Balancer and washing machine having the same

A balancer mounted to a drum of a washing machine to offset unbalanced load generated in the drum during rotation of the drum, the balancer comprising:

• a balancer housing having an annular channel defined therein, the balancer housing including a first housing opened at one side thereof and a second housing to cover the first housing to define the annular channel;
• at least one mass movably disposed in the channel;
• and
• at least one magnet coupled to a rear side of the first housing, the rear surface of the first housing being an outer surface of the first housing facing the drum in an axial direction of the drum,
• wherein at least one groove is formed at an inner surface of the first housing to receive the at least one mass at a position corresponding to the at least one magnet whereby the at least one mass is confined to the at least one groove by magnetic force of the at least one magnet when rotational speed of the drum is within a predetermined range,
• wherein the at least one magnet comprises a plurality of magnets arranged in a circumferential direction of the balancer housing,
• wherein each of the plurality of magnets has a pair of N and S poles arranged in an axial direction of the balancer housing,
• wherein the plurality of magnets are disposed in contact with each other such that no gap is present between the respective magnets, and
• wherein each of the plurality of magnets has an inside surface and an outside surface formed in an arc shape.