A refrigerator is a heat engine which works in opposite to other heat engines like petrol engine and diesel engine. Thus, a refrigerator extracts heat from the freezing chamber, some work is done on it by electric motor and rejects heat into the surrounding air, thus warming the air. Therefore if the door of a running refrigerator is left open, the room will not be cooled down but instead heated slightly.
Initially, the ball is moving with a certain velocity and the player has to apply a retarding force to bring the ball to rest in his hand. As change in momentum dP = F × dt, if he abruptly catches the ball; i.e. dt is small, then he will have to apply a large retarding force due to which he gets hurt. If he lowers his hands, he would have to apply the smaller force for longer time to bring the ball to rest. Hence he would not get hurt.
The detailed step by step description of a chemical reaction is called reaction mechanism.
Substrate + reagent -> intermediate -> product
*Substrate:- The reactant molecule which is attacked by any reagent.
*Reagent:- The attacking species eg. Electrophiles, Nucleophiles, Free Radicals, etc.
Engineering