Use a stopwatch and a metre rule to measure the average speed as an object falls from a table to the ground. What are the difficulties and how might they be reduced? Some of the suggestions will be the same as those in Experiment 2, but you should also consider difficulties in measuring the distance to the ground and how they can be avoided. Remember, rules have battered ends and the ends may not be at 0 and 100 cm.

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Problem Improvement "Taking readings for just two masses was not enough. 'I should use a great range of different masses and plot a graph of the average time to fall to the ground against the mass of the object.' 'It was difficult to start the stopwatch at the same instant that in the background. When the video is played back, frame by frame, I dropped the stone and to stop it exactly as it hit the ground. I may have been late because of my 'Film the fall of each stone with a video camera which has a timer I will see the time when the ball hits the ground on the timer. "(Alternatively, you can use light gates connected to a timer to measure the time electronically. You should draw a diagram, explaining that the timer starts when the first light gate is broken and stops when the second is broken.) reaction time.' 'My hand was not steady and so I may not have dropped the stones from exactly the same height each current in the electromagnet is 'Use iron objects which hang from an electromagnet. When the electromagnet holding iron ball eye switched off, the object falls.' (A diagram would help - see Figure P.15.) time.' line of sight "The heavier stone was larger in size and it was important that the "Clamp a metre rule vertically and start the bottom of each stone at bottom of each stone started at the exactly the top of the ruler each same height. There may have been time. To avoid parallax error, I will make sure my line of sight is horizontal, at right angles to the rule.' (A diagram will show this clearly - see Figure P1.15.) set square to make rule vertical parallax error.' Figure P1.15: Using an electromagnet iron objects. The line of sight is clearly shown. to release The times that I measured were verv short - not much areater than I make the uncertaintv in each time measurement smaller in my reaction time - so reaction time proportion to the time being measured.' had a great effect. 'Increase the distance of fall so that the times are larger. This will