Michelle Obama is looking for at least 20,425 people to help her break a Guinness World Record next week. The first lady will lead hundreds of children doing a minute of jumping jacks on the White House's South Lawn on Tuesday, kicking off a 24-hour challenge, AP reports. Groups around the country will join the effort to beat the record for the most people doing jumping jacks in a 24-hour period. Event organizer National Geographic has more details. (More Michelle Obama stories.)