Difference Between Elastic and Inelastic Collision with Examples
A collision in physics is a short-duration event when two or more bodies come into contact and exert forces on each other. The study of collisions is crucial for mastering JEE Main concepts like conservation of momentum and energy transfer. These interactions can be observed in simple experiments, sports, vehicle accidents, or at the atomic scale. Understanding different types of collision scenarios helps decode numerous exam questions and real-world applications.
The word "collision" also appears in various mechanical and statistical contexts in JEE, such as particle collisions in kinetic theory or impulse-momentum interactions. This topic supports many related areas, including momentum and conservation of momentum. For deeper mastery, refer to Vedantu’s expert-written guides that thoroughly align with the JEE Main and NCERT learning paths.
Collision: Definition and Meaning in Physics
In physics, a collision is defined as an event where two or more bodies interact over a very short time, usually resulting in a rapid exchange of momentum and possibly energy. Though typically associated with objects touching, collisions can also occur without direct contact—such as between charged particles—through fundamental forces. The key factor is the interaction causing a significant change in their motion.
Common real-life examples include a bat striking a ball, two cars crashing, and gas molecules bouncing inside a container. Each scenario demonstrates core principles tested in JEE Main exams.
Types of Collision: Elastic, Inelastic, and Perfectly Inelastic
There are several distinct types of collision important in exams and problem-solving. Recognizing these categories helps in applying the correct formulas and logic when momentum and energy conservation rules differ.
| Type | Momentum Conserved? | Kinetic Energy Conserved? | Exam Example |
|---|---|---|---|
| Elastic | Yes | Yes | Gas molecule collisions |
| Inelastic | Yes | No | Car crashes, clay balls |
| Perfectly Inelastic | Yes | No | Two objects stick together |
An elastic collision conserves both kinetic energy and momentum. In an inelastic collision, momentum is conserved, but some kinetic energy turns into heat, sound, or deformation. A perfectly inelastic collision is a special case where objects stick and move as one after impact—common in exam questions on "maximum loss of kinetic energy". To distinguish, recall that only elastic collisions allow both bodies to rebound with no energy loss.
For more on the differences, visit the elastic collisions in one dimension and coefficient of restitution resources.
Laws and Formulas Governing Collision
Solving collision problems relies on key principles. Memorize the main laws and how to apply them under exam conditions.
- Law of Conservation of Momentum: Total momentum before collision equals total momentum after, provided no external force acts. Key for all collision types.
- Kinetic Energy Conservation: Applies only in elastic collisions. For inelastic types, only momentum holds.
- Coefficient of Restitution (e): e = (Relative speed after)/(Relative speed before); indicates how 'bouncy' the collision is.
| Symbol | Meaning | SI Unit |
|---|---|---|
| m | Mass of body | kg |
| u | Initial velocity | m/s |
| v | Final velocity | m/s |
| e | Coefficient of restitution | (unitless) |
Use these key formulas for calculations:
- Total momentum before: m1u1 + m2u2
- Total momentum after: m1v1 + m2v2
- Elastic collision velocities (1D): v1 = [(m1 - m2)/(m1 + m2)]u1 + [2m2/(m1 + m2)]u2
- Perfectly inelastic, common velocity: V = (m1u1 + m2u2)/(m1 + m2)
Review the conservation of momentum and laws of motion pages for derivations and concept deep-dives.
Numerical Example and Common Pitfalls in Collision
Let’s solve a classic JEE Main problem involving collision and apply these formulas.
- Two blocks (m1 = 2 kg, u1 = 5 m/s and m2 = 3 kg, u2 = -2 m/s) collide elastically in one dimension. Find final velocities.
- Conservation of momentum: 2×5 + 3×(-2) = 2v1 + 3v2
- Conservation of kinetic energy: (since elastic)
- Substitute into formulas for v1 and v2:
- v1 = [(2-3)/(2+3)]×5 + [2×3/(2+3)]×(-2) = -1×5/5 + 6×(-2)/5 = -1 + (-2.4) = -3.4 m/s
- v2 = [2×2/(2+3)]×5 + [(3-2)/(2+3)]×(-2) = 4×5/5 + 1×(-2)/5 = 4 + (-0.4) = 3.6 m/s
Final velocities: v1 = -3.4 m/s, v2 = 3.6 m/s.
Common errors include forgetting to use proper signs for velocities or wrongly assuming kinetic energy is conserved in all cases. Carefully differentiate between elastic and inelastic collision while applying laws.
Test yourself using problems from the problems on collisions with solutions and kinematics practice papers.
Real-Life Applications and Revision Points for Collision
The concept of collision appears throughout physics, not just in car crashes. Examples for JEE Main include atomic nuclei scattering, collisions in particle accelerators, ball games, and even spacecraft docking procedures.
- Gas molecules exchanging energy (elastic, as in kinetic theory of gases)
- Billiard balls rebounding (near-elastic)
- Bullet embedding in wood (perfectly inelastic)
- Rocket stages ejecting (momentum conservation)
- Ball hits ground and bounces (analyzed via coefficient of restitution)
Key revision points for exams:
- Always check if both momentum and energy are conserved.
- Use the center of mass frame for simplified calculations in some problems (see centre of mass).
- Remember: Sign convention is critical for velocities.
- Coefficient of restitution tells you “how elastic” the collision is.
- Practice with real exam-style numericals from mock tests.
For formula recaps and last-minute prep, consult work energy and power revision notes and laws of motion revision notes.
Mastering collision enables you to solve a wide range of JEE Main questions about momentum, energy, or event timing. Vedantu’s stepwise guides are structured to demystify tricky concepts and enhance performance, ensuring concept clarity and success in the exam.
FAQs on Collision: Meaning, Types & Examples in Physics
1. What is a collision in physics?
A collision in physics is an event where two or more bodies come into contact and exert forces on each other for a brief period, causing changes in momentum and energy.
Key points:
- It involves momentum transfer and possible kinetic energy change.
- Can be elastic, inelastic, or perfectly inelastic.
- Common in car crashes, billiards, sports, and microscopic particle interactions.
2. What are the types of collisions?
Collisions are mainly classified based on conservation of kinetic energy and momentum.
Major types:
- Elastic collision: Both momentum and kinetic energy are conserved (e.g., two billiard balls).
- Inelastic collision: Momentum conserved, but kinetic energy is lost (e.g., car crash with damage).
- Perfectly inelastic collision: Objects stick together after collision, maximum kinetic energy lost (e.g., clay balls sticking together).
3. What is the difference between elastic and inelastic collisions?
The main difference lies in energy conservation:
- Elastic collision: Both momentum and kinetic energy remain the same before and after collision.
- Inelastic collision: Momentum is conserved, but kinetic energy decreases as some is transformed into heat, sound, or deformation.
Examples: Bouncing rubber balls (elastic), car accidents with dents (inelastic).
4. How is momentum conserved in a collision?
Momentum remains conserved in all types of collisions, as stated by the Law of Conservation of Momentum, provided there are no external forces.
Key steps:
- Total momentum before = total momentum after the collision.
- Apply the formula: m1u1 + m2u2 = m1v1 + m2v2 (for two bodies).
- Works for one-dimensional (head-on) and two-dimensional collisions.
5. Can kinetic energy be lost in a collision?
Yes, kinetic energy can be lost during collisions, particularly in inelastic and perfectly inelastic types.
Lost energy is often transformed into:
- Heat
- Sound
- Deformation of objects
6. Where do collisions occur in real life?
Collisions are common in daily life as well as natural and scientific phenomena.
Examples include:
- Car accidents
- Billiard/snooker balls
- Sports (cricket ball hitting the bat)
- Molecular collisions in gases
- Astronomical bodies colliding (meteors, asteroids)
7. What is the law of conservation of momentum and how does it apply to collisions?
The Law of Conservation of Momentum states that within a closed system with no external forces, the total momentum remains constant during a collision.
Application in collisions:
- Calculate total momentum before and after the event using m x v (mass × velocity).
- Set initial and final momentum equal to solve for unknowns.
8. Can two bodies collide without physically touching?
Yes, collisions can occur without direct contact if the objects interact through forces, such as electrical or magnetic fields.
Examples:
- Electrons deflecting each other via electrostatic repulsion
- Magnetic spheres repelling each other
9. What happens to internal energy during a collision?
During inelastic collisions, some kinetic energy is converted into internal energy (like heat, deformation, or sound).
Bullet points:
- In perfectly elastic collisions: Internal energy doesn't change.
- In inelastic/perfectly inelastic collisions: Internal energy increases due to loss of kinetic energy.
10. Are all collisions perfectly elastic or inelastic in real life?
Most real-life collisions are partially inelastic, with some kinetic energy lost.
Key points:
- Only idealized situations (like atomic gas molecules) are perfectly elastic.
- Everyday occurrences (car crashes, football kicks) are usually inelastic.
11. What is the difference between a head-on collision and an oblique collision?
Head-on collision occurs when bodies move along the same line (1D), while oblique collision involves different angles and possibly two dimensions (2D).
Key points:
- Head-on: Simpler mathematics, momentum/energy along one axis.
- Oblique: Need to resolve velocity and momentum into components.
