Comment on the following statements: (a) sponge though compressible is a solid? (b) Can a rubber band change its shape on stretching?
Hint: Because of the presence of the air cavities inside the sponge is compressible being a solid. The sponge has numerous pores in it which can be referred to as air cavities, in which air is trapped and on compressing the sponge it comes out. We all know that sponge is a porous material. Here we have asked about Can a rubber band change its shape on stretching? For a given problem the rubber band is stretched to some distance; some magnitude of the force is applied. The mathematical relations for restoring the force are integrated to calculate the work against the restoring force.
Complete step-by-step solution: (a) Though even though they are originally made from the natural sea sponges, they are generally made from the synthetic materials generally. With the help of the polyurethane, polyester and vegetal cellulose, synthetic sponges are made up of. As we are aware, the most well known property of solid is that it has definite shape and mass. The main reason why the sponges can easily soak into the liquid is the pores present in it . Air can get trapped inside these holes when there are holes in the sponge. Therefore, a sponge can be considered as solid though it is compressive. (b) A rubber band is considered a solid because it changes the shape under the action of force and when the force is removed, it regains its original shape. Stretching a rubber band is a reversible change.
Note: It must be noted that compressibility is the measure of how much of a given volume of matter reduces when placed under pressure. Because of its porous nature and air cavities the sponge is an exception. As we have seen , a sponge remains its shape and mass remains the same after the compression. Since the size of the rubber band changes, the stretching of the rubber band is a physical change . When the rubber band stretches the colour of the band also changes. However, the material that the rubber is made up of does not change.