Collisions are a fundamental concept in Physics that help explain how objects interact when they collide, such as in car crashes, sports, and even subatomic particle interactions. Understanding collisions is important for JEE, NEET, and other competitive exams, as well as for real-world applications in engineering and safety design.
In this blog, we answer the most frequently asked questions (FAQs) on Collisions to give you a clear understanding of this crucial topic.
A collision in physics refers to an event where two or more objects come into contact with each other, typically with a large force, over a short time period. Collisions involve the exchange of energy and momentum between the colliding bodies.
The two main types of collisions are:
The law of conservation of momentum states that the total momentum of a system of interacting particles remains constant, provided no external force acts on the system.
This principle holds true in both elastic and inelastic collisions, but kinetic energy is only conserved in elastic collisions.
Here are the key differences between elastic and inelastic collisions:
| Property | Elastic Collision | Inelastic Collision |
|---|---|---|
| Kinetic Energy | Conserved (no loss of energy) | Not conserved (some energy is lost to heat, sound, etc.) |
| Momentum | Conserved in all types of collisions | Conserved in all types of collisions |
| Deformation | No permanent deformation of objects | Objects may be deformed or broken |
| Example | Collisions between hard balls (e.g., billiard balls) | Car crashes or objects colliding and bouncing apart |
The velocity of objects after a collision depends on the type of collision and the initial velocities of the objects. You can use the conservation of momentum to calculate the velocities after the collision.
The coefficient of restitution (e) is a measure of how elastic a collision is. It is the ratio of the relative speed after collision to the relative speed before collision.
Formula:
e=vrelative aftervrelative beforee = \frac{v_{\text{relative after}}}{v_{\text{relative before}}}e=vrelative beforevrelative after
Where:
In any collision, kinetic energy may be transferred between the colliding objects or converted into other forms of energy (like heat, sound, or light).
The total energy (including both kinetic and other forms) is conserved, but the specific form of energy may change.
A completely inelastic collision is one in which the colliding objects stick together after the collision and move as a single object. This type of collision maximizes the loss of kinetic energy, although momentum is still conserved.
Collisions are critical to many practical applications in real life, such as:
To prepare for collisions in exams like JEE or NEET, follow these tips:
Collisions are a fascinating and crucial part of Physics that help explain a wide range of phenomena. Whether it's understanding the transfer of energy, momentum conservation, or predicting the outcome of physical interactions, mastering collisions is essential for both academic exams like JEE and NEET, as well as for real-world problem-solving. By understanding the various types of collisions and practicing key problems, you can easily excel in this topic.
A fully elastic collision means no kinetic energy is lost during contact. In actuality, each macroscopic collision between objects will convert some kinetic energy to internal energy and other energy sources. Hence no large-scale collision is completely elastic. On the other hand, some issues are close enough to be fully elastic to be approximated as such. In this scenario, the restitution coefficient is one.
An inelastic collision is one in which part of the kinetic energy is changed to some other form of energy in the collision. In inelastic collisions, momentum is maintained (as in elastic collisions). Still, kinetic energy cannot be tracked throughout the collision because part of it is transformed into other kinds of energy. The coefficient of restitution is not one in this scenario.
The force acting between the interacting entities is inversely proportional to the collision time. The collision time must be minimized to optimize the force between two bodies. The same might be said for the other situation. The collision duration must be increased to reduce the force between two bodies. The principles may be seen in the notion of installing airbags in automobiles. The goal is to give the objects more time to collapse to reduce the impact on them during a collision. Airbags in automobiles do this by lengthening the time it takes to stop the vehicle's velocity for both the passenger and the driver.
A two-dimensional collision follows the same laws as a one-dimensional collision: total momentum in each direction is constant before and after the impact. Before and after an elastic contact, the total kinetic energy is the same.