another phys question...

[americanjebus]

when we say that motion is relative, what is it relative to? whats an example?

srry my book neglected to mention it.

 

[Dirgle]

Relative to the observer or to some fixed object. A car is in motion relative to the road, or to the cop standing on the side of the road with the radar detector.

 

[GrimJack]

Exactly. Consider that the cop, standing by the side of the road, is still speeding along as the earth rotates on it's axis, plus orbits the sun, the entire solar system is rotating around the galactic core, and the entire universe is expanding outwards at an incredibly fast rate.

 

[SupraMario]

the entire universe is expanding outwards at an incredibly fast rate.

just to throw this in there, thats a theory, most everything about space is.:biglaugh:

 

[souprat]

you could also think of it like you car could be standing still, and the cop is doing 75mph past you. try to write the cop a ticket next time you get pulled over.

 

[americanjebus]

that was to easy, i got it after i posted it, just wait.

 

[lanky189]

just to throw this in there, thats a theory, most everything about space is.:biglaugh:

actually it is FACT that the universe is expanding, the theory is whether or not it will contract back.


also.. using the radar gun idea.. if a cop is travelling at 55mph behind you and laser guns your car at 10mph that means you are travelling at 65mph.. however relative speed (to the cops speed gun) is only 10mph..


make sense?

 

[Idealsupra]

damn....ya'll are smart............


i said BROWN.











10 pts to who can tell me what thats from

 

[Shawndude]

also.. using the radar gun idea.. if a cop is travelling at 55mph behind you and laser guns your car at 10mph that means you are travelling at 65mph.. however relative speed (to the cops speed gun) is only 10mph..make sense?

What if you're going 55mph and the cop 65mph? Will the radar show the same 10 mph? Does the radar show +/- on the display? Just curious.

...

As for the word "theory" the scientific definition of "theory" is nothing like what the everyday usage is. It is million miles away from the crock-pot "theories" people throw out while tripping on LSD or imagining pink elephants in their closets.

Copy pastage goodness: http://encyclopedia.laborlawtalk.com/Theory

In common usage a theory is often viewed as little more than a guess or a hypothesis. But in science and generally in academic usage, a theory is much more than that. A theory is an established paradigm that explains all or many of the data we have and offers valid predictions that can be tested. In science, a theory can never be proven true, because we can never assume we know all there is to know. Instead, theories remain standing until they are disproven, at which point they are thrown out altogether or modified slightly.

Theories start out with empirical observations such as “sometimes water turns into ice.” At some point, there is a need or curiosity to find out why this is, which leads to a theoretical/scientific phase. In scientific theories, this then leads to research, in combination with auxiliary and other hypotheses (see scientific method), which may then eventually lead to a theory. Some scientific theories (such as the theory of gravity) are so widely accepted that they are often seen as laws. This, however, rests on a mistaken assumption of what theories and laws are. Theories and laws are not rungs in a ladder of truth, but different sets of data. A law is a general statement based on observations.

Some examples of theories that have been disproved are Lamarckism and the geocentric universe theory. Sufficient evidence has been described to declare these theories false, as they have no evidence supporting them and better explanations have taken their place.

 

[GrimJack]

Nope, radar guns are absolute - no negatives. At least the ones I got to play with.

 

[gixxer750]

car mounted radar guns are set to the vehicle speed. If the cop car is doing 30mph, he can put in that speed. The radar gun will then tell actual speed of the car that he is pointing the radar gun at.


The sun appears to be moving throughout the day.... but its not(at least not the way it appears to be), the earth is moving around it. In your perspective however, the sun is moving and the earth is standing still(from what you observe by sight only.)

 

[americanjebus]

its fun to see what goes on in your guys' brains like this.

 

[SupraMario]

actually it is FACT that the universe is expanding, the theory is whether or not it will contract back.

but that isnt really a fact, but a theory someone came up with by using math, we truely dont know this.

 

[Mr.SelfDestruct]

just reading this gave me a headache, and I wasnt even TRYING to understand it.

 

[Shawndude]

car mounted radar guns are set to the vehicle speed. If the cop car is doing 30mph, he can put in that speed. The radar gun will then tell actual speed of the car that he is pointing the radar gun at.

But does it go into negatives? What if the police officer inputs 60mph (or it figures it out automatically), and then points the gun at a car going 20 mph. What does the display spit out? Will the display show -40mph, or +80 mph, or what?

What about hand held units? Can you clock a car coming at you and going away from you? Can you tell from the display alone which way the car being clocked is going?

 

[americanjebus]

umm ya know there are more than 1 type of radar gun, im sure theres one for every situation, but the one that caught me doign 86 "the stryker2#### or other is a self calibrating device with 30mph and 60mph check points. the system is calibrated at the beginning of every shift via the auto calibrate button." only does positve values. they get as complex as modern technology can get it.

but to answer your question better they spit out the average velocity of whatever is in the line of sight in a positve value, doesnt give direction.

 

[lanky189]

but that isnt really a fact, but a theory someone came up with by using math, we truely dont know this.

they measured the distances, then measured again a long time after.... the first was shorter than the second....how is that not fact?