Something accelerates in the direction opposite to its motion when a force acts on it in the opposite direction of its velocity. This is known as deceleration or negative acceleration.

Here are some common scenarios:

* Friction: Friction always acts opposite to the direction of motion, causing an object to slow down. For example, a car slowing down because of friction from the brakes.

* Gravity: When an object is thrown upwards, gravity acts downwards, causing it to decelerate until it momentarily stops before falling back down.

* Air resistance: Air resistance acts opposite to the direction of motion of an object moving through the air, causing it to slow down. For example, a parachute slows down a skydiver.

* Springs: When a compressed or stretched spring is released, it exerts a force opposite to the direction of the object's motion, causing it to decelerate.

* Braking: When you apply brakes to a vehicle, the force applied by the brakes acts opposite to the direction of motion, causing it to slow down.

In essence, any force that acts in the opposite direction of an object's velocity will cause it to accelerate in the opposite direction of its motion (decelerate).