Acceleration of Free Fall Experiment
- A common experiment to determine acceleration of a falling object which can be carried out in the lab
Apparatus
- Metre rule, ball bearing, electromagnet, electronic timer, trapdoor
Apparatus used to measure g
Method
- When the current to the magnet switches off, the ball drops and the timer starts
- When the ball hits the trapdoor, the timer stops
- The reading on the timer indicates the time it takes for the ball to fall a distance, h
- This procedure is repeated several times for different values of h, in order to reduce random error
- The distance, h, can be measured using a metre rule as it would be preferable to use for distances between 20 cm – 1 m
Analysing data
- To find g , use the same steps as in the problem solving section
- The known quantities are
- Displacement s = h
- Time taken = t
- Initial velocity u = 0
- Acceleration a = g
- The equation that links these quantities is
- s = ut + ½ at2
- h = ½ gt2
- Using this equation, deduce g from the gradient of the graph of h against t2
Sources of error
- Systematic error: residue magnetism after the electromagnet is switched off may cause the time to be recorded as longer than it should be
- Random error: large uncertainty in distance from using a metre rule with a precision of 1mm, or from parallax error