What Physical Quantities Are Conserved In This Collision? Discover the Fundamental Laws of Physics

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Have you ever wondered why some collisions result in certain outcomes while others have completely different results? The answer lies in the fundamental laws of physics that govern our world. These laws dictate what physical quantities are conserved during a collision, such as momentum and energy.

Understanding these conservation laws is crucial not only for theoretical purposes but also in practical applications such as engineering and transportation safety. By knowing which physical quantities are conserved in a collision, we can predict and prevent potential accidents and improve designs to maximize efficiency and minimize damage.

In this article, we will explore various types of collisions and examine how physical quantities like momentum, energy, and angular momentum are conserved. We will dive into the mathematical equations that describe these principles and see how they apply to real-life scenarios.

“We cannot ignore the importance of understanding these fundamental laws of physics if we want to succeed in advancing our technology and society.” -Unknown

So whether you’re a curious student or a seasoned physicist, join us on this journey to discover what physical quantities are conserved in a collision and unlock the secrets of the universe.


Definition of Mass

Mass is a fundamental physical quantity that measures the amount of matter an object contains. It is a scalar value that does not depend on the object’s location and describes its resistance to acceleration. In simpler terms, it is the measure of how heavy an object is.

In classical mechanics, mass is often defined as the ratio of force to acceleration (F = ma). Thus, it can be expressed in units related to force and acceleration, such as kg*m/s² or N*s²/m.

Units of Mass

The most commonly used unit for mass measurement is kilograms (kg) in the International System of Units (SI), which is based on the mass of a platinum-iridium kilogram prototype kept at the International Bureau of Weights and Measures in France. Other SI units include gram (g) and milligram (mg).

Other systems of measurement for mass also exist. For example, in the United States Customary Units system, the pound (lb) and ounce (oz) are used, while in Britain, the Stone, Pounds and Ounces (“stones”) system is still occasionally encountered. There is no mathematical relationship between these units equivalent to the relationship between metric units, but conversion factors can easily be found online or in reference books.

Conservation of Mass

The principle of conservation of mass states that the total mass of a closed system will remain constant, regardless of any internal changes it undergoes. This means that if there is no transfer of matter across the boundaries of a system, then the total mass of the system remains unchanged before and after a process occurs.

This principle plays a significant role in many fields of science, including physics, chemistry and engineering. In fact, it is a fundamental aspect of science that allows us to analyse processes and evaluate their effects on the external environment.

The law of conservation of mass can be traced back to Antoine Lavoisier’s Law of Conservation of Matter in 1785 when he famously stated “Nothing is lost, nothing is created, everything is transformed”. This idea was later extended by Einstein with his famous equation E=mc² which showed how mass and energy are interchangeable.

“Mass-energy equivalence arises fundamentally from the unification of space and time into spacetime, and also holds true in systems where gravity is not negligible.” -Albert Einstein

Mass is an important physical quantity in our everyday lives and plays a crucial role in many areas of science. Its units are well-defined, and its conservation is taken for granted in most scientific fields. Understanding its properties can provide insight into the workings of nature itself.


Definition of Momentum

Momentum is a measurement of motion, calculated as the product of an object’s mass and its velocity. In physics, momentum is represented by the symbol p, and it is one of the fundamental quantities used to describe the behavior of objects in motion.

The unit of momentum is kilogram meter per second (kg⋅m/s), which can be abbreviated as Ns or simply p. Essentially, momentum tells us how difficult it would be to stop a moving object relative to its mass and velocity. For example, a bowling ball traveling at 10 meters per second has more momentum than a golf ball traveling at the same speed because it has a greater mass.

“Momentum is conserved; that is, the total momentum of any closed system of objects (which has no interactions with external agents) remains constant.” -Encyclopedia Britannica

Conservation of Momentum

In any collision between two objects, the total momentum before the collision must equal the total momentum after the collision. This principle is known as the conservation of momentum, and it applies to both elastic and inelastic collisions.

Elastic collisions occur when two objects collide and bounce off each other without losing energy. Inelastic collisions, on the other hand, occur when two objects collide and stick together, losing some of their kinetic energy in the process.

To illustrate the conservation of momentum, consider the example of two billiard balls colliding. If Billiard Ball A is initially traveling at 5 meters per second towards Billiard Ball B, and Billiard Ball B is stationary, then the initial momentum is p1 = mAvA + mBvB = mA * 5 m/s + mB * 0 m/s = mA * 5 m/s. After the collision, let’s say that the two billiard balls stick together and move off at a combined velocity of 2 meters per second. The final momentum is p2 = (mA + mB)v2 = (mA + mB) * 2 m/s. To determine if momentum has been conserved, we need to compare p1 and p2. If they are equal, then the conservation of momentum has been demonstrated.

Impulse and Momentum

Another important concept related to momentum is impulse, which refers to the change in momentum that occurs when an object experiences a force over a period of time. Mathematically, impulse can be calculated as the integral of the force with respect to time. This means that increasing the amount of time over which a force is applied can increase the impulse, even if the same magnitude of force is used.

The relationship between impulse and momentum is described by the formula FΔt = Δp, where F is the force applied, Δt is the duration of the force application, and Δp is the change in momentum that results. Essentially, this equation tells us that applying a constant force for a longer time will result in a greater change in momentum than applying the same force for a shorter time.

“The impulse experienced by an object is always equal to the change in momentum of that object.” -Khan Academy


Energy is the ability to do work. It is also defined as the capacity of a physical system to perform work. Energy can be converted from one form to another, but it can never be created or destroyed; this statement is known as the law of conservation of energy.

Forms of Energy

There are various forms of energy, and they all have different qualities and characteristics that define them:

  • Thermal Energy: This type of energy is associated with the temperature of an object, such as heat generated by friction.
  • Mechanical Energy: This refers to the energy stored in objects that are under tension or compression. A stretched spring has potential mechanical energy.
  • Electrical Energy: The electrical flow of charged particles generates electrical energy.
  • Chemical Energy: Chemical reactions release energy as a result of breaking or forming bonds between atoms or molecules.

Conservation of Energy

The principle of conservation of energy states that energy cannot be created or destroyed; it can only be transferred from one form to another. Therefore, the total amount of energy in a closed system remains constant over time. This law applies to all physical systems, from simple experiments in a laboratory to complex interactions among planets and stars.

“The principle of the conservation of energy is one of the most fundamental laws of physics and is a cornerstone in our understanding of the natural world.” -National Renewable Energy Laboratory

In practice, some energy losses occur due to factors like air resistance, friction, or sound waves. However, those losses do not affect the overall balance of energy. For example, when a ball falls from a height, some of its potential energy transforms into kinetic energy. The faster the ball moves, the more kinetic energy it has, but it also experiences air resistance that reduces this energy.

Work and Energy

Both work and energy are closely related concepts in physics. Work is defined as the force required to move an object over a distance, while energy refers to its ability to perform such work. Both terms have units measured in Joules (J).

“The distinction between work and energy is subtle but important.” -MIT News

If an external force acts on an object to make it move, then work has been done on the object. If we lift a box off the ground, we do work on it against gravity. This work requires energy (in this case, chemical energy from our muscles), which ultimately comes from food consumed by our bodies.

The relationship between work and energy can be expressed through the work-energy theorem, which states that the net work done by all forces acting on an object equals the change in its total mechanical energy (sum of potential and kinetic energies).

“The work-energy theorem is one of the most powerful tools in classical mechanics.” -The Physics Classroom

In other words, if all forces cancel out each other, or if no external force is present, the total mechanical energy remains constant. As per the principle of conservation of energy, energy cannot vanish from the system; it must exist in either form, kinetic, or potential energy. For example, when a pendulum swings back and forth, its total mechanical energy transforms between kinetic and potential forms, but their sum always stays the same.

The concept of energy is essential in understanding how physical systems behave and how much work they can perform. Different types of energy exist and can be converted from one form to another, but the total amount of energy in a closed system remains constant over time. Work is defined as the force required to move an object over distance, while energy refers to its capacity to perform work. The principle of conservation of energy governs energy transformations and exchanges among physical systems and relates them to concepts like potential and kinetic energy.

Angular Momentum

Angular momentum is a physical quantity that describes the rotational motion of an object. It measures how much rotation an object has and how difficult it is to change its state of rotation. The angular momentum of an object depends on both its mass and how fast it is spinning.

Definition of Angular Momentum

The formula for angular momentum is L = Iω, where L represents angular momentum, I represents moment of inertia, and ω represents angular velocity. Moment of inertia can be seen as a measure of how difficult it is to rotate an object around a particular axis. For example, a long thin rod will have a different moment of inertia than a solid sphere of uniform density with the same mass. When it comes to calculating angular momentum, we must use the direction of angular velocity since it is a vector quantity.

“The total angular momentum of any isolated system remains constant – or is conserved – unless acted upon by an external torque.” – Hyperphysics

Conservation of Angular Momentum

Similar to the principle of conservation of linear momentum, the conservation of angular momentum states that the total angular momentum of an isolated system does not change over time unless acted upon by an external force. This means that if two objects collide, their initial angular momentum before the collision will equal their final angular momentum after the collision.

An everyday example of this phenomenon is when ice skaters spin faster, they move their limbs closer to their body, which decreases their moment of inertia, causing them to rotate faster due to the conservation of angular momentum. In astronomy, the conservation of angular momentum plays a crucial role in understanding how planets form from rotating disks of gas and dust.

Torque and Angular Momentum

To understand the relationship between torque and angular momentum, we must first define torque. Torque is the measure of a force’s ability to cause rotation around an axis. If we apply a perpendicular force on a lever arm or a wrench, it will rotate around its fixed point due to torque.

As we know from before, increasing torque changes an object’s rate of rotational motion. An increase in torque leads to an increase in angular acceleration which causes objects to spin faster and gain more angular momentum.

“Torque can change angular momentum just as force can change linear momentum.” – The Physics Classroom

Rotational Kinetic Energy

Rotational kinetic energy, also known as angular kinetic energy, is another physical quantity that relates to the motion of rotating objects. It expresses the amount of energy an object has due to its rotation around an axis.

The formula for rotational kinetic energy is K = 0.5Iω², where K represents rotational kinetic energy, I represents moment of inertia, and ω represents angular velocity. This formula tells us that objects with large moments of inertia require more energy to achieve the same angular velocity than objects with lower moments of inertia.

We can use this concept to understand how different objects move when they collide. In a collision between two objects, some fraction of their kinetic energy is lost, but it must go somewhere. In elastic collisions, the lost kinetic energy turns into heat, soundwaves, and other forms of energy, whereas, in non-elastic collisions, the lost energy may turn into deformation or chemical reactions.


Definition of Charge

Charge is a physical quantity that refers to the electrical property of some subatomic particles. It describes how strongly such particles interact through the electromagnetic force. There are two types of charge, which are known as positive and negative charges. Positive charge occurs when there is an excess of protons in a substance or particle. Negative charge results from having more electrons than protons.

The unit of measurement for charge is the Coulomb (C), named after Charles-Augustin de Coulomb. One Coulomb (C) is equivalent to the amount of electric charge carried by approximately 6.24 x 10^18 protons or electrons. The charge of an object can be measured with an instrument called an electrostatic voltmeter or with a device called a Faraday cup.

Conservation of Charge

The principle of conservation of charge states that the total amount of electric charge in a closed system remains constant over time – meaning that it cannot be created or destroyed but only transferred from one body to another. This means that if a group of particles have a total negative charge before a collision between them, then the total negative charge will remain unchanged following the collision, despite any rearrangement of particles caused by the collision.

This principle has been experimentally verified many times and is believed to hold true throughout the universe. In fact, it forms the basis of several fundamental laws of physics – including Maxwell’s equations of electromagnetism, Gauss’ law, and Coulomb’s law.

“The conservation of electric charge is one way to express the universal conservation law” – Leon M. Lederman

To better understand its importance, we can look at examples of charged collisions where charge was conserved. When alpha-particles are shot at gold foil, some scattered backward because of the positively charged nucleus in each atom. This showed that positive charge was concentrated in a tiny region – which led to the discovery of the atomic nucleus.

Another example is when lightning strikes because of a buildup of electrical charge within clouds. The discharge from the cloud neutralizes its own internal electric charge by transferring electricity to the ground below, allowing it to return to a stable equilibrium state with respect to the build-up and distribution of charge.

The conservation of electric charge also helps us understand how various electrical devices work, like batteries, generators, and capacitors. When a battery runs out of power or a generator stops producing it, it simply means there is no more energy available to be extracted by reorganizing charges within the system.

Understanding the concept of “charge” in physics is critical for appreciating how many essential objects function. Charge determines the interactions between subatomic particles and governs both electromagnetic waves and static electric fields. It is one of only four fundamental forces, alongside gravity, weak nuclear force, and strong nuclear force. Knowing that the charge must remain conserved allows physicists to model interactions with more accuracy and make predictions about collisions before they occur.

Frequently Asked Questions

What is a collision?

A collision is an event that occurs when two or more objects come into contact with each other, exchanging energy and momentum. Collisions can be elastic or inelastic, and can result in different outcomes depending on the properties of the objects involved.

What are the types of collisions?

There are two types of collisions: elastic and inelastic. In elastic collisions, the total kinetic energy of the objects is conserved. In inelastic collisions, some kinetic energy is lost and converted into other forms of energy, such as heat or sound.

What is conservation of momentum?

Conservation of momentum is a fundamental principle that states that the total momentum of a closed system remains constant, regardless of any internal changes that may occur. This means that in a collision, the total momentum before and after the collision must be the same.

What is conservation of kinetic energy?

Conservation of kinetic energy is a principle that applies only to elastic collisions. It states that the total kinetic energy of a closed system remains constant before and after the collision. This means that in an elastic collision, the kinetic energy of the objects involved is conserved.

What physical quantities are conserved in elastic collisions?

In an elastic collision, both momentum and kinetic energy are conserved. This means that the total momentum of the system before and after the collision must be the same, as well as the total kinetic energy. This conservation of energy and momentum allows us to predict the outcome of an elastic collision.

What physical quantities are conserved in inelastic collisions?

In an inelastic collision, momentum is conserved but kinetic energy is not. Some kinetic energy is lost and converted into other forms of energy, such as heat or sound. This means that the total momentum of the system before and after the collision must be the same, but the total kinetic energy of the system is not conserved.

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