Parachutes at sunset                    Parachutes               chutes from plane   by Rebekah Corbett


    When an object moves through the air, it has to push the air molecules out of the way. This creates a resistance force, or drag, on the moving object. So, the harder it is to push the air out of the way, the slower it moves. The large drag generated by a parachute help in reducing the payload's fall speed by acting against the payload's weight.


Building a Parachute:
    For this activity, the class will need to be split up in to four groups (there can be more or less group depending on the number of varibles you want to test). Each group will make one control parachute and two other parachutes that differ by the varible they are testing. So if they are group 1 they are testing weight and they will have one control chute,  one with more weight then the control and one chute with less weight then the control.

For the groups suggested here you will need:
Have the students start with the 12" square of plastic. Cut it out in a circle with a 12" diameter by measuring or by folding and cutting plastic as shown below. Then cut six holes equally around the outer edge of the circle. Tie one string to each hole. Collect all six strings and tie them to your weight (the two paper clips). You now have your control chute. For each of the varibles each group is testing, change only that one varible and keep the rest the same. So if a group is  testing the size of the chute only change the size of the chute, not the fabric, number of strings or the weight. This will skew the restults. Then once your first group is done (or you could wait until everyone is done) test your parachutes by dropping them from a high place (a staircase works best but a ladder or chair will do) and see which one falls the fastest. Each group will drop two parachutes at a time; their control and one of the chutes they are testing. This experiment takes a minimum of 15 minutes depending on how many varibles are being tested. With four varibles it might take 20-30 minutes depeding on the speed and the grade level of the children you are working with. More tests can be added to make it longer.

How to make a circle:
    Start with a 12" square of plastic. Fold it in half. Then fold it in half again, keeping track of the original center of the square. Then fold the folded square diagonally in half so it forms a kind of diamond (see pictures). Remember to always fold so the fold goes from the center of the orginal square to the furthest corner. Keep folding the same way until you can't fold anymore. Also making sure to keep the shortest fold on the outside. Then cut the plastic at the shortest layer. If you cut at the wrong place it will be a square with rounded corners, simply fold it again and cut at the shortest layer. If you get a bunch of pieces of plastic and no one shape, then you did not keep track of the center and you must start over again. Below are pictures to show the folding steps.

square 1st fold 2nd fold 3rd fold 4th fold 5th fold  showing layers  cut shortest layer

Then unfold, tie on stings and attach weight.
 
   circle   with strings on   finished chute

Here is the chart for what each group is testing. Give one to each student so they know exactly what they are constructing and what everyone else is doing as well.

Group 1

Varying  Weight

Group 2

Varying Size of Parachute

Group 3

Varying Number of Suspension Lines

Group 4

Material of Chute
Control  parachute design but with  1 paper clip Control parachute design but with a diameter of less than  12” Control parachute design but with  4 suspension lines (strings) Control parachute design but with  black (thinker) plastic parachute

Control

12” parachute  diameter, 2 paper clip, six 12”  strings and white plastic bag

Control

12” parachute  diameter, 2 paper clip, six 12”  strings and white plastic bag

Control

12” parachute  diameter, 2 paper clip, six 12”  strings and white plastic bag

Control

12” parachute  diameter, 2 paper clip, six 12”  strings and white plastic bag
Control parachute design but with more then 2 paperclips Control parachute design but with a diameter of more than 12” Control parachute design but with  8 suspension lines (strings) Control parachute design but with  a cloth parachute


Explanations for findings:
     Group 1: They should find that the more weight is added to the chute the faster the parachute falls and the less weight the slower it falls. This is because as they increase the weight there is more gravity acting on it, pulling down on it more. Since the drag is the same (no other varables changed) the parachute falls faster then the control.
     Group 2: They should find that the greater the radius the slower it falls. This is because the larger radius has more drag. With the increase in diameter the air molecules have to travel further to get out of the way of the object.
     Group 3: They should find that the parachute with only four lines does not quite have enough strings to catch the air molecules. The parachute with 8 stings should also fall slower then the control becasue as the number of stings increases, the effective parachute surface area will decrease.
     Group 4: They should find that both the heavy trash bags and the fabric should fall faster then the control. The thicker or heavier trash bag will fall faster becasue it is actually adding weight to the parachute. The fabric parachute falls faster becasue it actually has small holes in the fabric that is allowing small amount of air through as it falls. This decreases the amount of air having to be pushed out of the way and makes it fall faster.    

The information for this experiment came from two sites.  There are also additional design ideas and different explanations available.
http://www.pcprg.com/sptp.htm
and http://www.seed.slb.com/en/scictr/lab/drop/notes.htm

More designs can also be found at  http://www.pbs.org/wgbh/nova/teachers/activities/3101_mars_02.html