Work is done when a force acts on an object AND the object moves in the direction of the force.
-- Pulling a trailer up a hill. YES. The trailer is moving in the direction of the pulling force.
-- Carrying a box down a corridor. No. The box is not moving in the direction of gravity (down) OR in the direction of your arm (down the corridor).
-- Suspending a heavy weight with a strong chain, No. There's a force (gravity) acting on the weight, but the weight is not moving at all.
-- Pushing against a locked door. No. There's a force (your muscles) acting on the door, but he door is not moving at all.
