Forces acting on a basketball in flight

There are four main forces acting upon a basketball in flight:
Gravity, Drag force, Magnus force, and Buoyant force.

Gravity:Gravity ball

The most dominant force acting on a basketball in flight is gravity. It is a force that acts always vertically on the basketball, as the Earth pulls it straight down.

Drag force:drag ball

The drag force is also called air resistance or friction. This force acts on the basketball when it moves through the air, as the ball pushes through the air molecules. It opposes the basketball’s movement. The drag force depends on density of the air –as more molecules offer more resistance–, contact area, and velocity of the ball.

Magnus force:Magnus ball

This is an interesting force to discuss. The Magnus force is caused by the translational velocity and the spin of the ball. It is the force responsible for a baseball to curve and for a football player to be able to curve corner kicks. If the basketball moves horizontally forward through the air with backspin, the Magnus Force acts upward on it.

Buoyant force:Buoy ball

This force acts upwards on the basketball. This is the force that explains the floating of boats and ice-cubes. It doesn’t matter if the ball is moving or not. It is caused by the pressure difference (however small) on the top and bottom of the ball; that is, by the collisions of air molecules on its outside surface.

The four forces that act on a basketball in flight are shown in black. Notice that the Gravity and the Buoyant force are always vertical. The Drag force is always opposing the ball's translational velocity. The Magnus force depends on the translational velocity and the spin.

The four forces that act on a basketball in flight are shown in black. The translational velocity and the spin (rotational velocity) are shown in blue.

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