Free fall
Section: Kinematics | Syllabus: Cambridge AS Level Physics (9702)
Acceleration of Free Fall
Free fall occurs when an object falls solely under the influence of gravity, with no air resistance. In a uniform gravitational field (like near the Earth's surface), all objects fall with the same constant acceleration.
Acceleration of Free Fall (g) The constant acceleration of an object falling in a vacuum.Value: g ≈ 9.81 m s^-2 Important
In the absence of air resistance, the mass of the object does not affect its acceleration. A feather and a hammer would fall at the same rate in a vacuum.
Experiment: Determining g
A common method to determine the acceleration of free fall (g) involves measuring the time it takes for an object to fall a known distance.
Electromagnet and Trapdoor Method
- An electromagnet holds a small steel ball at a measured height (h).
- Switching off the electromagnet starts an electronic timer and releases the ball.
- The ball falls and hits a trapdoor, which breaks a circuit and stops the timer.
- The time (t) is recorded.
Using s = ut + (1/2)at^2:
Since u = 0, s = h, and a = g, the equation becomes:
h = (1/2)gt^2
Rearranging for g: g = (2h/t^2)
Reducing Errors- Measure the height (h) from the bottom of the ball to the top of the trapdoor to avoid systematic errors.
- Repeat the timing at different heights and plot a graph of h against t^2.
- The gradient of the graph will be (1/2)g.
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