The special case of inelastic collision is known as a perfectly inelastic collision. Here, after collision two objects stick together. Refer to the figure above. Example: when wet mudball is thrown against a wall, the mudball sticks to the wall.

An inelastic collision is one in which objects stick together after impact, and kinetic energy is not conserved. This lack of conservation means that the forces between colliding objects may convert kinetic energy to other forms of energy, such as potential energy or thermal energy.

A collision in which the objects stick together is sometimes called perfectly inelastic because it reduces internal kinetic energy more than does any other type of inelastic collision. Sports science and technologies also use physics concepts such as momentum and rotational motion and vibrations.

An elastic collision can be defined as a state where there is no net loss in kinetic energy in the system as the result of the collision. An inelastic collision can be defined as a type of collision where this is a loss of kinetic energy.

In an inelastic collision of two bodies, the total energy of the system changes to some other form but the linear momentum and kinetic energy remain unchanged.

The velocity of the system’s center of mass does not change, as long as the system is closed. The system moves as if all the mass is concentrated at a single point. However, the center of mass itself does not rotate; instead it will make a parabolic path, as if it was a point particle.

Since these are inelastic collisions, the kinetic energy is not conserved, but total energy is always conserved, so the kinetic energy “lost” in the collision has to convert into some other form, such as heat, sound, etc. In the first example where only one car is moving, the energy released during the collision is K.

Again, after using the car crash calculator, you can obtain the average impact force of about 2.5 kN that is almost 25 times smaller than without the seat belt. It corresponds to the weight of 1.24 tons.