# Know what is relative?

1. Apr 28, 2010

I heard many people telling this is relative to something, it moves relatively... and so on

I wanted to know what is relative?

What does it mean?

How is it used?

They tell that time is relative?

What does that mean?

2. Apr 28, 2010

### ansgar

Re: Relative?

it means that two observers will not not agree upon how long time has elapsed between to events, and on lengths.

you sit on a train that goes very fast according to me, but according to you - it is ME who travels fast! If you and I would measure motion on this train, such as a ball being thrown, we will not agree upon the dynamics of the ball.

3. Apr 28, 2010

### Tac-Tics

Re: Relative?

In physics, there are a few distinct uses for the word "relative".

Essentially, relative is used to contrast with absolute. If something is relative, you need to pick a reference point to measure it. Two people measuring the same thing at the same time will get different values unless they are using the same reference point.

The most common example has been known since Galileo. We call it Galileian relativity. The idea is speed is relative. When you're standing still on a sidewalk, a car zooms past you at 50 miles per hour. However, if you are traveling in that car, the car appears to be still and a man on the sidewalk is the one flying at 50 miles per hour.

Similarly, if you are traveling in a car, and you accidently rear-end the car in front of you, the amount of damage isn't determined by your speed relative to the road (~50 mph). Instead, it's determined by your speed relative to the other car (~2 or 3mph).

Einstein extended Galileian relativity in the early 20th Century, accounting for a strange property of light (that it always moves at the same speed regardless of your reference point). Some other consequences of Einstein's theory of special relativity are that not only velocity, but also distances, time spans, and simultaneous-ness are "relative" properties.

4. Apr 28, 2010

### LostConjugate

Re: Relative?

"He is relatively wealthy"

If a clock measures time by moving parts and the collection of parts are moving relative to you the clock is going to register a different time than a clock that is not moving relative to you. All clocks measure time by moving parts, including sundial/solar system clocks. So time is relative.

Since a human is made of moving parts if they moved fast enough relative to earth they could out live all other humans on earth.

Last edited: Apr 28, 2010
5. Apr 29, 2010

Re: Relative?

In what types of situations can it be used?

if I'm relative to something what will it mean?

6. Apr 29, 2010

### ansgar

Re: Relative?

in physics, we use "relative motion"

you can not just say "I am relative him" etc... it has no meaning, one must specify what PROPERTY is relative, not just WHOM

7. Apr 29, 2010

Re: Relative?

ok

but for what reason is relative used?

Why?

8. Apr 29, 2010

### ansgar

Re: Relative?

relative WHAT?

relative motion is "used" since that is what happens in nature, things move relative each other all the time!

9. Apr 29, 2010

Re: Relative?

"things move relative each other all the time! "

I don't understand the word 'relative'

if you wouldn't used the word relative how would you explain that phrase to me?