PHYSICS
Airborne for under a second
Time in the air depends only on how high you rise. A 1 metre leap gives about 0.9 seconds, and nothing you do mid-air changes the path your body has started on.
Time a jumpA dunk is a short trip against gravity.
The ring is 10 feet off the floor, and once your feet leave it your path is already set. Here is what the numbers say about the jump, the hang time and the nine seasons college basketball said no.
- Height is set at take-off
- Most of the float is near the top
- Landing is part of the jump
- Simple physics, big moment
THE SHORT ANSWER
Gravity wins,
but not straight away.
A dunk is physics, rules and practice.
Each card takes one of them.
HISTORY
Nine seasons without a dunk
US college basketball banned the dunk before the 1967-68 season, citing injuries and broken equipment, and only allowed it back before 1976-77.
Read the history
TRAINING
Small gains, landed well
A review of 26 studies found jump training added about 8.7% to a countermovement jump in healthy people. Learning to land is part of it.
Training notes
IF YOU WANT TO JUMP HIGHER
Train the jump,
and the landing.
These are general notes from the sources below, not a training plan. If you have not exercised for some time, or have a medical condition, the NHS says to speak to your GP first.
Measure it the simple way
Mark your standing reach on a wall, then jump and touch as high as you can. The difference is your vertical leap.
Use the dip and the arms
A quick knee bend before take-off added about 12% to jump height, and a strong arm swing about 10% more.
Build strength first
The NHS advises strengthening activities for all major muscle groups, legs and hips included, on at least 2 days a week.
Practise landing softly
A coach quoted by Popular Science stresses landing with the impact spread through ankles, knees and hips: your body only jumps as high as it trusts itself to land.
TWO NUMBERS WORTH KNOWING
Why the ban,
and what training adds.
One figure from the 1967 rule change,
one from a review of jump-training trials.
1,500+ injuries
Injuries around the backboard in 1967
When the NCAA rules committee banned the dunk, it cited injury concerns first: more than 1,500 injuries around the backboard in 1967. Shattered backboards and bent rims were the other reason.
THE 1967 BAN · NCAA NEWS
≈ 8.7%
Gain in countermovement jump height
A meta-analysis of 26 studies in the British Journal of Sports Medicine found plyometric training raised countermovement jump height by 8.7% on average in healthy people (95% CI 7.0 to 10.4%).
JUMP TRAINING · BJSM 2007
The same review found smaller average gains for a squat jump and a drop jump (4.7% each) and 7.5% for a countermovement jump with arm swing.
HOW LONG IN THE AIR?
Pick a leap,
see the hang time.
Choose how high the jump lifts your body. The value is the total time from take-off to landing, worked out from the standard jump formula. The bar shows how long that is.
Calculated with h = g × t² / 8 and g = 9.81 m/s². Rounded to two decimal places.
THE YEARS WITHOUT A DUNK
Banned in 1967,
back in 1976.
The NCAA rules committee outlawed the dunk before the 1967-68 season. Its report cited injuries first, and backboards were being shattered and rims bent, with some games cancelled because the basket could not be replaced.
Scoring did not suffer: average field goals made in Division I men's games rose during the ban. The dunk returned to games before the 1976-77 season, though not yet in pre-game warm-ups, where officials could give a technical foul.
In conversation
Questions people ask
How high is a basketball ring?
The top edge of the ring is 10 feet (3.05 m) above the floor, the same under NBA and international rules. The NBA rulebook also sets an 18-inch inside diameter for the ring.
Can anyone stay in the air for more than a second?
It would take a rise of about 1.2 metres or more. It has been suggested people cannot pass one second of hang time, but Popular Science notes there is no hard science proving a limit.
Can a player hang or glide in mid-air?
No. The path of your centre of gravity is fixed the moment you leave the floor. Moving arms and legs can shift where your hands are, which is how players appear to reach further.
Why does hang time look longer than it is?
You move slowest near the top of a jump. Because height grows with the square of time, half of your time in the air is spent in the top quarter of the jump.
Does jump training actually work?
A 2007 meta-analysis of 26 studies found plyometric training improved vertical jump height in healthy people, by 4.7% to 8.7% on average depending on the type of jump.
Sources
Each figure on this page comes from the sources below.
- NBA Official Rulebook, Rule No. 1: Court dimensions and equipment
- NCAA News archive (2007): Chronicle of the jam, the dunk outlawed and restored
- Markovic G. Does plyometric training improve vertical jump height? A meta-analytical review. Br J Sports Med 2007
- Popular Science: The physics behind iconic NBA slam dunks
- Wikipedia: Vertical jump (measurement and the hang time formula)
- NHS: Physical activity guidelines for adults aged 19 to 64