When an object slows down, its acceleration is negative (in a linear sense), or in a direction opposed to its motion (in a vector sense).
it changes direction,it speeds up or slows down
When an object slows down it is still accelerating.
gravity
an object can accelerate both up and down
Because that's the definition of "accelerate". "Accelerate" doesn't mean "speed up", although that's how everybody who rides in a car uses the word. "Accelerate" means "change the speed or the direction of motion, or both".
Velocity can change due to a change in speed or direction of an object. It can also change if there is a force acting on the object, causing it to accelerate or decelerate. In simpler terms, velocity changes when an object speeds up, slows down, or changes direction.
It slows the object down.
Gravity is the force that causes objects to fall, while air resistance or drag slows down a falling object as it moves through the air. The larger the surface area of the object, the greater the air resistance force, which opposes the force of gravity and slows the object down.
Retardation or negative acceleration or deceleration.
Slower than it was before.
When a car slows down
Yes, an object's momentum changes when it slows down. Momentum is calculated as the product of an object's mass and velocity, so any change in velocity, such as slowing down, will result in a change in momentum.