SUBJECT AREA: Physics Concepts including Gravity, Acceleration, and Freefall

MATERIALS:

1. Two sets of seven splitshot fishing weights.

2. Two, 250 cm strong thin threads (monofilament fishing line).

3. Two metal cookie sheets.

PROCEDURE:

1. Tape one end of the fishing line to the cookie sheet and fasten the fishing weights so that the first weight is 30cm above the cookie sheet. Fasten each of the other weights so they are 30 cm from each other.

2. Construct supports under the cookie sheet so it is a few inches off the floor (this will improve the sound produced by the falling weights).

3. Stand on a chair and hold the line tight above the cookie sheet. Release the thread and note the rhythm of the sound as the weights hit. Note also the time interval between percussions.

4. Clamp the seven other weights to the other thread the following distances from each other: cookie sheet to 1st weight 5 cm, the next seven: 15,25,35,45,55, &65 cm from each other respectively. *

5. Repeat step #3.

6. Repeat both demonstrations, alternately, several times

* At teachers discretion, one can either give the correct measurements or have the students calculate the proper measurements or find them through trial and error.

QUESTIONS:

1. What were the differences in intervals (even or increasing intervals) between the first demonstration and the second?

2. Which of the weights had the highest velocity when hitting the cookie sheet? What was this velocity in m/s?

3. What kind of motion is the free fall of the weights?

4. What gives a falling object its acceleration?

RATIONALE:

The falling weights are all independently subjected to gravity. The force of gravity imparts an accelerated (ever increasing) motion to each of the weights. This acceleration is constant because of Newton's Second Law, (F=MA). Since the Force and Mass of the weights are equal, the acceleration of each of the weights is the same. The difference is that the further or "longer" the weight falls, the greater the velocity (v=at) of the weight when it hits the cookie sheet.

The distances between weights in the second demonstration were obtained from:

d=1/2 gt2 (d= distance, g= accel. of gravity, t= time)

When the weights are placed at regular intervals, the arrival is irregular, getting faster and faster (ever increasing), due to increased velocity (acceleration of gravity x time). The weights in the second demonstration also have equal increasing velocity, but because of the increased distance between weights, they arrive at even intervals.

APPLICATION:

A falling object increases velocity proportional to the time of fall. A high fly ball goes up and falls down with more velocity than a pop fly, but it takes longer for a high fly ball to come down because of the distance (v=dt) it travels due to an increased velocity.