In a river, large rocks are transported by

slumping
solution
saltation
traction

traction

Traction is a geological process in which a mechanical force transports larger and heavier rocks by sliding and rolling along the substratum. Traction occurs as a water erosion by river water. It results in the movement or transportation of large rocks or stones which are otherwise settled at the bottom, by the force exerted by the water current. These rocks or stones gets displaced from their sites and attains a rolling movement due to fast flowing water current.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.