Measurement of g

In this experiment a ball is dropped from an electromagnet onto a trapdoor. When the ball is released a timer is started. When the ball hits the trapdoor the timer is stopped. If the distance from the ball to the trapdoor is measured the acceleration due to gravity (g) can be calculated. Using the formula; s = ut + ½at² and noting that u = 0 and a = g

s = ½gt² => g = 2s / t²

Procedure:

1. Press "Get Ruler". Measure and record the distance from the trapdoor to the bottom of the ball (s)
2. Press "Release B" to release the ball and start the timer. Record the time (t) for the ball to fall the measured distance. In the physics lab. the ball should be allowed to fall at least three times and the shortest time recorded. Not necessary here.
3. Press "Replace B".
4. Press "Rise Trapdoor". The trapdoor rises by a random amount thus changing the distance through which the ball will fall the next time
5. Repeat steps 1 to 4 until at least six sets of results are collected
6. Press "Reset" to repeat the experiment

Analysis:

Calculate g for each s value and its corresponding t value using the formula given above.

Plot a graph of s (y-axis) against t². Draw a "best fit" straight line and measure its slope. Since s = ½gt², the value of g is calculated by g = 2 × slope.

Precautions:

• Record the shortest time of fall for each height
• Place a piece of paper between the ball and the electromagnet to ensure that the ball falls immediately when the switch is flicked
• Use large distances as much as possible so that measurement errors (distance and time) are relatively small