Answer:-A metal ball is made up of atoms having minimum interatomic distance, so when we heat the metal its atoms actually vibrate about their mean position and thus colliding with neighboring atoms and making them to vibrate, due to this continuation process metals size increases or metal expands on heating.
When heat is added to a substance, the molecules and atoms vibrate faster. As atoms vibrate faster, the space between atoms increases. The motion and spacing of the particles determines the state of matter of the substance. The end result of increased molecular motion is that the object expands and takes up more space “Steel will expand from 0.06 percent to 0.07 percent in length for each 100oF rise in temperature. The expansion rate increases as the temperature rises. Heated to 1,000oF, a steel member will expand 9½ inches over 100 feet of length When a metal ring is heated both inner and outer radii increase. This can be understood better by visualizing that the ring in reality is a rod bent into a circle. That rod will expand upon heating. The same bar bent into a ring thus also expands.