Question

why the metals are expand in summer and contract inwinter

Answer 1

This is coz.....
1)when heated: the molecules in it are moving about more vigorously and so need more room.As a solid is heated the molecules vibrate more violently and the solid expands in all directions.
2)when cooled:the particles contract causing smaller average seperation between them

way to go dude!!
nice question!!!!!

Answer 2

 All materials are made up of atoms. At any temperature above(-273 degrees celsius the atoms will be moving. In a solid they will be vibrating in fixed positions, in a liquid they will be jostling past each other and in a gas they will be whizzing past each other at very high speeds. When a material is heated, the kinetic energy of that material increases and it's atoms and molecules move about more. This means that each atom will take up more space due to it's movement so the material will expand. When it is cold the kinetic energy decreases, so the atoms take up less space and the material contracts.