Does a ball roll right from the start?
Moving and spinning are different motions. Use whether the bottom of the ball slides to tell center, top and bottom hits apart.
One thing to remember today
A ball can slide even while it spins. Natural roll is the state in which the bottom of the ball does not slide on the cloth.
Written and edited by TTBoys · How we write and check sources · Report an error
Reading the motion in diagrams
① Just after a center hit
② Sliding while spinning up
③ Natural roll
A concept diagram made by TTBoys for learning. It is not a measured graph or simulation result from a paper; arrow lengths and angles are there to explain the principle.
The hit sets both motion and spin
An ideal center hit with a nearly level cue starts the ball moving with almost no forward or backward spin at first. A top or bottom hit also creates forward or backward spin right after impact. Not every shot starts without spin.
Once the tip leaves the ball, the cue no longer pushes it. Friction between the cloth and the ball then changes its speed and spin. The saying “the spin kicks in later” does not mean spin switches on later; it can describe the process of the ball’s motion changing.
Compare the speed of the bottom of the ball
For straight motion with no sidespin and no jump, let v be the forward speed, R the ball radius and ω the angular speed of forward spin. The sliding speed at the bottom is u = v − Rω. In this formula forward spin is positive.
When u is 0, the ball is in natural roll. When u is positive, the bottom of the ball slides forward and friction acts backward. With too much forward spin, u is negative and friction can act in the opposite direction. Friction always acts to reduce the relative sliding at the contact point, not simply against the motion of the ball’s center.
A bottom hit can still roll forward later
A bottom (draw) shot that travels far enough without meeting an object ball or a cushion can change from backspin → no forward or backward spin → forward spin → natural roll. When each change happens depends on the launch speed and spin and on the cloth.
Reaching natural roll does not mean the ball keeps the same speed forever. Rolling resistance, from things like the cloth deforming, slows it down. Do not describe sliding friction and rolling resistance as the same thing.
An observation drill suggested by TTBoys
Watch the same center hit up close
- Place one ball in the same spot and hit it 5 times at a comfortable speed with no sidespin. Use a dot or logo already on the ball, and do not stick tape or anything else on its surface.
- Fix the camera where the moving ball cannot hit it. Film so that both the distance traveled and the spin marker are visible.
- Watch the change in center position frame by frame and the rotation of the marker separately. When you compare tip positions or speeds, change only one at a time.
What to watch: Compare the stretch where the ball moves forward while the marker barely turns with the stretch after spin has built up.
When interpreting: If you cannot see a spin marker, do not conclude zero spin or natural roll from position video alone. This exercise is for observation; it is not an experiment that measures a friction coefficient.
Connect to Basics, Systems and Practice
Evidence from papers and where it applies
Sources reviewed: 2026-10-10 · The explanations and drills are TTBoys' editing.
Experimental and theoretical paper · S. Mathavan · M. R. Jackson · R. M. Parkin
Application of high-speed imaging to determine the dynamics of billiards ↗
American Journal of Physics 77, 788–794 (2009) · DOI 10.1119/1.3157159
What this source explains: Tracks changes in position and velocity in high-speed video to study sliding and rolling, cushion impacts and separation angles.
Limits: The experiments used a snooker table and calibrated camera equipment. This does not mean a smartphone gives the same accuracy, and tracking spin needs separate observation.
Educational material · David Alciatore (Dr. Dave)
Pool Ball Slide and Roll With Sidespin ↗
Online explanations and demonstrations
What this source explains: Explains the difference between sliding and rolling, and rolling with sidespin.
Limits: This is teaching material, kept separate from peer-reviewed papers. Read it by whether the contact point slides, not by players’ everyday terms.
Theoretical paper · 김형찬 (Hyeong-Chan Kim)
Motions of a Billiard ball After a cue Stroke ↗
New Physics: Sae Mulli 72, 208–223 (2022) · DOI 10.3938/NPSM.72.208
What this source explains: Analyzes the launch speed, spin and squirt of the ball, taking into account the cue–ball impact and the flexibility of the cue.
Limits: This is a study of a cue impact model. It is not an experiment that proves a particular named stroke is better or that every real shot succeeds.