Moved here from another thread...

"You can have an applied force with the object in a stationary position"

Existence of a force is independent of acceleration...

You can not have a net external force without acceleration. If it is not accelerating the net force must be zero. F=ma

Likewise, a force causes an acceleration and certainly not vice versa.

For EVERY action there is an EQUAL AND OPPOSITE reaction.

Not sometimes, all the time.

Example 1:

If you push on an object and accelerate it, it pushes back with an equal and opposite reaction.

Not sometimes, all the time.

If you read the rest of Newtons Laws, you will see that it states "when acted on by an external force." The "inside" force that presses back is caused by the acceleration, and can also be found by: F=ma. Amazingly, exactly equal to the force that is accelerating it. Newton's Third Law is true after all. Who would have known?

Example 2.

If an object is subject to the Earths gravitation field, it is being accelerated (remember? 9.8m/s). If it is also not moving because it is on the surface, it applies a force on the surface equal to its weight. The force is a result of the acceleration of gravity. Acceleration causes force.

Not sometimes, all the time.


Learn first, use words like "certainly" later!

Although I have lots of patience for many things, this is not one of them.


I'm out...

 

Sorry DonQ if you didn't like my use of words, maybe it was too strong, I apologize.

But from what I've learn, fundamentally, a force produces an acceleration. Even 9.8m/ss is "due to gravity" that is, gravitational force. I can't imagine an acceleration causing a force, that is, I think all accelerations are due to an original source of force. I don't know acceleration first, then force. Also note that you can't see force with your eyes, but you can notice an object moving faster or at constant velocity or speed. Please be more patient, it's there to learn. Even if something is wrong, personally, I retain better from my own mistakes.

Thank you.

 

Nano, you draw your conclusions using your comon sense by the looks of it. And based on that it does seem to make sense at first that force causes acceleration and not the other way around.
However the math describing the proplem says otherwise. And as you know you can't beat math in regards to conlusions once proven . The math says acceleration causes force, in other words our model of modern physics states that acceleration causes force. So unless you can find a new one i'm afraid you are gonna have to aknowledge the mathematical conclusion

 

Thank you Steinar for your advice.

But I would like you to note that a Law of Physics such as that of Newton was first observed before the maths to prove it was formulated. The physical world existed before the concept of numbers was introduce. The maths amazingly helps understand the relationship between the different factors but does not explain their "nature". Maths is not Physics.
Newton first received an apple on the head, not equations. And that apple fell due to the gravitational force of the earth with an acceleration due to gravity g that caused its velocity to change from zero to something greater until impact.

Cheers.

 

For those who are interested this discussion is also being conducted in this thread

http://forum.allaboutcircuits.com/showthread.php?t=23354

 

Math is not physics? Perhaps, but physics absolutely uses math. Physics without math is not physics, and the physics and math in these subjects are very well defined indeed. You are confusing potiential energy with released energy when you talk about the apple. Step outside the math framework and you might was well believe in perpetual motion.

Personally I have hopes that quantium physics might offer a reactionless drive, but so far Neuton rules remain pretty much intact. Einstien defined some special circumstances where space time is bent, but even then Neuton is a valid simplification outside of these cases.

 

I agree that Physics definitely needs maths, but not all mathematical theories obey physical laws or even related to them. Maths goes beyond Physics. As for the apple, in a very simple way, it initially has potential energy which is converted into kinetic energy as it falls. I cannot see where is the confusion and I would be grateful to know.

Thank you.

 

Potential energy isn't energy. It become energy, but it is not.

You can not seperate math and physics. Math is the language of physics. There are maths that don't relate to physics, but the reverse is not or never will be true.

 

A living example of energy,before birth that flat reference line-o,then
out come a baby.A slap on the butte you get sound modulation,energy
that will rise above the flat line. Before birth that baby can have life
saving heart surgery. So you have energy before you have energy in
some terms,how does this apply to your physics. It has energy and energy.
But by instrument thinking you have flat line reference from 0-to postive.

 

I don't see what babies have to do with anything, but here goes anyway. Before birth the mother is supplying energy to the baby. Although we don't see the outcome of this, the energy goes towards increasing the mass of the baby, and occasionally the mother will feel the baby kicking or moving around- again, energy being used. As soon as the baby is born, you get new types of energy- sound (lots of sound!), more movement, growth (still) which also takes energy. So less energy is "spent" on growth, more on sound and movement after it's been born.

If no energy is put into the baby prior to it being born, you don't get a baby out.



As for acceleration causing force, and force causing acceleration, they're inexorably linked. F=MA, or if you prefer, A=F/M. It's more convenient from a maths POV to look at it as F=MA because multiplication is easier than division, but at the end of the day it doesn't matter and it doesn't make a difference!

 

JUst helping you about energy and when energy starts,a living example. You measure it with new and fuzzy math. A=female/male =energy.It does matter,you are with us to debate energy. Have a good day.

 

Energy=(female/male)*n

where

(female/male)=sex

n=times per night

 

n=times per night

mik3, i've always been impressed with your technical knowledge. However, if you need a running index (n) to keep track of that ..... now I'm really impressed!

 

Potential energy isn't energy. It become energy, but it is not.

Wow! First time I'm hearing that potential energy is not energy. How would you call it then, gravitational energy is a "potential" of energy maybe? Is the term "potential energy" ambiguous? (when I don't know, I ask questions). As for the acceleration causing a force, I'm not yet convinced, until someone come up with something to convince me.

You can not seperate math and physics. Math is the language of physics. There are maths that don't relate to physics, but the reverse is not or never will be true.

I completely agree on that, I never meant the opposite in saying maths is not physics. What I meant was you can have maths calculation resulting in, for instance, infinity which won't always be true in physics, and sometimes physics might classify such cases as "ideality".

Cheers.

 

mik3, i've always been impressed with your technical knowledge. However, if you need a running index (n) to keep track of that ..... now I'm really impressed!

LOL

Usually n is greater than 1.

 

LOL

Usually n is greater than 1.

Some find it easier to tally with "n!"

As for the acceleration causing a force, I'm not yet convinced, until someone come up with something to convince me.

It all depends where you look at it from. From the sidelines, looking at the block, there is a force applied to the block which then moves (accelerates), assuming friction isn't ridiculous.

If you look at it from a different perspective:

You're sitting in a car. The car accelerates, and because of this exerts a force on the ground to move.

They're linked. Just as x=y, y=x. Force is proportional to acceleration, acceleration is proportional to force.

 

Some find it easier to tally with "n!"

Do you mean n factorial?

 

It all depends where you look at it from. From the sidelines, looking at the block, there is a force applied to the block which then moves (accelerates), assuming friction isn't ridiculous.

If you look at it from a different perspective:

You're sitting in a car. The car accelerates, and because of this exerts a force on the ground to move.

They're linked. Just as x=y, y=x. Force is proportional to acceleration, acceleration is proportional to force.

I understand your point, but still, that car acceleration is due to the torque of the wheels, which is force again. It's action and reaction, but again, I see force the "cause", not acceleration. I see acceleration the "product", not the "origin" of force. I'm still waiting for something more convincing. F=ma, force is related to acceleration, they might both be "appearing" simultaneously. But I don't know any case where acceleration comes first. I know force present and no motion. But acceleration without force, isn't clear. The only case I know where you have acceleration with constant speed is rotation, there the acceleration is towards the centre of rotation. And that's a case where there is a change in direction. Acceleration (and velocity) is a vector quantity whereas speed is scalar.

Thank you.

 

I'm engineer and I think most of us here are. Are there any physicists on this forum to answer to my query please?

 

Wow! First time I'm hearing that potential energy is not energy. How would you call it then, gravitational energy is a "potential" of energy maybe? Is the term "potential energy" ambiguous? (when I don't know, I ask questions). As for the acceleration causing a force, I'm not yet convinced, until someone come up with something to convince me.



I completely agree on that, I never meant the opposite in saying maths is not physics. What I meant was you can have maths calculation resulting in, for instance, infinity which won't always be true in physics, and sometimes physics might classify such cases as "ideality".

Cheers.

Ok, so you boost something out of the earth's gravitational field, where it will never return. Is that potential energy? A potential is just that, something that could be, but isn't.