UNIT_4. MACHINES

MACHINES

1º INTRODUCTION.

2º WORK.

3º SIMPLE MACHINES.

4º COMPOUND MACHINES.

                             
Book unit nº12: "INNOVATION": How does it works?

1º INTRODUCTION. 

Leonardo da Vinci was a famous painter and inventor. He lived 500 years ago, but you can still see his creations today. You can see his paintings in museums, but you can also see his inventions everywhere! LIKE THIS MACHINES: bicycle, parachute, submarine and the compass.

MACHINES are devices tha allow you to work easier, better and faster. They help you save time and energy.

We use machines every day. Some machines can be dangerous: you can cut yourself with a sharp knife, you can burn yourself with the cooker, you can get an electric shock from touching a plug.

2º WORK. 
 There are two ways of lifting a box onto a table (By hand or using a ramp). It can be said tha the work performed (the energy needed to lift the box) is the same in both cases: Using the ramps rquires less force, but the distante becomes longer. 

WORK(Joule) = FORCE(Newton) * DISTANCE(Metre)

Machines transforms energy into work, but not all the energy gets tranformed into useful work because losses occur, in order words, machines do not have a performace rate (effciency) of 100% because some energy gets lost.

Efficency(%) =(Useful Work / Energy Input) * 100.

Example: To raise a box by 1metre, a force of 500N is required. It is know that the motor absorbs 650J of energy in this process. 
a) How much work does motor perfor? W=F*D= 500*1 = 500J.
b) What is the efficiency(%):   n= Uselful Work/Energy Input * 100 = (500/650)*100=76.92%.






3º SIMPLE MACHINES.

Video: "Introduction" in YouTube.

Video: "Simple machines" (Song of YouTube). 

The simple machines are SIX and all of then have one or few parts. There are simple machines in every where: a hammer, scissors, knife, etc.


a)YouTube:  SIX SIMPLES MACHINES 
b)Toy Tube:  SIMPLES MACHINES 
c)PDF:  SIMPLE MACHINES
d) ACTIVITY: LISTENING: "THE FIRST MACHINES"
  

1.- THE FIRST MACHINES.

People invented the first machines a long
time ago. They were simple tools made of
stone, wood, or bone.
About two million years ago people made
stone axes with wooden handles. They used
these tools to cut wood. People also used
stone and animal bone to make knives and
arrows. To shoot their arrows they used
bows made with long pieces of wood.
People used simple levers to move heavy
objects like rocks. They put one end of a
long stick of wood under a big rock, and
they put a small rock under the stick. When
they pushed on the other end of the stick,
the big rock moved.
About 7,000 years ago people started
farming for food. They invented new
rnachines, like plows, and used animals to
make work easier. Some farmers used long
levers to get water from rivers. They also
built canals to get water for their plants.
About 5,000 years ago people started
making metal tools. These tools were
better than stone or bone tools.

  

LEVER:  

a) First degree levers: SCISORS, CLOTHESPIN, HAMMER.

b) Second degree levers: NUTCRACKER, WHEELBARROW, BOTTLE OPENER.

c) Third degree levers: TWEEZERS, HAMMER, SHOVE.  

Force*Lf = Resistance*Lr

THE PULLEY 
These are different types of pulley systems:

• Fixed: A fixed pulley has an axle mounted in bearings attached to a supporting structure. A fixed pulley changes the direction of the force on a rope or belt that moves along its circumference. Mechanical advantage is gained by combining a fixed pulley with a movable pulley or another fixed pulley of a different diameter.
• Movable: A movable pulley has an axle in a movable block. A single movable pulley is supported by two parts of the same rope and has a mechanical advantage of two.
• Compound: A combination of fixed and a movable pulleys forms a block and tackle. A block and tackle can have several pulleys mounted on the fixed and moving axles, further increasing the mechanical advantage.

• F_Z = Rope tension or effort force
• F_L = Load or resistance force
• s = Rope displacement (distance pulled) or effort distance
• h = Height (distance load is raised) or resistance distance

An illustration showing how pulleys are used to obtain a mechanical advantage. Using additional pulleys decreases the force required but increases the distance required to raise a load the same amount. In each instance here the mechanical work done is the same, work being the product of force and distance.

• F_Z × s = F_L × h
  • 10 cm × 100 N = 10 J
  • 20 cm × 50 N = 10 J
  • 30 cm × 33 1/3 N = 10 J
  • 40 cm × 25 N = 10 J

4º COMPOUND MACHINES.
The compound machines are made up of two or more simple machines working together: motors, gears, electric circuits. For example: a car, a airplane, * Steam Machine.(PDF).

ACTIVITY: Listening.

2.-"THE WHEEL"

The wheel is one of the most important
inventions in history. About 5,500 years ago
potters used the first wheels to make clay
pots. They put wet clay on a wooden wheel.
Then they turned the wheel to make a nice
round pot.
Before people had wheels to move heavy
objects, they used rollers. The rollers were
made from tree trunks. Then people made
carts and chariots with wooden wheels.
They connected the wheels with a long bar
called an axle
Today there are lots of machines with
wheels. We can see wheels on cars, bicycles,and skateboards.
There are also wheelchairs for people who can't walk
easily. Can you think of more machines that have wheels?
(The London Eye is a very big wheel. It´s 135 meters high.You get a great view of London from the top).

 
3.- RAMPS AND CRANES. 
Ramps are useful because they help us lift
objects more easily. More than 5,000 years
ago the Ancient Egyptians used ramps to
build pyramids. The Great Pyramid at Giza
is the biggest pyramid in the world. It's 138 meters high.
The Egyptians used rollers to move large
blocks of stone up the ramps. They needed
lots of workers because the blocks were
very heavy.
About 2,500 years ago the Ancient Greeks
used big cranes to build temples. The cranes
were made of wood, and they had many
ropes and little wheels called pulleys. First
the workers tied a rope to a block of stone.
Then they put the rope around the pulley.
They pulled the rope and lifted the block.
The work was easier with cranes, so the
Greeks didn't need as many workers as
the Egyptians.

  

ACTIVITIES:

1.- Name there machines with one or few parts, and three machines with many parts.
Polley, lever, inclined plane. Computer, calculator, car.

2.- Calculate the work requiered to lift a weight of 1200N to a height to 9m. 
10800J

3.- A person pushes a suitcase across a railway station of 20m. It the total performed is 1200J, How much force had to be applied?.
60N.

4.- Find out how many simple machines are combined in a wheelbarrow.
Lever, inclined plane.

5. Complete the sentences:

• a) Machines are objects that help save effort.
• b) Planes and cars are complex machines.
• c) All machines need energy to function.

6. Complete a sentence of these objects where you describe the ENERGY that they use for. 

• a) vacuum. Battery and hand pushing.
• b) helicopter. Burning fuel.
• c) stapler. Hand force.

7. You should always take care when using machines. Think of these machines that you can use and write how they can be dangerous and give a safety rule.

• a) Knives: We can cut ourself. We shouln´t play with them.
• b) plug: You can electrocute. You shouldn´t touch it. 
• c) jigsaw: You can cut. You shouldn´t use it without protection.
• d) glue pistol: You can burn with it. You should be careful when using.
• e) drill: You can make a hole on your hand. Be careful when drilling.

8. What sort of  SIMPLE MACHINES are these objects?:

•  a baseball bat : Lever
•  the front of a ship : Wedge
• the fan blades : Wedge
•  a toilet paper dispenser : Wheel
•  a door knob : Axel
•  a broom : Lever

 9.  Find out the MACHINES that these objects got:

•  Stapler: a) Lever b) Axel
• Wheel barrow:  a)Lever b)Wheel

 10.- What category do the following levers belong to? 
a) Screwdriver used to open a can. 1st class
b) Fihsing pole. 3rd class
c) Bicycle brake. 2nd class
d) Balance.1st class
11.- The weight of a boy sitting on a see-saw(balancín) 1m from the fulcrum generates a force of 440N. How much force must his little sister produce if she sits 2m from the fulcrum?.
220N.
12.- A force o 5000N is requiered to lift a stone. However, if a 2m lever is available and it is placed with the fulcrum 25m from the stone, how much force must be applied to the lever. 
400N
VIDEO ACTIVITY: "LEVERS".

• a) Write in one sentence what the teacher in the video is trying to explain.
• Simple machines help us to make our cotidian life things.
• b) What are the simplest of all machines based on?
• On the lever.
• c)What type of work is put in a machine?
• Energy.
• d) Archimedes said: “Give me a fulcrum and I will move the Earth”
• e) Which force is bigger in a lever?
• The load.

VIDEO TRANSCRIPT: "Chinese Bridge".

http://video.nationalgeographic.com/video/national-geographic-channel/specials-1/science-technology/ngc-chinese-bridge/

"They will base as much of their bridge on land as they can. Only one design can leap the nearly mile-long distance and keep the towers near shore: a suspension bridge. 

The Runyang, like every modern suspension bridge, relies on two main cables that stretch from one shore to the other.

At each end the yard-thick cables are rigidly anchored. But everywhere else the main cables can and do move, even across the top of the towers.

The towers are like tentpoles. They prop up the cables but the cables just drape over them.

If the main cables were anchored to the tower tops, the towers could not withstand the pulling forces. They would tumble inward and the entire structure would be lost.

Hanging down from the main cables are 360 suspender cables. These slim cables hold the road spans.

Even these joints are made to move. This flexibility can help the bridge survive extreme poundings from earthquakes and typhoons.

If the Runyang can be built as designed, it will be the world’s third longest suspension bridge.

It will have towers that soar seventy stories and a span that stretches nine-tenths of a mile.

Only one tower will sit  in the Yangtze River"

ACTIVITIES:
1.- To be able to adjust to different slopes and speeds may bicycles have multiple gears.
  a) How many different combinations can be used (teeth). (Cassett/Chainring) (pinón/plato).

Chainring\Cassett_____ XL - L - M - S.
  Larger_____________: XL-XL
  Smaller____________: S-S

  b) If the rider goes to 5rpm with the pedals. What speed takes the biky.
2.- The pulley for a washing machine drum measures 45cm. in diameter and the motor´s pulley is 9cm. Calculate the gear ratio and the drum´s speed when the motor is turning at 450rpm.
2250rpm3.- A mechanism is which the drive gear turns at 200rpm and the driven gear turns at 50rpm:
 a) What is the gear ratio. 4
 b) Is the drive gear has 20 teeth, how much has the driven gear. 5
4.- A force of 300N is required to lift a stone. 
 a) How much force must be applicaed, if you have a lever with the fulcrum situated at 1m of the stone.
60N                             


EXERCICIES:
A) LEVERS1. 
B) LEVERS2.