Transcript 4E - Group 4

1. Materials Used
2. Design
3. Application of Physics Principles
4. Results of Experiment
5. Conclusion and Discussion
6. Comments of Group Members
Polystyrene
Cotton
Plastic string
Linen
Plastic bag
Rubber band
Plastic bag
Plastic string
Polystyrene
Cotton
The length of plastic strings affect the effective
parachute surface area. It is the actual surface area of
parachute that affect the air resistance. The longer the
plastic strings, the smaller the angles the plastic strings
made with the vertical. Then the horizontal component of
tension of plastic strings Tsinθ becomes smaller.
So the effective parachute surface area increases and
air resistance increases too.
The surface area of parachute should be large to
increase air resistance. Air resistance can balance the
weight ( gravitational force). Then there is no net force
acting on the parachute hence no acceleration. The final
speed is called terminal speed. When the air resistance
increases, the parachute reaches its terminal speed
within a short time as the acceleration is decreasing.
By F=(mv-mu)/t, when the final landing velocity
decreases, the impact force decreases too.
The mass of parachute should be as small as possible.
By F=(mv-mu)/t, when the mass decreases, the impact
force decreases.
The lower part of parachute should be wrapped with
cotton and polystyrene. When the lower part of
parachute hits the ground, the cotton and polystyrene
contract because of pressure. Hence the impact time
increases. By F=(mv-mu)/t, when the impact time
increases, the impact force decreases.
1. The egg and the parachute landed safely from
fourth floor in the New Wing of our school to the
ground. The egg did not break.
2. The parachute reached its terminal speed within
a very short time.
3. During the falling, the parachute fell down
directly. It did not hit anything.
4. It took about 4.8s to reach the ground.
Conclusion:
All the following factors ensures the egg to be safe:
• Surface area of plastic bag (increase air
resistance)
• Cotton and polystyrene (shock absorber)
• Small mass of parachute (reduce impact force)
• Long plastic strings (increase the effective
parachute surface area)
Discussion:
The parachute could perform better if the following
things are done:
1. The surface area of plastic bag becomes larger to
increase air resistance.
2. The appearance of the lower part of parachute
can be modified.
At first, we thought a parachute for an egg can be
easily made. But during the making process, we found
that it was quite difficult to decide on the appearance
and the materials to be used.
Before we surfed on the Internet, we did not know that
even the number of strings also affect the falling of
the parachute. Although we spent lots of time to
prepare this project, we were happy when we knew
that the egg did not break after the experiment and
all of us have learnt a lot from it.