presentación de powerpoint...pivots on a support point (fulcrum). using a lever, heavy objects can...
TRANSCRIPT
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ESO 2
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MOTIONThere are four basic types of motion:• Linear motion is moving in a straight
line, such as on a paper trimmer.• Rotary motion is turning round in a
circle, such as a wheel turning.• Reciprocating motion is moving
backwards and forwards in a straight line, as in cutting with a saw.
• Oscillating motion is swinging from side to side, like a pendulum in a clock.
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What type of motion is it?
Linear motion
Oscillating motion
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WHAT IS A MECHANISM?
•An input force → our muscles, an animal, aspring, a river, an electric motor……
•The output receptor finally performs the work.
Mechanisms transmit and transform force and motion from an input source to an output receptor.
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Activity
Identify the input force and themechanisms used to transmit or transformmotion to the receptor.
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MECHANISMS
In short, the purpose of mechanisms is totransmit and/or transform motion.
MOTION IS TRANSMITED MOTION IS
TRANSFORMED
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CLASSIFICATION OF MECHANISMS
MECHANISMS
TRANSMISSION OF MOTION
LINEAR TRANSMISION
ROTARY TRANSMISION
TRANSFORMATION OF MOTION
ROTARY-LINEAR
RECIPROCATING ROTARY-LINEAR
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LINEAR TRANSMISSION OF MOTION
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LINEAR TRANSMISSION
Input force → produces a linear motion
The motion transmitted to the receptoris also linear
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Linear transmission
LEVER
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THE LEVERThe lever consists of a bar (rigid) whichpivots on a support point (fulcrum). Using a lever, heavy objects can be liftedwith little force.
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THE LEVERLevers are classified into three types:
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Why is this a class 1 lever?
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Why is thisa class 2 lever?
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Why is this a class 3 lever?
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THE LAW OF THE LEVER
The law of the lever states that when a lever isbalanced, the effort (F) multiplied by its distance from the fulcrum (BF) equals the load (R) multiplied by its distance from the fulcrum (BR). This law of equilibrium is true for all classes of levers.
F * d = R * rd r
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ACTIVITY
The boy (50kg) is 0,5m from thefulcrum.How far from the fulcrum is hissister if the seesaw is balanced? His sister weighs 25kg.
d r
F * d = R * r
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HOMEWORK
2. A boy who weighs 30 kg sits on one end of a seesaw. On the otherend there is a girl who weighs 20 kg. The girl is 1.5m from thefulcrum.
a. How far from the fulcrum must the boy sit in order to balancethe seesaw?
b. If the girl is now 3m from the fulcrum, where should the boysit to balance the seesaw?
c. What conclusion can you make about the seesaw?
1. Locate the fulcrum,force and resistancein the levers below.Identify each type oflever
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Linear transmission
PULLEY
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THE PULLEY
The pulley is a wheel that rotatesaround an axis. The wheel has a groove.A rope is passed around the outside of the wheel.The object to be moved is attached toone end and the force is applied on theother end.
The pulley makes it easier to lift a weight because you can use the weight
of your whole body.
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Types of pulleys
•Fixed pulleyFixed pulleys havetheir center pointfixed.
The fixed pulleychanges the directionof the force.
F = RF = ??
R = 10 kg
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Types of pulleys
•Movable pulleyCombined pulleys are a combination of fixedand moveable pulleys.
Moveable pulleys are free to move up and down.
F = R/2
R = 10kg
F = ?
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Exercise
What effort do you need to lift a load of 300 N?
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HOMEWORK
1. What mechanism is the boy using? How does it help him get water?
2. What effort do you need to lift a load of 300 N with a fixed pulley? And with a moveable pulley? Draw both types of pulleys.
3. What effort do you need to lift a load of 80 kgf with a fixed pulley? And with a moveable pulley?
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1. PULLEYS WITH BELTS
They are pulleys joined through a rope, called belt.The belt transmits the motion from the driver pulley to driven pulley.Both pulleys turn in the same direction (unless the belt is crossed).
http://actividadespdi.wikispaces.com/pulleys+with+belts
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Are these pulleys turning clockwise or anti-clockwise?
Driver pulley
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PULLEYS WITH BELTUSES
Washing machine
Motion is transmittedfrom the motor tothe drum.
Can you identify thedriver and the driven
pulleys?
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2. GEARS WITH CHAIN
• They are gears joined through a chain.
• The chain transmits the motion from the driver gear to driven gear.
• Both gears turn in the same direction.
link
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• Everyone has used a bicycle and noticed that it is driven by a large driver gear wheel with pedals attached.
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3. INTERLOCKING GEARS
• The direction of rotation is reversed.
• They must be close to one another.
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• Gear ‘A’ is called the ‘driver’ because this is turned by a motor.
• As gear ‘A’ turns it meshes with gear ‘B’ and it begins to turn as well. Gear ‘B’ is called the ‘driven’ gear.
MOTOR
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Are these gears turningclockwise or anticlockwise?
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INTERLOKING GEARSUSES
TEXTILE MACHINE
CLOCK
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4. FRICTION WHEELS
They are wheels joined through friction.The driver wheel transmits motion to the driven wheel by rolling.
Both wheels turn in opposite directions.
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HOMEWORK1. List everyday machines that use pulleys with belts
or gears.
2. In your notebook, draw diagrams for the 3 types oflever.
As usual, do yourhomework on
your notebook.
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WORM DRIVE• It’s comprised of a screw (worm) an a
cogwheel (wormgear).
• Motion can only be transmitted from the screw to the cogwheel.
• It is used to reduce speed.
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WORM DRIVE – USESUSES
• For tuning the strings of a guitar
• Speed reducing systems
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MECHANISMS THAT REDUCE OR INCREASE SPEED
Smallwheelsturn
fasterthan bigwheels
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Activity – Is speed increasedor reduced?
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ROTARY – LINEAR WHEEL RACK AND
PINIONNUT AND BOLT WINCH AND
CRANK
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RACK AND PINION• Transforms circular
motion into straight motion and vice versa.
• It consists of a toothed bar which engages a cogwheel.
• This mechanism is reversible since the drive element can be wither the rack or the pinion.
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• A good example of a ‘rack and pinion’ gear system can be seen on trains that are designed to travel up steep inclines.
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Sliding doors sometimes use rack and pinion mechanisms
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ROTARY - LINEARWHEEL RACK AND
PINIONNUT AND BOLT WINCH AND
CRANK
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CAM and FOLLOWERIt consists of:•A disk (cam) which turnseccentrecally (the rotatingshaft is off-centre )•The follower is a rod which isallways in contact with the disk
It transforms circular motioninto alternating linear motion(moves up and down).
Motion can only be transmittedfrom the cam to the follower.
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ROD AND CRANK •The crank moves in a circular motion
•One side of the rod moves back and forth while the other moves in a circle.
•It transforms circular motion into alternating linear motion and viceversa.