Broomsticks have various magical spells cast on them to help with riding and flying.
References from the canon
- When Harry fell off his Nimbus 2000, it didn't fall to the ground but instead drifted away toward the Whomping Willow, suggesting that it may have had some form of enchantment on it to keep it flying without a rider (PA9).
- Harry's Firebolt, when held and then released, floated at exactly the right height for him to mount it (PA11).
- Early broomsticks had only simple spells placed on them. A model on display in the Museum of Quidditch only moves forward at one speed and will move up, down, and stop (QA1).
Magic Type Charms
From the Web
"Broomsticks" on Harry Potter Wiki