Experiment 1: Free Fall

PURPOSE: To study the motion of a freely falling object, determining the acceleration due to gravity.

APPARATUS: An object suspended from an electromagnet falls when the magnet is turned off. As it falls, its position is periodically recorded by electric sparks: Every sixtieth of a second, a high voltage pulse is sent to the wire next to the falling object, making a spark jump to a metal ring on the falling object and from there to another wire behind the strip of paper. As the spark goes through the special paper, it leaves a mark.

CAUTIONS:

As a safety precaution, do not use the apparatus without someone else in the room to pull the plug if you are being shocked.

Do not move the apparatus, or you may throw it out of level so that the object doesn't fall correctly into the pot.

PROCEDURE.

1. When your group's turn comes, run off a tape:

a. Turn on the electromagnet with the key on its power supply.

b. Suspend the object from the electromagnet and steady it so that it hangs motionless.

c. Turn on the switch on the face of the spark source, which should be set for 60 Hz. Pick up the hand pushbutton and push it to turn on the sparks.

d. Switch off the power supply to drop the object. When it lands, take your thumb off the button and turn off the switch on the face of the spark source.

2. Handle the tape with care. It's easy to leave marks you might later mistake for sparks.

3. Choose points near, but not at, each end of the tape and label them i and f as shown below.

4. Determine the object's velocity at point i by finding its average velocity during an interval centered on point i, as follows:

a. Go the same number of sparks to either side of point i, then measure Δx between these sparks. If any dots seem not to have printed (each interval should be just a little larger than the one before), be sure to count as if the missing dot were showing. If several are missing, show the instructor.

b. Determine Δt between these same sparks by counting 1/60th second intervals. (Count spaces, not dots. In the example above, four spaces correspond to the distance of 14.3 cm, so Δt = 4/60 second.)

c. Find the velocity from the distance and time.

Example: For the spark tape above, the speed at point i is:

Δx = 14.3 cm = 14.3 cm = 214 cm/s

Δt 4/60 s .0667 s

5. Repeat for point f.

6. Find the change in the object’s velocity between dots i and f.

7. Find the time between points i and f by counting the spark intervals between i and f.

8. Calculate the object’s acceleration.

9. Under CONCLUSION, state what the accepted value for the acceleration is, and comment on whether your result is reasonably close to it.

Report on Experiment 1: Free Fall

Name __________________________________________

NOTE: ON ALL LAB REPORTS,

- Work in pencil (or work out your mistakes on a first draft)

- Hand it in or have me initial it before leaving the laboratory.

Initially:

Δx =

Δt =

v_i =

Finally:

Δx =

Δt =

v_f =

Between points i and f:

Δv =

Δt =

a =

Conclusion: