A compactor is a machine or mechanism used to reduce the size of material such as waste material or bio mass through compaction. A trash compactor is often used by a home or business to reduce the volume of trash it produces. A baler-wrapper compactor is often used for making compact and wrapped bales in order to improve logistics. Normally powered by hydraulics, compactors take many shapes and sizes. In landfill sites for example, a large tractor (typically a converted front end loader with some variant of a bulldozer blade attached) with spiked steel wheels called a landfill compactor is used to drive over waste deposited by waste collection vehicles (WCVs). WCVs themselves incorporate a compacting mechanism which is used to increase the payload of the vehicle and reduce the number of times it has to empty. This usually takes the form of hydraulically powered sliding plates which sweep out the collection hopper and compress the material into what has already been loaded. Different compactors are used in scrap metal processing, the most familiar being the car crusher. Such devices can be of either the "pancake" type, where a scrap automobile is flattened by a huge descending hydraulically powered plate, or the baling press, where the automobile is compressed from several directions until it resembles a large cube.

In construction, there are three main types of compactor: the plate, the rammer, and the road roller. The roller type compactors are used for compacting crushed rock as the base layer underneath concrete or stone foundations or slabs. The plate compactor, vibrating plate, or tamper, has a large vibrating baseplate and is suited for creating a level grade, while the rammer compactor has a smaller foot. The rammer, or trench rammer, is mainly used to compact the backfill in narrow trenches for water or gas supply pipes etc. Road rollers may also have vibrating rollers. In plates and rollers the vibration is provided by rapidly rotating eccentric masses. In smaller plates the vibration causes a tendency to move forwards, while some larger plates are provided with a directional control. In the rammer the foot is mounted on a sleeve that slides vertically in the leg. Inside the sleeve, a piston is driven up and down by the engine through a reduction gear, crank and connecting rod. Substantial coil springs above and below the piston connect it to the sliding sleeve. The connection between the sleeve and foot is at small angle so that the whole rammer leans away from the operator. The vibrating motion is therefore slightly off the vertical, and this gives the rammer a tendency to 'walk' forwards. The sliding joint in the leg is protected by a flexible bellows.

A ramrod (or scouring stick) is a metal or wooden device used with muzzleloading firearms to push the projectile up against the propellant (mainly blackpowder). The ramrod was used with weapons such as muskets and cannons and was usually held in a notch underneath the barrel. Bullets that did not fit snugly in the barrel were often secured in place by a wad of paper or cloth, but either way, ramming was necessary to place the bullet securely at the rear of the barrel. Ramming was also needed to tamp the powder so that it would explode properly instead of fizzle (this was a leading cause of misfires). The ramrod could also be fitted with tools for various tasks such as cleaning the weapon, or retrieving a stuck bullet. Cap and ball revolvers were loaded a bit like muzzleloaders—powder was poured into each chamber of the cylinder from the muzzle end, and a bullet was then squeezed in. Such handguns usually had a ramming mechanism built into the frame. The user pulled a lever underneath the barrel of the pistol, which pushed a rammer into the aligned chamber.