Ask a physicist anything. (8)

[AV1611VET]

If a car weighs 1000 pounds, will it take 1001 pounds of force to set it in motion (on a flat surface)?

 

[essentialsaltes]

If a car weighs 1000 pounds, will it take 1001 pounds of force to set it in motion (on a flat surface)?

No, it would take 1000 pounds of force to lift the car, fighting directly against the force of gravity (i.e. weight). Making it roll would generally require much less force, as you overcome various frictional forces.

If you've ever pushed a car in neutral, you shouldn't flatter yourself that you've been exerting forces of a ton or more.

 

[DennisTate]

I'm a Single White (mixed actually) Christian male, 43 years old. And I want to be an astronaut.

Watch out for those G-force testing devices!

You might have an out of the body experience and go through such a transformation that your family hardly recognizes you!


James Whinnery - near-death experiences from gravity

The Trigger of Gravity

Dr. James Winnery's NDE research


The scientific method requires a phenomenon to be able to be reproducible under laboratory conditions for it to be declared a "real" phenomenon. In the early days, near-death experiences were thought by some to be just "phantom" visions and nothing more than imagination. But then Dr. James E. Whinnery, a chemistry professor with West Texas A&M, became involved with research involving fighter pilots being subjected to extreme gravitational forces in a giant centrifuge to simulate the extreme conditions that can occur during aerial combat maneuvering. Strangely enough, it turns out that under extreme g-forces, fighter pilots lose consciousness and have a near-death experience. Whinnery wrote a technical report for the National Institute for Discovery Science about the phenomenon and in doing so proved the near-death experience to be a real phenomenon. The following is a summary of his technical report of how NDEs are triggered by severe gravitational forces.

 

[AV1611VET]

No, it would take 1000 pounds of force to lift the car, fighting directly against the force of gravity (i.e. weight). Making it roll would generally require much less force, as you overcome various frictional forces.

If you've ever pushed a car in neutral, you shouldn't flatter yourself that you've been exerting forces of a ton or more.

Okay, thank you!

 

[Jonathan Jarvis]

Here is a question that has taxed me in my idle moments.

Is time linear? If it is, has it always been so. If it follows a curve what is the formula for that curve. For either what are the constants and variables.

The assumption I am basing this question on is that matter and time started with the "big bang".

 

[Cactus Jack]

Hydrogen, nitrogen and oxygen are gases. All three are "invisible" to the naked eye.
If you mix the lightest of the two, hydrogen & oxygen, you get water which is, of course, visible and liquid.
But if you mix hydrogen, oxygen and nitrogen, you get "air". Which is (in it's clean state) invisible. Even though nitrogen is heavier than hydrogen and oxygen.

Please explain.

 

[essentialsaltes]

Hydrogen, nitrogen and oxygen are gases. All three are "invisible" to the naked eye.
If you mix the lightest of the two, hydrogen & oxygen, you get water which is, of course, visible and liquid.
But if you mix hydrogen, oxygen and nitrogen, you get "air". Which is (in it's clean state) invisible. Even though nitrogen is heavier than hydrogen and oxygen.

Please explain.

There is a difference between a mixture and a compound. In a mixture, no chemical reactions take place between the elements.

Air is a mixture of hydrogen gas, oxygen gas, and nitrogen gas. As such, it behaves very much like you'd expect a mixture of these things. Air is a transparent gas.

Water is a chemical compound of hydrogen and oxygen. To make water out of hydrogen and oxygen, you can't merely mix them together, you have to ignite it, so that a chemical reaction occurs in which bonding between oxygen and hydrogen atoms occurs. This molecular compound (water) can have very different properties than the individual elements.

 

[AV1611VET]

In a mixture, no chemical reactions take place between the elements.

Interesting -- is that why water and oil don't mix?

 

[mandyangel]

Interesting -- is that why water and oil don't mix?

Hey AV!!! Love, Mandy

 

[AV1611VET]

Hey AV!!! Love, Mandy

Hi there, Mandy!

Long time, no see!

 

[mandyangel]

Nice to see you!

 

[essentialsaltes]

Interesting -- is that why water and oil don't mix?

Not exactly. When you make your salad dressing, you are certainly making a mixture, not a compound. And yes, it's difficult to make a homogeneous mixture of oil and water.

But the reason for that has to do with the nature of the molecules. Water is a polar molecule (meaning that its electrical charges are not evenly distributed), while oils are non-polar molecules. If I'm remembering the chemistry right, polar molecules are typically easy to dissolve in polar molecules, and the same with non-polar/non-polar, but one of each don't mix readily.

 

[essentialsaltes]

staff edit

Which is better? Better for what? Well, I understand the stimulating effect of cold on the aureolae will probably have a stimulating effect on the audience as well. But better for you is probably the temperature that's most comfortable.

 

[essentialsaltes]

Here is a question that has taxed me in my idle moments.

Is time linear? If it is, has it always been so. If it follows a curve what is the formula for that curve. For either what are the constants and variables.

The assumption I am basing this question on is that matter and time started with the "big bang".

It depends what you mean by linear.

As far as we know, time has only one dimension. Space has three: up/down, fron/back, left/right. But time only seems to have past and future. In that sense time is like a line.

Einstein's theories of relativity show that different observers may measure time differently. Two identical clocks, one that is moving and one that is not, will run at different speeds. Two identical clocks, one that is in a gravity well (say on the surface of the earth) and one that is far in outer space, will run at different speeds. So in this sense time is not the same for all situations.

More philosophically, one might ask whether the rate at which time passes changes. It's hard to say if this even has any meaning. We tell how fast something is going in distance by measuring how many miles go by in an hour. You can go 20 miles per hour or 40 miles per hour. But if you try to measure how fast time is going, you have to ask how many hours go by in an hour? Exactly 1. If some omnipotent being made our time run faster or slower (compared to his super-duper outside the universe clock) we would never know it. If our pulse slowed down, we could never measure it, because our watch would also have slowed down the same amount.

 

[essentialsaltes]

but if u had to guess as a physist what would you say?

I really don't know. You'd have to ask an astronomer. They know more about heavenly bodies.

 

[Naraoia]

But the reason for that has to do with the nature of the molecules. Water is a polar molecule (meaning that its electrical charges are not evenly distributed), while oils are non-polar molecules. If I'm remembering the chemistry right, polar molecules are typically easy to dissolve in polar molecules, and the same with non-polar/non-polar, but one of each don't mix readily.

That got me wondering. Is the difficulty of mixing polar and non-polar things due to repulsion, or is it merely differential attraction? If you could put one oil molecule and one water molecule next to each other, would they stick, or would they still run away from each other?

 

[essentialsaltes]

That got me wondering. Is the difficulty of mixing polar and non-polar things due to repulsion, or is it merely differential attraction? If you could put one oil molecule and one water molecule next to each other, would they stick, or would they still run away from each other?

I guess, given those two choices, it would be closer to differential attraction. Molecules are (over all) electrically neutral, so there's no net repulsive force. But the polar molecules have electric dipoles that interact, sorta like magnets. So they tend to stick together, and the boring old nonpolar molecules aren't as interesting to them.

Taking two isolated molecules, I'm guessing you'd get a weak attractive force, like the van der Waals force, with the polar molecule inducing a slight dipole in the nonpolar molecule, making them attract. But this is not as strong as a dipole-dipole interaction between two polar molecules.

 

[Wiccan_Child]

but if u had to guess as a physist what would you say? i'm all for the experiments though. thats some science even I am down for lol.

20°C should suffice. Any colder and it might be uncomfortable, any hotter and it might become painful.

 

[Jonathan Jarvis]

It depends what you mean by linear.

As far as we know, time has only one dimension. Space has three: up/down, fron/back, left/right. But time only seems to have past and future. In that sense time is like a line.

Einstein's theories of relativity show that different observers may measure time differently. Two identical clocks, one that is moving and one that is not, will run at different speeds. Two identical clocks, one that is in a gravity well (say on the surface of the earth) and one that is far in outer space, will run at different speeds. So in this sense time is not the same for all situations.

More philosophically, one might ask whether the rate at which time passes changes. It's hard to say if this even has any meaning. We tell how fast something is going in distance by measuring how many miles go by in an hour. You can go 20 miles per hour or 40 miles per hour. But if you try to measure how fast time is going, you have to ask how many hours go by in an hour? Exactly 1. If some omnipotent being made our time run faster or slower (compared to his super-duper outside the universe clock) we would never know it. If our pulse slowed down, we could never measure it, because our watch would also have slowed down the same amount.

That was the conundrum. If matter (3 dimensions) exists in time (the fourth) then there should be some way of measuring it in relation to the other three.

The only basis of measurement we can experience in respect to rate of change is time.

I read somewhere that physicists have posited there are more dimensions than the four that we experience. I thought article said it was about 17.

Maybe time can be measured against gravity.

 

[FreeinChrist]

MOD HAT

Sorry - had to do a bit of clean up. There was some inappropriate discussion going on .