Rocket Science - starting to look at investigations in a fun and active way!

1. ROCKET SCIENCE
Miss Amlani
Objec ti ve : Prep ar ing yo u fo r yo ur IIA ne xt
wee k by ge tt ing yo u to th in k ab ou t
ex pe rimen ta l te ch niques .

2. Levitating ping-pong balls
Turn the hair dryer on high and point it toward
the ceiling. Make sure to use a cool-air setting!
What do you think will happen if you gently
place the ping pong ball into the stream of air?
Will it blow away, drop to the floor or float? Try
it and see.
Key word: PREDICTION

3. Levitating ping-pong balls
The air leaving the straw blows the ping-pong
ball upwards, but what keeps it there and why
doesn’t it fly off and fall to the floor?
Key point: EXPLAIN your findings using
Scientific knowledge.

4. Why does it work?
The effect has been described in the 1930s by Coanda a Romanian
aeroplane designer. He showed that when air, or a fluid, flows over a
curved surface, it can stick to the surface and follow it, so the flow also
becomes curved. This means that when the ping-pong ball sits in the
centre of the air-stream, the flow traps the ball by passing around it on all
sides, sticking to its surface.
It remains in one place because of Newton’s Third Law (for every action
there must be an equal and opposite reaction.) If the ball tries to move in
any direction, the air sticking to its surface will be pulled with it. But if the
air is being moved, then there must also be a force pushing back on the
ball in the opposite direction, which is what holds it steady. This is why it
bobs about in one place.

5. How could we take this
experiment further?
See what happens when you:
- Try tubes that are longer or shorter or wider or
skinnier.
- Try to float objects in the air stream.
- Try to float two or more balls in the same air
stream. How many can you float at once? How
do they behave when there is more than one?

6. How does this apply in the
real world?
http://www.youtube.com/watch#!
v=YRrzcnBPpm4&feature=fvw
How can we use this to explain how the wing of
an aeroplane generates lift?

7. Liquid behaving badly
Is it a solid or is it a liquid? Make a really strange
mixture and find out how it behaves.

8. Liquid behaving badly
http://www.youtube.com/watch#!v=BN2D5y-
AxIY&feature=related

9. How does this work?
Cornflour is made up of lots of tiny (<0.01mm) starch particles, these are
very attracted to water so the water gets in amongst them very quickly.
The water acts as a lubricant, so when you move it slowly the particles
have time to move past each other and they can flow like a liquid.
However if you apply a rapid force it causes the particles to move slightly
causing the particles that are almost touching to jam together. and the
water that was between them moves sideways slightly into the gaps.
Now instead of having lots of lubricated individual particles you have a
solid structure of lumps touching each other which can't flow

10. How does this apply in the
real world?
http://www.youtube.com/watch?
v=qfhw6I_uBQg

11. Cola Volcano
You may have heard about the Mentos and Coke
experiment, find out how to make an erruption
with a drinks bottle, and what it has to do with
volcanoes.

12. How does it work?
A drink is fizzy, because it has lots of carbon dioxide ( CO2 ) dissolved
into it under pressure, while the pressure is maintained the CO2 stays in
solution. When you open the bottle the pressure is released, and the CO2
starts to come out of solution.
The bubbles need something to start to form on though and because the
inside of the drinks bottle is very clean there are very few places where
they can form, so it will take a couple of hours for the CO2 to be released.
The mints are really rough, so when you add them, there are lots of
places for the bubbles to form (if you added salt, sugar, sand etc it would
work too) so loads of bubbles are created all at once. This makes the
liquid hugely bigger forcing it to escape rapidly out out the top, in an
erruption.

13. More about the bubbles
Surface tension is the force that pulls water together into drops, and also
is trying to compress bubbles. Whatever the size of the bubble the suface
tension is the same.
A small bubble has a very curved surface which means that much of this
force is acting inwards compressing the gas inside.A larger bubble is
much less sharply curved so less of the force is acting inwards so the
pressure is lower.
If a bubble gets small enough the CO2 inside is at such a high pressure
that it will dissolve again, causing the bubble to collapse.
This means that there is a critical size of bubble, bubbles bigger than this
grow and bubbles smaller shrink. So normally no bubbles can form,
however if you drop a mint in water the rough surface will make it easier
for bubbles to form, as water doesn't stick to sugar as well as other water,
and because it will drag little air bubbles along with it trapped in amongst
the rough surface.

14. How does this apply to the
real world?
There are many types of volcano, but the ones
that errupt explosively, have lots of gas dissolved
in the magma. If the pressure builds up and then
is suddenly released, these gasses form bubbles,
and expand to thousands of times their original
volume throwing, rocks, ash and pummice
kilometers.

15. Variables
The variable which is chosen for an investigation
by the person doing the experiments is called the
independent variable.
The thing being affected is called the dependent
variable.
The factors you keep the same in your
experiments (fair test) are called control
variables.
The independent variable is plotted on the x-axis
of a graph.
The dependent variable is plotted on the y-axis.

16. Your Turn
Design an investigation using any of the
experiments you have seen today in small groups
(of no more than 3).
What are you investigating?
What will you be measuring?
What is your prediction?
What will your method be?
What are your variables?