Thread: friction and speed

1. hello all, my first post so go easy on me :wink:

ive read various other threads on this forum, and understood absolutely nothing. compared to the questions they pose, my question is very simple. i would like to know why friction increases as speed increases, and why this is in terms of particles.

i dont particularly like physics, i prefer biology and stuff to do with the human body.

thanks

2.

3. Okay, I will do my best to explain it as simple as possible.

Friction increases with speed because the faster you go, the more the molecules are striking your surface per second.

In something which moves through a fluid or a gas, it is this friction which creates something called "drag"

Also...the faster you go, the faster the velocity of molecules that are hitting you....As soon as the molecule hits you it is stopped or slowed down so it will loose some of its movement or "kinetic" energy.

Because energy cannot be destroyed; ONLY converted, this kinetic energy is transferred in the form of thermal or HEAT energy.

4. thanks, that was really helpful.
do you know any sites which go into more detail yet are easy to understand? i tried googling it but nothing useful comes up.

5. I have found an article on wikipedia that may help you. It does go into more detail but it is a bit more complicated.

What I would suggest is that you read it bit-by-bit and try to visualise in your mind what the article is saying happens and then once you have got that in your mind and can understand it, then go on to the next bit.

There are a few equations on there too.

The link:

http://en.wikipedia.org/wiki/Friction

Try thise too (its VERY basic):

http://www.fearofphysics.com/Friction/frintro.html

You could also try googling the word "Tribology" (Tribology is the study of friction)

Hope this helps :-)

6. ok, thanks again for that.

if i want to estimate a size of a force, how exactly can i do this? is there a unit for measuring friction? N?

i just want to find out approximately how much force is driving an airplane forward and how much pushing it back when the airplane is accelerating. this would allow me to draw a fully labeled force diagram of a airplane:
still
accelerating
steady speed
slowing down and landing
which is what i wnat to ultimately do. but i dont understand how i can label this diagram with all the names of the forces (friction etc) plus estimate the size of the forces with units. of course, the sizes dont have to be precise, just approximations.

7. Okay,

This is a little beyond my knowledge. Truly.

What I CAN tell you is that you would need to take into account the forward movement of the aeroplane (thrust) Then you would need to take into account the RELATIVE airspeed of the airplane. You would also need to take things into account such as air density and temperature. The surface areas of the airplane should be taken into account too, not just in size, but also in construction materials, along with the shape of the wings and fuselage. There are SO many things to be factored in when calculating something like this. The friction that you are talking about by the way induces something called "drag" Im not too sure what the measurment is called though.

On an aircraft in flight, there are four forces acting upon it. they are: 1) Lift (pushing the aircraft up) 2) Gravity (pulling the aircraft down) 3) Thrust (pushing the aircraft forwards) and 3) Drag (slowing the aircraft down through friction)

If anyone else on here can explain it a little more then that would be great.

8. wow, sounds complicated.

i think ill just draw a force diagram with simple arrows, the arrows dependent on the size of the force.

and thrust was just the word i was looking for, i didnt know how to describe the airplanes forward movement, thanks.

and when we stand stil on earth, we experience gravity and ??? what keeps us up? what is it called?

thakns

9. Im not too sure what you mean.

If we stand still on the earth; we experience gavity. Are you asking what forces keep an airplane up ? If you are; then the force is called: "Lift"

10. Originally Posted by young_scientist
wow, sounds complicated.

i think ill just draw a force diagram with simple arrows, the arrows dependent on the size of the force.

and thrust was just the word i was looking for, i didnt know how to describe the airplanes forward movement, thanks.

and when we stand stil on earth, we experience gravity and ??? what keeps us up? what is it called?

thakns
It's called, muscles and a sense of balance - If you relax or lose either you fall down.

11. muscle tension is a bit more correct.
btw since you're interested in the human body, it might be interesting for you to know that muscles can only contract and relax.

an airplanes lift is dependant on airspeed.
the air bends around the top of the wing, and is pushed downwards at the rear. its like you have a thrust generated at the rear edge of the wing,
and the thrust increases as the airspeed increase.

oh and btw, forget everything you've read about pressure above and below the wing. that stuff is just confusing, and not really physically accurate anyways.

drag is usually dependant on the profile towards the direction of travel.
if the profile is large, the drag is high.
thats the basics.

12. Originally Posted by dejawolf
muscle tension is a bit more correct.
btw since you're interested in the human body, it might be interesting for you to know that muscles can only contract and relax.
As well as grow, shrink, decay...

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