Return to Physics IndexDisplacement of Fluids

Thomas J. Billups Delano Elementary

3937 W. Wilcox

Chicago IL 60624

(312) 534-6620Objectives:

This activity was designed for grades 4th thru 8th. Students will acquire a

working definition of the word "displacement". Students will also understand

that the volume (size) of an object placed in water affects the amount of water

that is displaced.Materials Needed:

Students will be in groups of 3-4 individuals. Each group should have the

following items:

2 liter bottles (tops cut away) 3ea.

300 gram weight 1ea.

800 gram weight 1ea.

1200 gram weight 1ea.

1 liter graduated cylinder 1ea.

balancing scale 1ea.

styrofoam cup 1ea.

1/4" plastic tubing (ink pen shell) 1ea.

2 objects same weight (500-1200grams) but different volumes

2 objects same volume but different weights (1 plastic block & 1 styrofoam

block)

The 2 liter bottles are converted into overflow containers by taking a Phillips

screw driver and heating the tip and using the tip to melt a hole into the

container. The hole should be 3cm - 4cm from the top of the container. Next,

place the 1/4" tubing into the hole, making sure to get a tight fit. The tubing

allows for all the water from the container to flow into the graduated cylinder.

* Note the water level should be at the point that water flows thru the tubing

then stops. This level should be reached before performing exercises 2 thru 4.

Strategy:

Students will be introduced to the concept of displacement by observing the

following exercise. Take two 2 liter containers filled 3/4 of the way with

water. A 200 gram weight is placed in one of the containers of water and a

1,000 gram weight placed into the other container. Students should notice that

the water levels have increased. Students should also notice that the container

with the 1,000 gram weight has the higher water level. Students are then

informed that, in each case, the change in water levels is a measure ofdisplacement.

Displacement is the amount of change in fluid volume from the initial point

(beginning water level) to an ending point. Students are then asked to construct

a definition of the word displacement based on their observations. Students are

then asked to theorize as to what led to the different levels of displacement.

Most students tend to theorize that the heavier objects' weight leads to a higher

water level. Students are now ready to perform the following experiments to

test their theories. Have students form groups of 3 or 4 individuals, so that

each group will conduct the following experiments.

Experiment 1:

Place the various weights (300, 800, and 1200 grams) into different identical

containers and notice the change in water levels of the three containers. Once

again, students should notice that the greater the weight in the container the

higher the level of displacement. This observation may lead to the conclusion

that the weight of an object affects the amount of water that a object

displaces.

Experiment 2:

On a balance scale have students weigh the two objects of the same

weight but different sizes. Next, place each object into an overflow

container and measure the amount of water displaced. Any object that floats

should be held below the water level, until the (displaced) water empties into the

graduated cylinder. Students should notice that the object with more volume

(greater size) displaces more water. Students conclude that it is an objects'

size that determines the amount of water displaced. To prove the findings of

experiment 2, perform experiment 3.

Experiment 3:

Place the two objects of similar volumes and different weights into the

overflow containers. Students should notice that both objects displace similar

amounts of water, which would substantiate the findings of experiment 2.

Experiment 4:

Now place the 300 gram weight into the over flow cylinder and record the

amount of water displaced. Next, hold an inverted styrofoam cup submerged under

water and record the amount of water displaced. Once again, students should

notice that the cup displaces more water than its weight, further illustrating

that it is the volume of an object that determines the amount of water that the

object displaces.Performance Assessment:

Students will receive a maximum of 20 points for each experiment completed. A

two question essay (20 points) will also be administered. A maximum of 100 points

is possible.

100-90 = A

89-80 = B

79-70 = C

69-50 = D

49-20 = F

19-0 = 0

References:

"Archimedes' Principle",Encyclopedia Britannica, 1991.