Time Intervals of Falling Objects

Purpose:
To demonstrate the acceleration due to gravity.

Equipment:
Metal plate with two strings each with metal pieces attached

Equipment Location:
Other

Procedure:
First take the string with the metal pieces evenly spaced (the one with the smaller metal pieces). Either stand on the table or have a student stand on the table and hold the string up until it is tight. Drop the string from directly above the metal sheet so that the metal pieces strike the metal sheet. You should hear the interval between the sounds get shorter. Next take the string with the larger metal pieces and hold it up until it is tight. Again allow the string to fall directly onto the metal sheet. This time the spacing of the metal pieces should make the intervals between sounds equal.

Hints:
Some practice may be needed to ensure that the metal pieces strike the metal sheet to create the sounds needed. This is another case where you can ask the class which they think will cause the equal intervals before showing them which will.

Relevant derivations/explanations:
In order to create the string that causes the equally spaced sounds we used the formula: xo=vot+[1/2]at2 We decided that we wanted the sounds to be .2 seconds apart and we also rounded the acceleration to 10. Using these numbers the gaps between the metal pieces are 20cm, 60cm, and then 100cm. The string where the sounds speed up are spaced equally with a gap of 80cm which means the time interval between the sounds is .2701 seconds for the first interval, .1569 seconds for the second interval, and .1231 seconds for the third interval.