Ticker timers

This is one of the classic bits of Physics equipment. An electromagnet is connected to alternating current. The electromagnet then turns on and off at 50Hz. It attracts a metal bar down when it is on which applies pressure through carbon paper onto a paper tape. When the electromagnet is turned off, a spring forces the bar back up. Thus a dot is made on the paper 50 times a second. Traditionally the paper is pulled through by a dynamics trolley. The dots get further apart as the trolley goes faster. The analysis is carried out by dividing the tape up into 10 gap lengths, each representing the distance travelled by the tape in 1/5th of a second. These can be stuck end ways on to make a bar graph that is a velocity-time graph for the motion.