So I get the problem when you have the mass of the object and the velocity of the object. I just don't understand it when you have just kg*m/s

I don't know what you are trying to get (if it is momentum, then just do kg*m/s) Yes, kg*m/s is enough to solve for momentum Kg is the unit for mass M/S is the unit for velocity

so if I get this right, Momentum and force are correlated? since by my understanding saying 40 Netowns is the same as saying 40 kg * m/s^2 momentum. fun fact: a force of 40Newtons is around 4KG of weight force. 1 meter / second is 3.60km/h

Force would be the rate of change of momentum.

how is 40 N equivalent to 40kg * m/s2

I just posted this in the comment section that follows, so well, I hope u can understand why kg m/s^2 is the unit for force. Well, we humans are too lazy to write the whole thing, that is, 'kg m/s^2' every time we talk about force and its units. So, we decided to keep another unit, N, that is , Newton. Consider this, when we are given a math problem of this type , " **insert name** has 5 apples which amount to 25 (unit currency). Now, the person wishes to buy 3 more apples from the same shop. Calculate the extra money he needs to pay." We simply divide 25 by 5 to get the cost of one apple, and then multiply it by three. Well, this is not so lengthy at this stage for most of us, but it does cause quite some silly calc errors. It would have been way easier if we just had the cost of one apple from the beginning, right? Similarly, in force, what we do is this: We consider a case where an acceleration of 1 m/s^2 is produced for a mass of 1 kg when a certain force is applied. And, according to the formula, we get the answer as 1 kg m/s^2 . This 1 kg m/s^2 is given the name Newton and the symbol 'N'. Thus, in your case, when we say 40N, we say _40 x 1 N_ that is _40 x 1 kg m/s^2_ . This is why they're equal. Hope this helps, and sorry for such a lengthy explanation. I seem incapable of explaining in short.

Im having trouble understanding conservation of momentum, I understand the other lessons well but not this one. Ive watched and read the articles and videos, can someone explain in simpler terms.

Momentum is not gained or lost. The initial or first momentum should equal the last momentum. This is only if there are no external forces applied

Main content

Course: High school physics - NGSS > Unit 1

Lesson 3: Conservation of momentum

Conservation of momentum

Google Classroom

Review your understanding of the conservation of momentum in this free article aligned to NGSS standards.

Key terms

Term	Meaning
System	The collection of objects that are of interest.
Closed system	A system in which masses do not enter or leave.
Isolated system	A system in which no net external forces act on the objects within it.
Momentum	The quantity of motion. Momentum is the product of mass and velocity, and because velocity is a vector, momentum is also a vector.
$Δ (m \vec{v})$ ‍	The change in momentum.
$Δ t$ ‍	The change in time, or the time interval.
${\vec{F}}_{net}$ ‍	The net external force.

Equations

Equation	Symbol breakdown	Meaning
$\vec{p} = m \vec{v}$ ‍	$\vec{p}$ ‍ is momentum, $m$ ‍ is mass, and $\vec{v}$ ‍ is velocity.	The momentum of an object is the mass of the object multiplied by the velocity of the object.
$Δ (m \vec{v}) = \vec{F} Δ t$ ‍	$\vec{F}$ ‍ is the external force, $Δ t$ ‍ is the time interval, and $Δ (m \vec{v})$ ‍ is the change in momentum.	The change in momentum is the product of the external force acting and the length of time that force acts.

Momentum and force in a system

Momentum of an object is the product of the object’s mass and velocity. We also know that a net force acting on the mass will result in the acceleration of that mass:

\vec{F} = m \vec{a}

A net force acting on an object can change the object's velocity, and therefore its momentum. The change in velocity due to a net force will increase the longer that force acts on an object:

\vec{F} Δ t = m \vec{a} Δ t = m Δ \vec{v} = Δ m \vec{v} .

The relationship

\vec{F} Δ t = Δ (m \vec{v})

also applies to a system, or collection of objects.

In a closed, isolated system, the net external force is

0

, so the change in momentum is also

0

. In other words, momentum is conserved for closed, isolated systems.

However, how the system is defined is important. For instance, consider two ice skaters who are at rest and facing each other, as shown above. They push off of each other and move in opposite directions. Taking both skaters together as a system, the total momentum is

0

both before and after they push off each other, because the push off is an internal force.

Taken separately as two different systems, the push off is an external force acting on both skaters, and their momenta both change. The momentum lost by one skater is taken up by the other skater.

What else should I know about conservation of momentum?

The conservation of momentum has practical consequences. The relationship between momentum and force can help us study forces using easily measured quantities. For instance, by knowing the masses and velocities of objects before and after a collision, we can learn about the forces involved during that collision.
${\vec{F}}_{net} Δ t$ ‍ is referred to as the impulse. The quantity ${\vec{F}}_{net} Δ t$ ‍ is referred to as the impulse, for which the symbol $J$ ‍ is used. The equation ${\vec{F}}_{net} Δ t = Δ m \vec{v}$ ‍ is thus often referred to as the impulse-momentum theorem in many textbooks.
Internal forces do not affect the momentum of the system. Because of Newton’s Third law, the forces acting between masses within a system cancel in pairs and do not contribute to the system’s momentum.
Momentum may be conserved in one direction but not in another. Momentum is conserved in the direction of ${\vec{F}}_{net},$ ‍ but it is not conserved in the perpendicular direction. For example, in projectile motion, the momentum changes vertically because of the force of gravity downwards. However, momentum does not change horizontally, because there are no horizontal forces.

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jasmine harvey
Posted a year ago. Direct link to jasmine harvey's post “How does one slay the day...”
How does one slay the day in regards to physics?
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- 1 Prime
  Posted 3 days ago. Direct link to 1 Prime's post “Slaying the day in physic...”
  Slaying the day in physics involves approaching the subject with enthusiasm, curiosity, and a proactive mindset. To excel in physics, you can start by understanding the fundamental concepts thoroughly, practicing problem-solving regularly, and seeking clarification whenever necessary.
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Diana
Posted 3 years ago. Direct link to Diana's post “So I get the problem when...”
So I get the problem when you have the mass of the object and the velocity of the object. I just don't understand it when you have just kg*m/s
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- zombiemanstyle
  Posted 2 years ago. Direct link to zombiemanstyle's post “I don't know what you are...”
  I don't know what you are trying to get (if it is momentum, then just do kg*m/s)
  
  Yes, kg*m/s is enough to solve for momentum
  
  Kg is the unit for mass
  M/S is the unit for velocity
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  (9 votes)
686247
Posted 3 years ago. Direct link to 686247's post “how is 40 N equivalent to...”
how is 40 N equivalent to 40kg * m/s2
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(4 votes)
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- Anonymouse14
  Posted 2 years ago. Direct link to Anonymouse14's post “I just posted this in the...”
  I just posted this in the comment section that follows, so well, I hope u can understand why kg m/s^2 is the unit for force.
  
  Well, we humans are too lazy to write the whole thing, that is, 'kg m/s^2' every time we talk about force and its units. So, we decided to keep another unit, N, that is , Newton.
  
  Consider this, when we are given a math problem of this type , " *insert name* has 5 apples which amount to 25 (unit currency). Now, the person wishes to buy 3 more apples from the same shop. Calculate the extra money he needs to pay." We simply divide 25 by 5 to get the cost of one apple, and then multiply it by three. Well, this is not so lengthy at this stage for most of us, but it does cause quite some silly calc errors. It would have been way easier if we just had the cost of one apple from the beginning, right?
  
  Similarly, in force, what we do is this:
  
  We consider a case where an acceleration of 1 m/s^2 is produced for a mass of 1 kg when a certain force is applied. And, according to the formula, we get the answer as 1 kg m/s^2 . This 1 kg m/s^2 is given the name Newton and the symbol 'N'.
  Thus, in your case, when we say 40N, we say 40 x 1 N that is 40 x 1 kg m/s^2 . This is why they're equal.
  
  Hope this helps, and sorry for such a lengthy explanation. I seem incapable of explaining in short.
  Button navigates to signup page
  (8 votes)
disantojoshua
Posted 2 years ago. Direct link to disantojoshua's post “so if I get this right, M...”
so if I get this right, Momentum and force are correlated?
since by my understanding saying 40 Netowns is the same as saying 40 kg * m/s^2 momentum.

fun fact: a force of 40Newtons is around 4KG of weight force.
1 meter / second is 3.60km/h
Button navigates to signup pageButton navigates to signup page
(6 votes)
Answer
- oswin.cervantes1551
  Posted 2 years ago. Direct link to oswin.cervantes1551's post “Force would be the rate o...”
  Force would be the rate of change of momentum.
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  (3 votes)
kea241199
Posted 2 years ago. Direct link to kea241199's post “In the last bullet it say...”
In the last bullet it says, "Momentum is conserved in the direction of Fₙₑₜ..." is it implied here that Fₙₑₜ = zero because conservation of momentum only applies when the net external force is zero?
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- Krithik
  Posted a year ago. Direct link to Krithik's post “yes that is right”
  yes
  that is right
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JJ999
Posted 2 years ago. Direct link to JJ999's post “Can anyone help me with t...”
Can anyone help me with this question:
Two model cars collide and then move together in one dimension. Car 1 has a mass of 2 kg and an initial velocity of 2m/s. Car 2 has a mass of 1 kg 1, point, and an initial velocity of -3 m/s before two model cars have a perfectly inelastic collision. What is their final velocity immediately after the collision?
(This is actually a question in the practice, but I did not understand their solution.)
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- Janice Tang
  Posted a year ago. Direct link to Janice Tang's post “I haven't encountered a p...”
  I haven't encountered a problem like this, I think in this unit the problem will give you one of the final momentums/velocities or (imply) that they are moving with the same momemtum/velocity. Otherwise I don't think this problem is designed for momemtum conservation.
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  (1 vote)
MaxS0348
Posted 8 months ago. Direct link to MaxS0348's post “Im having trouble underst...”
Im having trouble understanding conservation of momentum,
I understand the other lessons well but not this one.
Ive watched and read the articles and videos, can someone explain in simpler terms.
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(3 votes)
Answer
- Olivia Smith
  Posted 4 months ago. Direct link to Olivia Smith's post “Momentum is not gained or...”
  Momentum is not gained or lost. The initial or first momentum should equal the last momentum. This is only if there are no external forces applied
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  (3 votes)
dena escot
Posted a year ago. Direct link to dena escot's post “could you explain more "T...”
could you explain more "The change in velocity due to a net force will increase the longer that force acts on an object"

and in strikers example is the push off force internal or external force? I do not understand

and how are the forces acting between masses within a system cancel in pairs ? I knew from the newton's third law the pair force does not cancel each other
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(1 vote)
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s
Posted a year ago. Direct link to s's post “if the external force on ...”
if the external force on an isolated system is supposed to be -0- and the internal force does not affect the momentum how would force affect the momentum
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(1 vote)
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- Rosemary Monson
  Posted a year ago. Direct link to Rosemary Monson's post “It helps to have the exte...”
  It helps to have the external force equal 0 so that it does not have an effect on the system and we can just focus on the variables inside the system.
  The internal force does affect the momentum in a system.
  For example: (the objects IN the system are the hand and notebook) when a hand pushes a notebook across a desk, assuming the effect of friction and gravity(external forces) are negligible, the hand's momentum is the FORCE (in Newtons) applied to push the notebook multiplied by the time(usually in seconds) during which that force was applied.
  Comment on Rosemary Monson's post “It helps to have the exte...”
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David Ratliff
Posted 3 months ago. Direct link to David Ratliff's post “i watched the video 3 or ...”
i watched the video 3 or 4 times and I dont get it,it may be because im tired,but still i dont understand Sal shouldv explained it
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