If it doesn't agree with experiment, it's wrong. Part II

[Crazy Chainsaw]

This is correct, because the definition of deceleration is:

We can also say that if something is slowing down its velocity is decreasing. If velocity is decreasing with respect to time it is decelerating.



"Might" is not the correct word. The acceleration will be reduced. Newton's third law of motion says it has to be reduced.

At the instant of collision, the velocity will change. It has to. If an object is moving in one direction, and it encounters a force in the opposite direction of its motion - even for an instant, it's velocity will change. In fact, its velocity will be less than it was before the impact, if the force is in the opposite direction. Newton's third law of motion says this has to be true.

The definition of acceleration is change in velocity with respect to time. If the velocity changes, even for an instant, then the acceleration must also change, even if it's just for an instant.

The collision does alter the acceleration. The collision provides a force in the opposite direction of travel. A force in the opposite direction of travel will reduce the velocity of the falling object, even if it's just for an instant. If the velocity of an object is reduced with respect to time, then the object is said to decelerate.



This is wrong.

Let me break this down concept by concept.

1. If an object is in motion it has a velocity. Velocity is the speed of the motion and direction of motion.
2. Acceleration is a change in velocity with respect to time.
3. If the velocity is increasing with respect to time it is said to accelerate.
4. If the velocity is decreasing with respect to time it is said to decelerate.

Let me summarize this.

If velocity increases with respect to time there is acceleration.
If the velocity stays constant with respect to time there is no acceleration.
If the velocity decreases with respect to time there is deceleration.

Are any of the above statements incorrect? No.

Now, let's break down your statement to show why it's wrong.

. This is wrong because in your example an object is accelerating downwards. To be perfectly clear, this means that the velocity is increasing in the downwards direction with respect to time. In your example the accelerating object then collides with another object.

This is wrong. Newton's third law says that for every action there is an equal and opposite reaction. If your example object is accelerating downwards, at the instant of impact with the other object the velocity will change. It has to, because it is encountering a force in the opposite direction of travel. The opposite force causes the velocity to decrease. What term do we use when the velocity of an object decreases with respect to time? The term is deceleration.

If there is deceleration, and Newton has have proven there is, your statement is wrong.



The above statement is correct.



No, I don't. I just corrected you. If you want to be taken seriously, admit you were wrong and move on.

Gravity is the downward force gaining momentum, 2600lbs dropped 12/feet, =100000lbs,

Electromagnetism is the force resisting Collapse, the forces of Gravitational momentum vs resistance are Unequal, and mass adds to gravitational momentum.

At higher scales Gravity will have a higher magnitude than Electromagnetic bonding,
At lower Scales Electromagnetic bonding will have a higher Magnitude than Gravity.

That is your misconception.

 

[FalseFlag]

Congratulations. Let's extend the thought experiments: I predict that if I gently place a brick on a piece of tissue paper and it can't hold the brick's weight, then if I drop the brick on the tissue paper, it will not cause the brick to decelerate; it will only cause a brief decrease in the acceleration due to gravity.

Your prediction is not right. There will be an instantaneous deceleration at the instant of impact. There has to be.

I just explained this in post #317.

 

[Crazy Chainsaw]

Your prediction is not right. There will be an instantaneous deceleration at the instant of impact. There has to be.

I just explained this in post #317.

No only if the upward electromagnetic forces are of significant magnitude to cause a deceleration that is noticeable.

It also will not be one force but multiple forces, acting independently.

 

[PhantomWolf]

Oh, no. It's YOUR misunderstanding. It isn't as common as you might think.

Actually I suspect that it is. People intuitively conflict the force that the weight of an object applies to the ground, with the force of gravity pulling the object down. I'd say that it's pretty common for lay people to get it wrong. Even looking through pages and video on the net, the terminology for these things often isn't the dame from page to page which can cause more confusion.

 

[FalseFlag]

This is only true if the net force on the object is opposed to the direction of travel. In the brick-through-tissue example, for instance, that does not happen because the small force imparted by the tissue is (much) smaller in magnitude than the weight of the brick (i.e., the gravitational force on the brick). In that case, the velocity of the brick is never reduced; in fact, it continues to accelerate (speed up) during the impact, just not as much before and after.

Wrong. Equal and opposite have nothing to do with one object breaking another. Those are separate concepts.

I do understand your statement, but it's wrong.

You assume that because gravity always causes the brick to accelerate downwards at g, the force exerted by the brick is not enough to change the acceleration.

I have gone to great lengths to accurately explain the concepts involved in post #317.

I can briefly summarize your error as follows:

The velocity of a falling brick increases over time. This is because of the acceleration due to gravity.

At a given instant, the brick impacts a piece of rice paper. Newton's third law tells us what must happen. At the instant of impact, the brick will exert a force on the rice paper. The rice paper will exert an equal force on the brick in the opposite direction. This force, in the opposite direction of travel, must change the velocity of the brick. It has to. If the velocity changes for an instant, then acceleration must change. If the velocity has decreased with respect to time, the brick has experienced a deceleration.

After the instant of impact, the rice paper is no longer in the path of travel. The velocity of the brick will then start to increase again.

Your argument is the paper has to exert a large enough force to cause a noticeable change in the velocity of the brick. This is not true. Just because the magnitude of change in velocity is not great enough to see with the naked eye that does not mean it's not there.

Also, because someone is going to mention gravity in regards to the action-reaction pair issue, let me address that. When you consider the action-reaction pair of the earth's gravitational force on the brick, and the brick's gravitational pull on the earth, those forces are balanced. They have to be because the brick is accelerating downwards at g. Those balanced forces have no effect whatsoever on the brick as it impacts the paper, when trying to explain the basic concepts involved. And, since I know skeptics want to take things to extreme levels just to complicate things, the same thing applies to the paper. The gravitational forces are balanced. If the paper is being supported by something, then the normal forces are balanced. Stop making things needlessly complex. When you do that it prevents you from easily understanding easy concepts.

 

[Dave Rogers]

At the instant of collision, the velocity will change. It has to. If an object is moving in one direction, and it encounters a force in the opposite direction of its motion - even for an instant, it's velocity will change. In fact, its velocity will be less than it was before the impact, if the force is in the opposite direction. Newton's third law of motion says this has to be true.

This is incorrect. Consider an object of mass m falling under gravity in a vacuum, which is therefore accelerating at 1g. It strikes an obstacle which, at the instant of collision, exerts a force of mg directly upwards. What is the acceleration of the object at that instant? Will the object's velocity be increasing or decreasing at that instant?

Now, consider the same falling mass striking an obstacle that at the moment of collision exerts a force of mg/2 directly upwards. What now is the acceleration of the object at that instant? Will the object's velocity be increasing or decreasing at that instant?

In both of these examples, the force opposes the direction of motion, but the velocity does not decrease. Try to understand why not.

A force in the opposite direction of travel will reduce the velocity of the falling object, even if it's just for an instant.

Wrong. A force in the opposite direction greater than the sum of the forces the object is already subject to will reduce the velocity of the falling object. A lesser force will reduce its acceleration, but not its velocity. And deceleration is defined not as a decrease in acceleration, but in velocity.

And that is the most important application of Newton's Laws to the collapses in this context, and one that you need to understand.

Dave

 

[PhantomWolf]

His own video proves your right hilarious another self debunking.

Give him a bit of credit, he is learning, just slowly. he's admitted he was wrong about the force pairs, and that is a start. A few more Parts to the Thread and he might be ready for Physics 101.

 

[Dave Rogers]

Give him a bit of credit, he is learning, just slowly. he's admitted he was wrong about the force pairs, and that is a start. A few more Parts to the Thread and he might be ready for Physics 101.

I think our next step is to try to teach him adding and subtracting. Is that going too fast?

Dave

 

[FalseFlag]

I'm not sure whether poor old FF hasn't grasped the semantics of the difference between "reduced rate of acceleration" and "deceleration" or whether he hasn't grasped the actual difference. Whichever, as it has been explained a hundred times, would be a major embarrassment to anyone else.

Have you grasped this? If you have, show us.

 

[FalseFlag]

I think our next step is to try to teach him adding and subtracting. Is that going too fast?

Dave

Please explain why my addition and subtraction skills are lacking.

 

[sts60]

Your prediction is not right. There will be an instantaneous deceleration at the instant of impact. There has to be.

No, there cannot be. From the statement of the problem, the tissue is unable to exert a force equal in magnitude to the weight of the brick, which is the force exerted by gravity on the brick.

If you place it gently on the tissue, and let go, the brick starts at zero speed and immediately accelerates downward.

If the brick is already falling, it is accelerating at g (neglecting air resistance) before it hits the tissue. At the "instant" of impact, it is stil accelerating, at (g - the small upward force exerted by the tissue). After the impact, it is accelerating at g again. At no point is the brick ever decelerating (slowing down); it's downward speed never stops increasing.

I just explained this in post #317.

In that post you had a little wiggle room, because one could argue for a resistive force greater than the weight of the object. You have no such situation here, by the explicit statement of the problem.

As you said,

If you want to be taken seriously, admit you were wrong and move on.

This is what you need to do.

 

[Dave Rogers]

Please explain why my addition and subtraction skills are lacking.

OK. If an object of mass m is experiencing a downward force of mg due to gravity, and an upward force of mg/2 due to a collision with an obstruction, what is the direction of its overall acceleration?

If you think the answer is "upwards," which you have repeatedly stated to be the case, then your addition and subtraction skills are lacking as applied to forces, possibly because you fail to understand they are even applicable to forces.

Dave

 

[Belz...]

No.

Your post shows that you have a gross concept error. Newton's third law of motion says that for every action there is an equal and opposite reaction.

Your example proves you do not understand this.

No. YOU prove that you don't understand what the third law is or where it applies. You think it's a universal concept that applies to everything no matter what. That is YOUR ignorance, not mine or anyone else's.

 

[Belz...]

Please explain why my addition and subtraction skills are lacking.

Oh, so you don't understand figures of speech, either?

 

[PhantomWolf]

You seem to be making the same mistake again. Newton's First Law says that if they accelerate (or decelerate), it's because the forces are not in equilibrium, therefore they are not equal and opposite. This should be bleeding obvious. There's a limit to how much opposing force the connections can exert to oppose the movement of the falling floor. Past that, you get acceleration (=imbalanced forces). That's a case where the magnitude of N+ and N- does not equal that of G+ and G- (using PhantomWolf's terminology).

Okay this isn't quite right. All forces between two objects have a force pair that are equal and opposite. This means that when a weight falls on the floor, the floor will respond with an equal and opposite force. Now if that floor has a limit to the amount of force it can respond to before it deforms or breaks, or the wall connections fail, and the falling weight exceeds that force, then that will still be the maximum force that can be applied to it, and the total force that it will apply back on the object that has fallen on it. Once it fails, the weight will continue to apply excess force to it, and it will continue to apply an equal force until they are moving at the same velocity.

Note that these force pairs act on different objects.

Acceleration occurs when an object has a unbalanced force action on it, not when the force pairs are unbalanced.

For example if we placed a book on the floor, the book would have gravity pulling it down, and the floor pushing it up. These would be equal and opposite meaning that they cancel out and the book remains stationary, but they aren't a force pair. Now if we disintegrate the floor leaving the book with nothing to rest on, it will still have gravity pulling it down. The equal force pair is still there, with the book attracting the Earth upwards, but since there is only a single force acting on the book now, it will accelerate downwards.

You are actually making the exact same mistake that FF made, getting Force Pairs mixed up with combined forces acting on a single body.

 

[FalseFlag]

Consider an object of mass m falling under gravity in a vacuum, which is therefore accelerating at 1g. It strikes an obstacle which, at the instant of collision, exerts a force of mg directly upwards. What is the acceleration of the object at that instant? Will the object's velocity be increasing or decreasing at that instant?

If you're trying to make a point, why don't you just make it?

 

[WilliamSeger]

the reaction force of a floor when another floor falls on it is not necessarily equal to the force the other floor exerts on it.

No.

Your statement is proof that you don't understand Newton's third law of motion. You are a victim of the tricks that the "experts" have done. They have intentionally over-complicated things so that it is easier to get concepts confused.

Pgimento's statement is not quite correct, but you've misidentified the reason. A correct statement would be "the reaction force of a floor when another floor falls on it is not necessarily equal to the force the other floor is capable of exerting on it. By the 3rd Law, yes, we know that the downward force and the reaction force are always equal and opposite, but when the reaction force reaches its maximum limit and the floor fails, the actual force acting on it reaches that exact same limit at the same time, regardless of how much potential force is available due to gravity and inertia. So: the maximum reaction force is the controlling limit for both forces; the reaction force is the only force acting to slow the falling mass; and the difference between the maximum reaction force and the potential force is what determines whether or not the floor fails.

(ETA: Once again, I type too slow. )

 

[FalseFlag]

OK. If an object of mass m is experiencing a downward force of mg due to gravity, and an upward force of mg/2 due to a collision with an obstruction, what is the direction of its overall acceleration?

If you think the answer is "upwards," which you have repeatedly stated to be the case, then your addition and subtraction skills are lacking as applied to forces, possibly because you fail to understand they are even applicable to forces.

Dave

If you're trying to make a point then you should make it. If you claim I'm wrong, please show me why I am wrong.

 

[Dave Rogers]

If you're trying to make a point, why don't you just make it?

My point is that you don't know the answer to those questions, when you try to work it out you get it wrong, and when anyone points out that you got it wrong you insist you're right because you know better than everyone else. You've found out you were wrong about gravity; try to consider the possibility that you're equally wrong about adding and subtracting forces.

Dave

 

[FalseFlag]

To be fair I don't recall Criteria lecturing others on physics; that's FalseFlag's speciality. I see Criteria asking to improve his understanding.

You could follow Criteria's example.