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Conservation of momentum in one dimension

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Intros
Lessons
  1. Introduction to conservation of momentum in one dimension:
  2. Meaning of conservation of momentum
  3. Deriving conservation of momentum from Newton's third law
  4. Meaning of closed/open systems and identifying conservation of momentum problems
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Examples
Lessons
  1. ∑p⃗i=∑p⃗f:\bold{\sum\vec{p}_i = \sum\vec{p}_f}: Objects that bounce apart after collision
    1. A 0.200 kg billiard ball travelling 7.00 m/s to the right collides with a stationary 0.0450 kg golf ball. The velocity of the billiard ball after collision is 4.43 m/s [right]. What is the velocity of the golf ball after collision?
    2. A 2.20 kg ball rolling 1.50 m/s [E] collides head-on with a ball rolling 2.40 m/s [W]. The 2.20 kg ball rolls away at 1.00 m/s [W] after the collision, and the second ball rolls 1.80 m/s [E]. What is the mass of the second ball?
    3. 4500 kg train car A travels at 6 m/s [E]. It collides with 3750 kg train car B which is travelling 3.2 m/s [E] on the same track. After the collision, train car A travels at 3.5 m/s [E]. Find the final velocity of train car B.
    4. A rifle points [E] at a 3.40 kg wood block. It fires a 22.0 g bullet travelling at 460.0 m/s, which passes through the block and continues at 299 m/s. Find the velocity of the wood block when the bullet leaves.
  2. ∑p⃗i=∑p⃗f:\bold{\sum\vec{p}_i = \sum\vec{p}_f}: Objects that stick together after collision
    1. A rifle points [E] at a 3.40 kg wood block. It fires a 22.0 g bullet travelling at 460.0 m/s, which embeds in the block. Find the velocity of the bullet and the wood block after embedding.
    2. An 80.0 kg hockey goalie is gliding 0.230 m/s [W] when he catches an incoming 162 g puck travelling [W]. If the goalie then travels at 0.300 m/s [W], what is the velocity of the puck before he catches it?
    3. A 2575 kg truck travelling at 15.0 m/s right collides with a 1895 kg car reversing at 1.00 m/s to the left. The vehicles stick together after the collision.
      1. What is the velocity of the vehicles after the collision?
      2. If the crashed cars skid for 4.30 s after crashing, what is the average force of friction from the road acting on them?
  3. ∑p⃗i=∑p⃗f:\bold{\sum\vec{p}_i = \sum\vec{p}_f}: Objects that explode apart
    1. A 68 000 kg rocket initially at rest in space fires a thruster which expels 43 kg of gas at 730 m/s [left]. Find the final velocity of the rocket.
    2. Two paddlers dock their canoe. The canoe is stationary when 72 kg paddler A steps out at 2.4 m/s forwards. This causes the canoe and 59 kg paddler B to move at a speed of 1.8 m/s. Find the direction that paddler B is moving in after paddler A steps out, and the mass of the canoe.
    3. A 3400 kg rail car carries a 200 kg cannon and a 15 kg cannonball along a level rail at 9.5 m/s [E]. The cannon fires the cannonball at 478 m/s [E]. Find the velocity of the rail car and cannon after firing.
Topic Notes
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Introduction to Conservation of Momentum in One Dimension

Conservation of momentum in one dimension is a fundamental principle in physics that plays a crucial role in understanding collisions and other interactions between objects. The introduction video provides a clear and engaging overview of this concept, making it easier for students to grasp its significance. Momentum, defined as the product of an object's mass and velocity, is a conserved quantity in closed systems. This means that the total momentum before and after a collision remains constant, assuming no external forces are acting on the system. In one-dimensional collisions, objects move along a straight line, simplifying the analysis. The conservation of momentum principle applies to various types of collisions, including elastic and inelastic collisions. By studying this concept, students can predict the outcomes of collisions and gain insights into the behavior of objects in motion. Understanding conservation of momentum is essential for solving problems in mechanics and forms the basis for more advanced topics in physics.

Understanding Momentum Conservation

Momentum conservation is a fundamental principle in physics that plays a crucial role in understanding the behavior of objects during collisions and interactions. This concept states that the total momentum of a closed system remains constant over time, regardless of the internal forces acting between the objects within the system. To illustrate this principle, let's consider the example of two balls colliding.

Imagine two billiard balls rolling towards each other on a smooth table. Each ball has its own momentum, which is the product of its mass and velocity. As they collide, their individual momenta change, but the total momentum of the system remains the same. This is where momentum vectors come into play. We can represent the momentum of each ball as a vector, with the direction indicating the ball's motion and the magnitude representing the product of its mass and speed.

Before the collision, we can add these momentum vectors to find the total momentum of the system. After the collision, even though the individual momenta of the balls may have changed, the sum of their new momentum vectors will equal the total momentum before the collision. This vector addition demonstrates the conservation of momentum in action.

The concept of momentum conservation was initially discovered through empirical observations. Scientists and philosophers, including René Descartes and Christiaan Huygens, noticed patterns in the behavior of colliding objects that suggested a conserved quantity. These observations led to the formulation of the principle of momentum conservation, which was later refined and mathematically formalized.

The mathematical derivation of momentum conservation stems from Newton's second law momentum, which states that for every action, there is an equal and opposite reaction. When two objects interact, the forces they exert on each other are equal in magnitude but opposite in direction. This symmetry in forces leads to the conservation of momentum.

To understand this derivation, consider two objects, A and B, colliding. The force exerted by A on B is equal and opposite to the force exerted by B on A. We can express this mathematically as F_AB = -F_BA. Now, recall Newton's second law momentum, which states that force equals mass times acceleration (F = ma). Applying this to our collision scenario, we get:

m_A * a_A = -m_B * a_B

Rearranging this equation and integrating with respect to time, we arrive at:

m_A * (v_A_final - v_A_initial) = -m_B * (v_B_final - v_B_initial)

This equation demonstrates that the change in momentum of object A is equal and opposite to the change in momentum of object B, thus proving the conservation of total momentum in the system.

The principle of momentum conservation has far-reaching applications in various fields of physics and engineering. It is used to analyze complex systems, from subatomic particle collisions to the motion of celestial bodies. In everyday life, we can observe momentum conservation in sports, such as the recoil of a gun or the motion of billiard balls on a pool table.

Understanding momentum conservation is crucial for solving problems involving collisions and interactions between objects. It allows us to predict the outcomes of these interactions without needing to know the details of the forces involved during the collision process. This makes it an invaluable tool in physics and engineering, simplifying complex problems and providing insights into the behavior of physical systems.

In conclusion, momentum conservation is a powerful principle that emerges from the fundamental laws of physics. Its empirical discovery and subsequent mathematical derivation from Newton's third law have provided us with a robust framework for understanding and predicting the behavior of interacting objects. By utilizing momentum vectors and applying the principle of conservation, we can analyze complex systems and gain valuable insights into the nature of motion and interaction in the physical world.

Deriving the Conservation of Momentum Equation

The conservation of momentum equation is a fundamental principle in physics that stems from Newton's third law of motion. To understand its derivation, we must start with this law and explore how it leads to the concept of momentum conservation. Newton's third law states that for every action, there is an equal and opposite reaction. This principle forms the basis for our understanding of momentum and its conservation.

Let's begin with two objects, A and B, interacting with each other. According to Newton's third law, the force exerted by object A on object B (FAB) is equal in magnitude but opposite in direction to the force exerted by object B on object A (FBA). Mathematically, we can express this as:

FAB = -FBA

Now, let's consider Newton's second law of motion, which states that force is equal to the rate of change of momentum. For object A, we can write:

FA = dpA/dt

Where pA is the momentum of object A, and t is time. Similarly, for object B:

FB = dpB/dt

Since the forces acting on both objects are equal and opposite, we can combine these equations:

dpA/dt = -dpB/dt

This equation shows that the rate of change of momentum for object A is equal and opposite to the rate of change of momentum for object B. To derive the conservation of momentum equation, we need to integrate both sides of this equation with respect to time:

dpA = -dpB

Performing this integration from an initial time t1 to a final time t2, we get:

pA,final - pA,initial = -(pB,final - pB,initial)

Rearranging this equation, we arrive at the conservation of momentum equation:

pA,initial + pB,initial = pA,final + pB,final

This equation states that the total momentum of a closed system before an interaction is equal to the total momentum after the interaction. It's important to note that this principle applies to closed systems where no external forces are acting.

The concept of impulse and momentum change plays a crucial role in this derivation. Impulse is defined as the product of force and the time interval over which it acts. Mathematically, impulse (J) is expressed as:

J = F * Δt

Impulse is also equal to the change in momentum:

J = Δp = pfinal - pinitial

This relationship between impulse and momentum change is fundamental to understanding how forces affect the motion of objects over time. In the context of our derivation, the impulse experienced by object A is equal and opposite to the impulse experienced by object B, which leads to the conservation of momentum.

The final conservation of momentum equation can be written in vector form as:

Σpinitial = Σpfinal

Where Σ represents the sum of all momenta in the system. This equation holds true for any number of objects in a closed system, not just the two we considered in our derivation.

Understanding the components of this equation is crucial. The momentum of each object is calculated as the product of its mass and velocity (p = mv). Therefore, the conservation of momentum equation

Applications and Properties of Momentum Conservation

The conservation of momentum is a fundamental principle in physics that has wide-ranging applications and properties. This principle states that the total momentum of a closed system remains constant over time, regardless of the interactions between its components. Understanding the various applications and properties of the conservation of momentum equation is crucial for analyzing and predicting the behavior of objects in motion.

One of the key properties of the conservation of momentum equation is its applicability in both one and two dimensions. In one-dimensional scenarios, such as objects moving along a straight line, the equation simplifies to p1 + p2 = p1' + p2', where p represents the momentum of each object before and after an interaction. For example, consider a head-on collision between two cars on a straight road. The total momentum before the collision must equal the total momentum after the collision, even if the individual velocities of the cars change.

In two-dimensional situations, the conservation of momentum applies separately to each dimension. This property is particularly useful when analyzing collisions or explosions where objects move in multiple directions. For instance, in a game of billiards, when the cue ball strikes another ball at an angle, the momentum is conserved in both the x and y directions independently. This allows us to predict the trajectories of both balls after the collision.

Another important property of the conservation of momentum equation is its ability to handle any number of objects. Whether dealing with two particles or a complex system of multiple bodies, the principle remains valid. This makes it an invaluable tool in analyzing complex systems such as particle accelerators, where numerous subatomic particles interact, or in astrophysics, where multiple celestial bodies influence each other's motion.

The conservation of momentum equation is equally applicable to both collisions and explosions. In collisions, objects come together and potentially separate, while in explosions, a single object breaks apart into multiple pieces. Despite these differences, the total momentum of the system remains constant in both cases. For example, when a firecracker explodes, the fragments fly off in different directions, but their total momentum equals the initial momentum of the intact firecracker.

To illustrate the versatility of momentum conservation, consider a rocket launch. As the rocket expels hot gases downward, it gains upward momentum. The total momentum of the system (rocket plus expelled gases) remains constant, demonstrating how the principle applies to propulsion systems. This same concept is used in the design of jet engines and even in the propulsion mechanisms of some marine animals.

In the realm of particle physics, the conservation of momentum plays a crucial role in analyzing subatomic collisions. When particles collide in accelerators, scientists use momentum conservation to deduce the properties of newly created particles, even those that are too short-lived to detect directly. This application has been instrumental in discovering new elementary particles and validating theoretical predictions.

The principle also finds applications in everyday scenarios. For instance, when a person jumps from a boat to a dock, the boat moves slightly in the opposite direction. This is a direct consequence of momentum conservation, as the total momentum of the person-boat system must remain constant. Similarly, the recoil experienced when firing a gun is another practical example of this principle in action.

In sports, momentum conservation explains many phenomena. The follow-through in tennis or golf is partly based on this principle, as it helps transfer maximum momentum to the ball. In martial arts, techniques often involve using an opponent's momentum against them, effectively redirecting rather than opposing the incoming force.

The conservation of momentum is not limited to classical mechanics; it also holds in quantum mechanics and relativistic physics. In quantum systems, it leads to important consequences such as the uncertainty principle. In relativistic scenarios, while the formula for momentum changes, the conservation principle still holds, playing a crucial role in understanding high-energy particle interactions and cosmic phenomena.

In conclusion, the conservation of momentum equation is a powerful and versatile tool in physics. Its applicability across dimensions, ability to handle multiple objects, and validity for both collisions and explosions make it indispensable in various fields of study and practical applications. From the microscopic world of particles to the macroscopic realm of celestial bodies, this principle continues to be a cornerstone of our understanding of the physical universe.

When is Momentum Conserved?

Momentum conservation is a fundamental principle in physics, but it's crucial to understand the specific conditions under which it applies. The conservation of momentum states that the total momentum of a closed system remains constant over time. However, in real-world scenarios, we often encounter situations where momentum appears not to be conserved. To fully grasp this concept, we need to explore the differences between open and closed systems and how external forces affect momentum conservation.

A closed system is one in which no external forces act on the objects within it. In such a system, the total momentum before and after any interaction remains constant. This is the ideal scenario where momentum conservation is perfectly observed. For example, in a collision between two objects in space, far from any gravitational influences, the total momentum of the system would be conserved.

On the other hand, an open system is one where external forces can act on the objects within it. In open systems, momentum may appear not to be conserved when we only consider the visible objects involved. However, it's important to note that momentum is still conserved in the broader context; it's just being transferred to the environment or other objects not immediately visible or considered part of the system.

External forces play a significant role in the apparent non-conservation of momentum in many real-world scenarios. Two of the most common external forces that affect momentum are friction and air resistance. Friction occurs when objects move against each other or along surfaces, while air resistance is the force exerted by air on moving objects.

Let's consider a simple example of a ball rolling on a rough surface. As the ball rolls, it gradually slows down and eventually comes to a stop. At first glance, this might seem like a violation of momentum conservation. However, what's actually happening is that the ball's momentum is being transferred to the surface and the surrounding air molecules through friction and air resistance.

Friction converts some of the ball's kinetic energy into heat energy, which is dissipated into the environment. The microscopic interactions between the ball and the surface also transfer tiny amounts of momentum to the Earth. Similarly, air resistance causes the ball to transfer momentum to the air molecules it collides with as it moves.

In open systems, momentum is continually being exchanged with the environment. This transfer of momentum can occur through various mechanisms, such as collisions with air molecules, friction with surfaces, or even the emission of particles or radiation. For instance, when a rocket launches, it expels hot gases at high velocities, transferring momentum to these gases and propelling itself forward.

It's worth noting that even in cases where momentum appears to be lost due to external forces, it is actually being distributed over a larger system. The total momentum of the universe, considered as the ultimate closed system, remains constant. This broader perspective helps reconcile the apparent loss of momentum in everyday situations with the fundamental principle of momentum conservation.

Understanding the distinction between open and closed systems is crucial for accurately analyzing momentum conservation in various scenarios. In practical applications, such as engineering or sports, accounting for external forces like friction and air resistance is essential for making accurate predictions and designing efficient systems.

In conclusion, momentum is always conserved in closed systems, where no external forces are present. In open systems, which are more common in our everyday experiences, momentum may appear not to be conserved due to the influence of external forces like friction and air resistance. However, this apparent non-conservation is actually a transfer of momentum to the surrounding environment. By considering the broader system and accounting for these external influences, we can reconcile real-world observations with the fundamental principle of momentum conservation.

Practical Applications of Conservation of Momentum

Conservation of momentum is a fundamental principle in physics that finds numerous practical applications in real-world scenarios. This principle states that the total momentum of a closed system remains constant over time, making it a powerful tool for analyzing and predicting the behavior of objects in various situations. In this section, we'll explore practical situations where conservation of momentum can be applied, discuss its use in closed systems and short-duration events, and provide guidance on when to use (and when not to use) this principle in problem-solving.

One of the most common applications of conservation of momentum is in the analysis of collisions. Whether it's studying car crashes, billiard ball interactions, or atomic particle collisions, this principle allows scientists and engineers to predict the outcomes of these events. For instance, in vehicle safety testing, conservation of momentum helps designers understand how different materials and structures absorb and redistribute energy during a crash, leading to improved safety features.

Another practical application is in rocketry and space exploration. The principle explains how rockets can propel themselves in the vacuum of space by expelling mass in one direction, resulting in an equal and opposite momentum change for the rocket. This understanding is crucial for designing efficient propulsion systems and planning space missions.

In sports, conservation of momentum plays a significant role in understanding and optimizing performance. For example, in diving or gymnastics, athletes use this principle to control their rotations by changing their body positions. Similarly, in martial arts, practitioners leverage momentum conservation to maximize the force of their strikes or to redirect an opponent's energy.

When dealing with closed systems, conservation of momentum becomes particularly powerful. A closed system is one where no external forces act on the objects within it. In such cases, the total momentum before and after any internal interactions (like collisions or explosions) remains constant. This principle is often applied in analyzing isolated systems such as: - Two ice skaters pushing off each other - A cannon firing a projectile (considering the cannon and ball as a system) - A firework exploding in mid-air

The conservation of momentum is especially useful when analyzing events that occur over very short time periods. During these brief moments, the impulse (change in momentum) can be significant, while the overall displacement of objects might be negligible. This makes momentum conservation more practical than energy conservation in such scenarios. Examples include: - The instant of impact in a car collision - The moment a baseball bat strikes a ball - The split second when two subatomic particles collide in a particle accelerator

In problem-solving, conservation of momentum is most effectively used when: 1. The system can be considered closed (no significant external forces) 2. The event occurs over a very short time period 3. Information about velocities before or after an event is known or required 4. The masses of the objects involved are known or can be determined 5. Other conservation laws (like energy conservation) are difficult to apply due to unknown factors

However, it's important to recognize situations where conservation of momentum might not be the best approach: 1. When significant external forces are present (e.g., friction over long distances) 2. In scenarios where energy dissipation is a crucial factor (e.g., inelastic collisions where deformation is significant) 3. When dealing with systems that involve continuous force application over extended periods 4. In cases where rotational motion is a significant factor, and linear momentum alone is insufficient

To effectively use conservation of momentum in problem-solving, follow these steps: 1. Identify the system and ensure it can be treated as closed 2. Determine the relevant masses and initial velocities 3. Write out the conservation of momentum equation (total initial momentum = total final momentum) 4. Solve for the unknown variables, typically final velocities 5. Check your answer for reasonableness and units consistency

In conclusion, conservation of momentum is a versatile and powerful principle with wide-ranging applications in physics and engineering. By understanding when and how to apply this concept, problem-solvers can efficiently analyze complex systems, predict outcomes of collisions and explosions, and gain insights into the behavior of objects in various practical situations. Whether you're designing safety systems, optimizing athletic performance, or exploring the cosmos, conservation of momentum remains an indispensable tool in the physicist's and engineer's arsenal.

Conclusion

In summary, conservation of momentum in one dimension is a fundamental principle in physics. Key points include: the total momentum of a closed system remains constant, momentum is conserved in collisions and explosions, and the concept applies to both elastic and inelastic collisions. Understanding this concept is crucial for further studies in physics, as it forms the basis for more complex scenarios in multiple dimensions and advanced topics like quantum mechanics. To reinforce your understanding, practice applying these principles in problem-solving exercises. Start with simple one-dimensional problems and gradually progress to more challenging scenarios. Explore real-world applications, such as car crashes or rocket propulsion, to see how momentum conservation plays out in practical situations. By mastering this concept, you'll build a strong foundation for advanced physics studies and develop critical analytical skills. Remember, the ability to apply momentum conservation principles is essential for success in physics and related fields.

Introduction to Conservation of Momentum in One Dimension: Meaning of Conservation of Momentum

In this section, we will explore the concept of conservation of momentum in one dimension. We will break down the meaning of conservation of momentum and understand its implications through a step-by-step approach.

Step 1: Understanding Momentum

Momentum is a fundamental concept in physics, defined as the product of an object's mass and its velocity. It is a vector quantity, meaning it has both magnitude and direction. In mathematical terms, momentum (p) is expressed as:

p = m * v

where m is the mass of the object and v is its velocity. The direction of the momentum vector is the same as the direction of the velocity vector.

Step 2: Conservation of Momentum

The principle of conservation of momentum states that the total momentum of a closed system remains constant if no external forces act on it. This means that in any process, such as a collision, the total momentum before the event is equal to the total momentum after the event. Mathematically, this can be expressed as:

pinitial = pfinal

In a one-dimensional system, this principle simplifies the analysis of collisions and other interactions.

Step 3: Analyzing a Simple Collision

To illustrate the conservation of momentum, consider a simple collision between two balls. Before the collision, each ball has its own momentum, represented by momentum vectors. Let's denote the momentum of the pink ball as ppink and the momentum of the blue ball as pblue.

When the balls collide, they exert forces on each other, causing changes in their velocities and, consequently, their momenta. However, the total momentum of the system (pink ball + blue ball) remains unchanged. This can be visualized by adding the momentum vectors of the two balls before and after the collision:

ppink, initial + pblue, initial = ppink, final + pblue, final

Step 4: Vector Addition of Momentum

To further understand the conservation of momentum, we can use vector addition. By adding the momentum vectors of the pink and blue balls tip-to-tail, we can find the overall momentum of the system before the collision. After the collision, we repeat the process to find the overall momentum again. If the total momentum vectors before and after the collision are equal, it confirms that momentum is conserved.

This vector addition method helps visualize how the individual momenta of the colliding objects combine to maintain the total momentum of the system.

Step 5: Empirical Evidence and Mathematical Proof

The concept of conservation of momentum was initially discovered through empirical observations. Physicists conducted experiments by colliding objects and measuring their velocities before and after the collisions. They consistently found that the total momentum remained the same, leading to the formulation of the conservation of momentum principle.

Additionally, mathematical analysis can demonstrate why momentum must be conserved. By examining the forces and interactions during the collision, we can show that the changes in momentum of the individual objects cancel out, resulting in no net change in the total momentum of the system.

Step 6: Practical Applications

The principle of conservation of momentum has numerous practical applications in various fields, including engineering, astrophysics, and everyday life. For example, it is used to analyze car crashes, design safety features, and understand the behavior of celestial bodies in space.

Understanding and applying the conservation of momentum allows us to predict the outcomes of collisions and interactions, making it a crucial concept in both theoretical and applied physics.

Conclusion

In summary, the conservation of momentum in one dimension is a fundamental principle in physics that states the total momentum of a closed system remains constant if no external forces act on it. By analyzing simple collisions and using vector addition, we can visualize and confirm this principle. Empirical evidence and mathematical analysis further support the conservation of momentum, making it a key concept with wide-ranging applications.

FAQs

  1. What is the conservation of momentum in one dimension?

    Conservation of momentum in one dimension is a fundamental principle in physics stating that the total momentum of a closed system remains constant before and after a collision or interaction, assuming no external forces are acting on the system. In one-dimensional scenarios, objects move along a straight line, and their momentum is calculated as the product of mass and velocity (p = mv).

  2. How does the conservation of momentum apply to collisions?

    In collisions, the conservation of momentum principle ensures that the total momentum of the system before the collision equals the total momentum after the collision. This applies to both elastic collisions (where kinetic energy is conserved) and inelastic collisions (where kinetic energy is not conserved). The principle allows us to predict the final velocities of objects involved in collisions when given their initial velocities and masses.

  3. What is the difference between elastic and inelastic collisions in terms of momentum conservation?

    Both elastic and inelastic collisions conserve momentum. In elastic collisions, kinetic energy is also conserved, and objects bounce off each other without deformation. In inelastic collisions, kinetic energy is not conserved (some is converted to heat or deformation), but momentum is still conserved. The key difference is that in perfectly inelastic collisions, the objects stick together after collision, moving with a common final velocity.

  4. How can I apply the conservation of momentum principle to solve physics problems?

    To apply the conservation of momentum principle: 1. Identify the system and ensure it's closed (no external forces). 2. Determine the masses and initial velocities of objects involved. 3. Write the conservation of momentum equation: m1v1 + m2v2 = m1v1' + m2v2' (where primed velocities are after collision). 4. Solve for unknown velocities using the equation and given information. 5. Check your answer for reasonableness and correct units.

  5. Are there any limitations to the conservation of momentum principle?

    While the conservation of momentum is a fundamental principle, it has limitations in practical applications: 1. It only applies to closed systems with no external forces. 2. In real-world scenarios, factors like friction and air resistance can affect momentum conservation over time. 3. For complex systems or rotational motion, additional principles may be needed for a complete analysis. 4. In relativistic scenarios (near light speed), classical momentum formulas need to be adjusted, though the conservation principle still holds.

Prerequisite Topics

Understanding the conservation of momentum in one dimension is a crucial concept in physics, but to fully grasp its significance, it's essential to have a solid foundation in several prerequisite topics. These fundamental concepts provide the necessary context and tools to comprehend the intricacies of momentum conservation.

At the core of this topic lies Newton's second law of motion, which establishes the relationship between force, mass, and acceleration. This law is fundamental to understanding how momentum changes over time and forms the basis for deriving the conservation of momentum principle. By mastering Newton's second law, students can better appreciate the forces at play during momentum conservation scenarios.

Another critical prerequisite is the concept of elastic and inelastic collisions. These types of collisions are prime examples of momentum conservation in action. Understanding the differences between elastic collisions, where kinetic energy is conserved, and inelastic collisions, where it is not, helps students apply the conservation of momentum principle to real-world situations.

The rate of change is another essential concept, particularly when considering the rate of change of momentum. This mathematical tool allows students to analyze how momentum varies over time, which is crucial for understanding impulse and its relationship to momentum change.

Speaking of which, the relationship between momentum and impulse is a key prerequisite. Impulse, being the change in momentum, directly ties into the conservation principle. Grasping this connection helps students understand how forces applied over time can affect an object's momentum while still adhering to the conservation law.

Lastly, while not directly related to linear momentum, understanding rotational kinetic energy and angular momentum provides a broader perspective on energy and momentum concepts. This knowledge allows students to draw parallels between linear and rotational systems, enhancing their overall comprehension of momentum conservation principles.

By thoroughly studying these prerequisite topics, students build a strong foundation for understanding the conservation of momentum in one dimension. Each concept contributes to a more comprehensive view of how objects interact and move in the physical world, making the study of momentum conservation not just more accessible, but also more meaningful and applicable to real-world scenarios.

In this lesson, we will learn:

  • Meaning of conservation of momentum
  • Deriving conservation of momentum from Newton's third law
  • Meaning of closed/open systems and identifying conservation of momentum problems
  • Problem solving with conservation of momentum in 1 dimension

Notes:

  • Momentum is a conserved quantity: the total momentum of a set of objects before an event (like a collision or explosion) is equal to total momentum after.
  • Conservation of momentum (∑p⃗i=∑p⃗f\sum\vec{p}_i = \sum\vec{p}_f)is a result of Newton's 3rd
    • Law (F⃗A=−F⃗B\vec{F}_A = -\vec{F}_B).
  • When talking about conservation of momentum, system is a name given to an object or set of objects that are being examined.
    • A closed system is an object or set of objects that are not affected by external forces (i.e. their motion is not changing due to forces from outside the system). Momentum is conserved in a closed system.
      • A system can have external forces acting on it while still being closed, as long as those forces are balanced. A ball rolling across a frictionless table would be considered a closed system even though gravity and normal force act on the ball. Gravity and normal force are balanced, so they are not causing the ball to accelerate, and momentum is conserved.
    • An open system is an object or set of objects that are affected by external forces (i.e. their motion does change due to forces from outside the system). Momentum is not conserved in an open system.
      • If the ball from the earlier example rolls off the edge of the frictionless table and is accelerated by gravity towards the earth, then it is no longer considered a closed system. The system is open and gaining momentum from the acceleration due to gravity.

Momentum

p⃗=mv⃗:\vec{p} = m \vec{v}: momentum, in kilogram meters per second (kg∙m/s)

m:m: mass, in kilograms (kg)

v⃗:\vec{v}: velocity, in meters per second (m/s)


Conservation of Momentum

∑p⃗i=∑p⃗f\sum\vec{p}_i = \sum\vec{p}_f

p⃗i:\vec{p}_i: initial momentum, in kilogram meters per second (kg·m/s)

p⃗f:\vec{p}_f: final momentum, in kilogram meters per second (kg·m/s)


Impulse

J⃗=F⃗Δt=Δp⃗=m(v⃗f−v⃗i\vec{J} = \vec{F} \Delta t = \Delta \vec{p} = m( \vec{v}_f - \vec{v}_i)

J⃗:\vec{J}: impulse, in newton seconds (N∙s)

F⃗:\vec{F}: net force acting on an object, in newtons (N)

Δt:\Delta t: the length of time for which the force acts, in seconds (s)

Δp⃗:\Delta \vec{p}: change in momentum of an object, in kilgram meters per second (kg∙m/s)