1)This type of reaction is called thermal decomposition . Copper carbonate is green and copper oxide is black. You can see a colour change from green to black during the reaction. The carbon dioxide produced can be detected using limewater, which turns milky. 2) The extremely low pressure of the partial vacuum inside the can made it possible for the pressure of the air outside the can to crush it. A can is crushed when the pressure outside is greater than the pressure inside, and the pressure difference is greater than the can is able to withstand.
As the amplitude of pendulum motion increases, the period lengthens, because the restoring force −mgsinθ increases more slowly than −mgθ (sinθ≅θ−θ3/3!for small angles).
