Galileo's Law of Odd Numbers
The distances traversed during equal time intervals in free fall
| Time Interval (τ) | Position (y) | Position in y₀ units | Distance in Interval | Ratio |
|---|
Example
Question:
Galileo's law of odd numbers: "The distances traversed, during equal intervals of time, by a body falling from rest, stand to one another in the same ratio as the odd numbers beginning with unity [namely, 1 : 3 : 5 : 7 ...]." Prove it.
Solution:
Let us divide the time of free-fall into many equal intervals \(\tau\) and find the distances traversed during successive intervals. Since initial velocity is zero, \[ y = -\frac{1}{2}gt^2 \] Using this equation, we can calculate the position of the object after different time intervals: \(0, \tau, 2\tau, 3\tau, ...\). If we denote \(-\frac{1}{2}g\tau^2\) as \(y_0\) (the distance fallen in the first interval \(\tau\)), then:
- Position after \(n\)th interval: \(y(n\tau) = -\frac{1}{2}g(n\tau)^2 = -\frac{1}{2}g n^2 \tau^2 = n^2 y_0\)
- Distance traversed in \(n\)th interval: \(s_n = y(n\tau) - y((n-1)\tau) = n^2 y_0 - (n-1)^2 y_0 = (2n-1) y_0\)
Physics Explanation:
Galileo's law of odd numbers states that the distances traversed during equal time intervals by a body falling from rest stand to one another in the ratio of odd numbers beginning with unity (1:3:5:7...).
The position of a freely falling object is given by:
y = ½gt²
If we take y₀ = ½gτ² as the position after the first time interval τ, then:
- After 1τ: position = 1y₀
- After 2τ: position = 4y₀ (distance from previous interval = 3y₀)
- After 3τ: position = 9y₀ (distance from previous interval = 5y₀)
- After 4τ: position = 16y₀ (distance from previous interval = 7y₀)
- And so on...
This shows the distances in successive intervals follow the ratio 1:3:5:7... demonstrating Galileo's law of odd numbers.
Key observations:
- The distance fallen increases with the square of time
- Each time interval's distance is proportional to consecutive odd numbers
- The total distance fallen after n intervals is n²y₀
- The incremental distance during the nth interval is (2n-1)y₀



