Deformation in Collisions

A ball hits a thin plate clamped at both ends. The particles in the plate interact through the molecular force curve F(r), so the rebound, the bending and the breaking are all computed step by step. Nothing is pre-animated.

Impact

Ready

Observation

Normal speed

Keys: Space launch / pause, R reset, 123 presets, M switch material

Ball kinetic energy (vs. before impact) 100%
Original bonds broken 0
New bonds formed (new neighbours) 0
Conclusion Choose a material and an impact speed, then launch.

Microscopic view · metal plate

Each dot is one particle (an atom or molecule). Lines show the interaction between neighbouring particles.

Compressed Stretched Beyond rm New bond Broken Clamped
t = 0 Press Launch or the space bar to start.

Molecular force F–r

Each dot is one pair of neighbouring particles: its current separation and force. F > 0 is repulsion, F < 0 is attraction.

Where the energy goes

100% = the ball's kinetic energy before impact.

Key Ideas

1Elastic deformation

Particles move only slightly from the equilibrium spacing r0 and keep the same neighbours. Where the plate is compressed the force is repulsive; where it is stretched the force is attractive. Both point back towards r0. Near r0, F is roughly proportional to Δr, which is Hooke's law at the particle level. Remove the load and the plate recovers: kinetic energy → molecular potential energy → kinetic energy, a nearly elastic collision.

2Plastic deformation

With a larger force, a whole row of particles slides past by one spacing and settles into new equilibrium positions with new neighbours (the green bonds). At every moment some bonds still hold, so the plate does not crack. It cannot go back, so it stays bent, and part of the kinetic energy becomes random vibration of the particles (internal energy). The collision is inelastic.

3Fracture

Somewhere a spacing is pulled past rm, where the attraction is greatest. Beyond rm the attraction gets weaker as the particles separate, so once the load exceeds the maximum attraction there is no equilibrium left and the gap keeps opening. The crack starts on the bottom surface, which is the stretched side: fracture means pulling apart, not crushing.

Metal and glass

Both materials use the same F–r curve. The only difference: in the metal, any two particles that come close attract, so particles can re-bond with new neighbours and the metal can slip and bend. In the glass, a broken bond never re-forms, so there is no plastic stage; it goes straight from elastic deformation to fracture.

About the model

A 2D teaching model of about 370 particles. The F–r curve has the textbook shape; the numbers are illustrative. The ball is rigid, and the particles start at rest (thermal motion is ignored). Real materials contain defects and usually break there first, at forces far below this ideal value.