It is important for you to be able to predict the path or the trajectory of the pickleball so that you can better orient your racquet or position yourself on the court to return the ball in the direction you intend.
The field of Kinematics addresses various aspects of pickleball motion such as velocity, acceleration, displacement, and time, without considering impact forces with the paddle or the ground, or aerodynamic effects, which are addressed in several different articles.
Forces on a Pickleball
Forces that act on a pickleball originate from several different sources. For now, let’s focus on how the pickleball travels through the air after it strikes the paddle and before it hits the ground. For simplicity, we will consider that the pickleball is constrained to motion in the X-Y plane of the paper. Figure 1 depicts what is known as the “free body diagram”, or FBD of the pickleball, showing all of the forces acting on the pickleball as it travels through the air.
The impact of the paddle propels the ball at a velocity (v) in a direction (θ) measured with respect to the horizontal (X) axis. As the ball travels through the air, it may be subjected to the following forces:
- FGravity is the gravity force, which is always in the negative Y-axis (vertical). Gravity is a restoring force that always acts to bring the ball to the ground. It is always present and is constant.
- FDrag is the drag force, which is always opposite the direction of travel (negative v-direction). It is always acting to slow the ball down in the horizontal axis, and if the ball is rising, it pushes the ball downwards, but if the ball is falling, it tries to keep the ball afloat. The magnitude of the drag force is dependent on numerous factors (which we will discuss in a future article), but it is always present as long as the ball has a velocity.
- FWind is the wind force, which may or may not be present. It is a special case of the drag force, and depending on its direction and velocity, it may increase or decrease the horizontal velocity of the ball, push the ball upwards or downwards, or it may cause the ball to change direction during flight.
- FLift is the lift force, which may or may not be present, and can be upward or downward depending on the amount and direction of the spin velocity (ω) on the ball. As we will later see in future articles, spin has a significant effect on the trajectory of the ball.
Forces You Can Control
It should be apparent that pickleball players cannot really control how gravity and aerodynamic drag affect the path and speed of the ball, and that they must learn to adapt to wind conditions as they occur. The only means by which a pickleball player can control the ball trajectory is by controlling the initial velocity, its direction, and amount of spin (or lift) they can impart to the ball. We discuss the aerodynamics of spin in “Can Topspin Enable a Faster Serve?“
The initial velocity is dependent on the amount of velocity pickleball players can apply to the ball when they strike it. The direction of the ball is determined by how the player orients the paddle while striking the ball. The amount of lift (positive or negative) a player can put on the ball depends on how much spin the player can apply to the ball. Controlling the velocity, direction, and spin of the ball requires an understanding of “what” needs to be done (knowledge) before determining “how” it should be accomplished (technique).
Our discussion in the Pickleball Dynamics series of articles concerns learning how the ball travels after the player has hit the ball and before it lands on the ground. Understanding the kinematics of the pickleball will allow you to better place the ball in the location that you intend, and it will allow you to better position yourself and your paddle to receive and return the ball.
What's Next?
In our next article, “Pickleball Equations of Motion“, we will develop a mathematical model based on projectile equations of motion that shows how the force of gravity (FGravity) alone affects the trajectory the pickleball. In another article, “How Fast is a Pickleball Serve?“, we will apply this mathematical model to predict the theoretical fastest pickleball serve. In “How Does Aerodynamic Drag Affect a Pickleball?“, we will add complexity to the model by evaluating how aerodynamic drag (FDrag), wind forces (FWind), and spin (FLift) affect the motion of a pickleball during serves, groundstrokes, volleys, and dinks.
