Trolleys have been used for many years in physics teaching to help understand basic principles such as acceleration, speed, velocity and the effect of friction, gravity and movement. Older versions were made from a wooden block with three wheels attached to the underside. A spring loaded metal rod protruded from one end which acted as both a brake when it came into contact with something and also (when pushed in and locked in place) a propulsion device when it made contact with a wall.
Newer versions may be made from moulded plastic but look and work like the original types.
Trolleys are often rolled down or along ramps where their speed or acceleration can be measured using ticker timers. With some trolleys, removable small bars can sometimes be stuck into fashioned holes in the trolley to accommodate ticker tape, springs or string to facilitate even more uses. Masses can be added to the top of trolleys to increase weight.
Trolleys need to be able to roll smoothly in a straight line. Ensure regular lubrication of the bearings and removal of fluff and sticky tape. Where trolleys may have been dropped or damaged, repairs may need to be completed. Where trolleys are beyond repair, remove wheels and sprung bars to keep as spares.