ESO 2

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.

What type of motion is it?

Linear motion

Oscillating motion

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.

Activity

Identify the input force and themechanisms used to transmit or transformmotion to the receptor.

MECHANISMS

In short, the purpose of mechanisms is totransmit and/or transform motion.

MOTION IS TRANSMITED MOTION IS

TRANSFORMED

CLASSIFICATION OF MECHANISMS

MECHANISMS

TRANSMISSION OF MOTION

LINEAR TRANSMISION

ROTARY TRANSMISION

TRANSFORMATION OF MOTION

ROTARY-LINEAR

RECIPROCATING ROTARY-LINEAR

LINEAR TRANSMISSION OF MOTION

LINEAR TRANSMISSION

Input force → produces a linear motion

The motion transmitted to the receptoris also linear

Linear transmission

LEVER

THE LEVERThe lever consists of a bar (rigid) whichpivots on a support point (fulcrum). Using a lever, heavy objects can be liftedwith little force.

THE LEVERLevers are classified into three types:

Why is this a class 1 lever?

Why is thisa class 2 lever?

Why is this a class 3 lever?

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

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

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

Linear transmission

PULLEY

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.

Types of pulleys

•Fixed pulleyFixed pulleys havetheir center pointfixed.

The fixed pulleychanges the directionof the force.

F = RF = ??

R = 10 kg

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 = ?

Exercise

What effort do you need to lift a load of 300 N?

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?

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

Are these pulleys turning clockwise or anti-clockwise?

Driver pulley

PULLEYS WITH BELTUSES

Washing machine

Motion is transmittedfrom the motor tothe drum.

Can you identify thedriver and the driven

pulleys?

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

• Everyone has used a bicycle and noticed that it is driven by a large driver gear wheel with pedals attached.

3. INTERLOCKING GEARS

• The direction of rotation is reversed.

• They must be close to one another.

• 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

Are these gears turningclockwise or anticlockwise?

INTERLOKING GEARSUSES

TEXTILE MACHINE

CLOCK

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.

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.

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.

WORM DRIVE – USESUSES

• For tuning the strings of a guitar

• Speed reducing systems

MECHANISMS THAT REDUCE OR INCREASE SPEED

Smallwheelsturn

fasterthan bigwheels

Activity – Is speed increasedor reduced?

ROTARY – LINEAR WHEEL RACK AND

PINIONNUT AND BOLT WINCH AND

CRANK

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.

• A good example of a ‘rack and pinion’ gear system can be seen on trains that are designed to travel up steep inclines.

Sliding doors sometimes use rack and pinion mechanisms

ROTARY - LINEARWHEEL RACK AND

PINIONNUT AND BOLT WINCH AND

CRANK

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.

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.