1.
Forces
At the
very beginning there was an explosion. They call it the Big Bang. What happened
before is a mystery, a mystery unsolvable.
That
very first explosion released an enormous quantity of energy. MOVEMENT was
created. Since then this energy has spread, it is all around us. It forms
matter and it appears in the shape of forces.
*
Forces
move and change things. You kick a ball and it flies. It moves through the air.
It hits your teachers head. The head moves. The whole body moves, the coffee
is spilt... You model plasticine, and with your fingers you give it
different shapes.
Forces
are behind all this. Forces make thing move. Forces change thing.
2. Push
and Pull.
Foces
either PUSH you, send you away; or PULL you, attract you. We could almost call
it Love and Hate, or Come and Go. But we have decided to call it PUSH and PULL.
Gravity pulls things together. Rafa Nadal shoots the ball away with his racket.
On some doors you have to pull, on others you have to push.
The
distinction is not always clear. Ask yourself what forces happen in swimming,
Push or Pull forces?
*
In
Science we represent how Forces act using arrows. Look at this picture: HERE.
The
arrows represent the direction of the Force.
The
size of the arrow represents the power (the Newtons) of the Force. Look: HERE
So in a
A/ <--- and B/ -------> situation (for example 2 students
fighting for a pencil), the second student wins.
3.
Gravity
At the
very beginning people thought the universe was naturally flat. thing fell to
the ground naturally. Discovering the world was round was a shock for many. If the
world was round, the people at the bottom of the sphere would fall off. Think
about it, its logical. Get a football and a toy. Position the toy on the north
pole. It stays. Now try the same on the south pole. It doesn´t stay. It falls
off. We thought in a similar way. It is impossible to have a round world, the
would say, because people in the south hemisphere would fall down into space.
*
But
this did not happen. A very special force came into play: GRAVITY. Gravity is a
pull force that makes all material thing attract each other.
So the
sun attracts the earth (and the earth tries to attract the sun), the earth
attracts you (and you try to attract the earth), you attract your pencil (and
your pencil tries to attract you), your pencil attracts...
The
amazing Isaac Newton was especially interested. Came out with the formula. Look HERE
*
-This
complicated formula simply tells us that bigger objects will win in the pull
battle, and that the power of this pull force will depend on the distance
(things that are near each other feel bigger gravity.)
So, the
pull of the earth on a person is stronger than the pull of a person on the
earth. So we only feel one attraction.
It also
tells us that the bigger the object (compared to the smaller one) the bigger
the gravity.
The
water feels the pull of the moon. This pull is not big enough for the water to
fly into the sky, fly into the moon, and stay there. But what we do feel is
that the sea has high tide and low tide because of this. LOOK
and HERE
*
As you
have read in the previous paragraph, the pull force of the earth changes
depending of the distance. Look at newton again here .
The bigger the separation, the smaller the G (gravity) force. So
- A
spaceship abandoning earth needs a big push force coming from its rockets. But
as it flies up into space, the push force needed becomes smaller because the
separation is bigger (the G force is smaller). Read this again.
-When
it reaches a certain separation, a certain distance, the G force is so so
small, nearly zero. Then we have GRAVITY ZERO!!!! Everything weighs here 0kg.
4. G in
Moon and other planets.
After
what we have just learnt let´s take a look at G force in different places.
We all
know what G is like here, on this planet. If I ask you what your weight is, you
go on a scale at you answer: 30 something or 40 something or 50 something etc.
We
travel to the moon. As we abandon the atmosphere G grows smaller (remember:
distance). we reach outer space, what we call gravity zero, and we float.
We land
on the moon. the moon has got 6 times less mass ( 6 times less material). If we
could weigh it, it would weigh 6 times less than the earth. We say the moon is
6 times smaller than earth. So, ...what happens to gravity here?
G is 6
times smaller!
This
means that if you weigh 36 kilos here, in the moon you would weigh...6 kilos!
You weigh 42 kilos here, in the moon 7 kilos!!!!!
If you
can jump 50cm high here, in the moon with the same muscles 6 times higher. That
is 300cm high, 3 metres!!!!!!!
5.
Water Resistance
The
weight of the titanic was 52, 310 tonnes. That is 52,310,000 kilos. Not bad. It
was not made of wood, nor plastic. It was made of metal, yet it floated!!!!!!
This is not much compared to The
Freedom Ship.
How can
this super heavy metal thing float!!!
Archimedes
The Greek is famous for running out of his bath naked shouting
"Eureka". Easier to shout Eureka than to shout. the upward
buoyant force that is exerted on a body immersed in a fluid, whether fully or
partially submerged, is equal to the weight of the fluid that the body
displaces.
This
complicated statement means that any object put into water will feel an
upwards push that is equal to the water it removes with its weight.
An
elephant in a pool will remove a big amount of water ( the water level will
raise). The elephant will receive an upward force equivalent to that quantity.
A
little pea will remove bery little water, so nthe upward force will also be
little.
What
effects does it have on the weight of things. Look Here.
Explanation
(only if you need it):
The
weight of the object was 7kg out of the water.
The
object when inmersed into water displaces 3 kilos of water.
According
to Archimedes the upwards push will be of 3 kilos
The
weight of the object inside of the water is 7k -3kg = 4kg
6.
Magnetism
Look HERE. All clear, right?
7.
Friction.
I am
sure this scene is familiar HERE.
You are running, you fall on your knees and ouch. The floor was simply
trying to stop you from sliding, but it did it in a very agressive way. But
this situation HERE is
different. These youngsters are not bruising their bottoms. These are
having fun too.
The
reason is simple: Some surfaces are flat, smooth and slippery. Other surfaces
are abrasive.
Friction
is a force that stops objects that move. Look: HERE.
The big red arrow is a push force moving the block. The little red arrow is the
contact force (friction) that stops the block from sliding. In this image the
block moves because the push is bigger than the friction.
Build a
ramp at home with some books. Let a marble role down the ramp to the floor.
measure how far away it goes.
Now
take the SAME marble and the SAME ramp to a room with a DIFFERENT floor. For
example a carpet, or the garage. Roll the marble, aand measure the distance.
What is the difference?
The
marble that rolled the less was stopped by higher friction.
The
marble that rolled the most was stopped by lower friction.
But
never think that friction is an evil force that was created to stop the happy
movement of objects. Here we have two wonderful examples of bery little
friction:
Friction
helps in the control of machines. Big friction means big control. Look HERE. Casey Stoner
depends on his tyres, on the high friction that will stop the sliding. HERE is
the state of a tyre that has done its work after a F1 Grand Prix. It kept the
car on the track. Check the angle of the bike in this amazing photo HERE.
Tyre companies work on how to increase friction and stop bikers from sliding.
Climbing shoes need to increase friction rate too HERE.
A train
is very heavy. its metal wheels roll on the metal railroad. Friction here is a
problem, because it stops the train making it slower, and wastes petrol
(because the train needs more push from the engine). An engineer found such a
clever system to reduce the train´s friction to zero!!!! How?
By
using magnets!!!!!!
The
installed on the bottom of the train magnets. Then they put on the rails
magnets of the same pole (positive and positive). This created an effect of
repulsion. The train floats on the rails!!!!!!!
Look at
this diagram.
The
green bar represents the rails. The blue bar represents the floor. As you can
see, positive and positive repel each other and the train floats.
Look here,
find the video here.
Make your own here. These ones is so
cool
8. Air
Resistance
Aerodynamics
is the way vehicles like cars, planes, bikes confront the force called Air
Resistance.
Air
Resistance is also a stopping force. When you go on your bike, the air hits
your face and body. This slows you down. The way to stop this is HERE.
Changing the position of your body.
The
same happens in ski. Look
F1 cars
are experts at using Air Resistance. here
But
sometimes we are not interested in avoiding Air Resistance. Sometimes Air
Resistance is needed. This happens when we are flying. This also happens when
we are going too fast or falling.
Parachutes and here
RedBull
Flyers or here or here
So, Air
Resistance is a force that works against an object that moves stopping it.
9. Play
and Learn
Find
here Forces,
Friction, Magnets
Lots
here in Wonderful
Woodlands
For the
brave HERE
