6b Heating Rubber
Theory: Rubber - elasticity driven by entropy
Rubber is entropy-elastic that means its elasticity is driven by entropy. Entropy is a measure for disorder and increases with increasing temperature.
Rubber consists of long chain molecules that form a network. In its relaxed form a rubber band is in a highly disordered internal state. Upon stretching the long chain molecule of the rubber band are aligned and the disorder decreases. What will happen if a stretched rubber band is heated?
What you need:
Rubber band, cut open
empty plastic bottle or glas bottle with lid
water
hair dryer
door handle/window handle
What do you have to do?
1 Cut a rubberband to obtain a straight piece of rubber and tie a loop at one end
2 Fill a plastic bottle/plastic beaker with tap water and clamp the open end of the rubber band under the lid
3 Slide the rubber loop around a door handle, the water filled bottle/beaker should stretch the rubber band without rupturing.
HINT: If necessary, adjust the water level in the bottle/beaker to stretch the rubber band under its weight
4 Place a removable mark at the wall/door to see where the top of the bottle is with the stretched rubber band.
5 Plug in a hairdryer, turn it on and heat the rubber band by moving the dryer up and down the rubber band.
What do you observe? Does the rubber band get (1) longer/ (2) shorter? Type the number of the correct answer into the box below.