of physics, National Taiwan Normal University
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