When the average kinetic energy of the molecules goes up (a rise in temperature), the average speed of the molecules increases. And lower average kinetic energy of the molecules means they have lower speed. However, a change in average kinetic energy is not directly proportional to a change in average speed. 1.
An appreciation means an increase in the value of a currency. It means a currency is worth more in terms of foreign currency.
, recognize, understand - The use of appreciate should involve valuing something or understanding it sympathetically; when there is no value or sympathy, use recognize or understand; appreciate first meant set at a price; appraised..