* Buoyancy: The primary force acting on a balloon is buoyancy, which is the upward force exerted by a fluid (like air) on an object submerged in it. If the balloon is filled with a gas less dense than air (like helium or hot air), the buoyant force will be greater than the weight of the balloon, causing it to rise.

* Wind: The wind will influence the balloon's horizontal velocity, pushing it in the direction the wind is blowing.

* Gravity: While buoyancy pushes the balloon upward, gravity pulls it downward. The net force acting on the balloon is the difference between these two forces.

* Balloon's shape and weight: The shape and weight of the balloon will influence its velocity. A larger, lighter balloon will be more affected by buoyancy and wind.

Other factors that can affect a balloon's velocity:

* Altitude: As the balloon rises, the air density decreases, which can affect the buoyant force.

* Temperature: Hot air is less dense than cold air, so a hot air balloon will rise faster than a balloon filled with cool air.

* Air currents: Balloons can be affected by updrafts (rising currents of air) and downdrafts (descending currents of air).

To determine the precise velocity of a balloon, you'd need to consider all of these factors.