MECHANISMS AND SIMPLE MACHINES

TECHNOLOGIES - 3º ESO

Name: ________________________________________________ Class:______

MECHANISMS

INTERESTING WEB SITES

http://www.technologystudent.com/cams/camdex.htm

http://www.youtube.com/watch?v=eAniA73C6WI (washing machine museum)

MAIN VOCABULARY

MAIN VOCABULARY OF THE UNIT

ENG SP ENG SP

Force To spin

Effort Axle

Load Shaft

Resistance Gear

Movement Transmission

Motion

Rotary

Linear

1. MAIN MECHANISM CLASSIFICATION

Mechanisms are simple machines that transform an allow objects to move or to transmit the motion

from one part of a machine to another one.

They can change the speed, the direction, the force or the type of movement.

A few examples:

A lift needs to go up and down, but the motor that moves the lift has a rotary motion. Between

the motor and the cabin there is a mechanism that transforms the rotary movement of the

electric motor into a linear up and down movement. Besides, the electric motor spins very

quickly and the mechanism has to reduce the speed so that the lift moves at a reasonable

speed.

o The mechanism reduces the speed but increases the force. Thanks to that, the lift can

move a big load with a relatively small motor.

Modern bikes use a gear set to change the speed of it using a gear-chain system.

Cranes lift heavy loads with reasonable powered motors. They do it thanks to a mechanism.

As a first classification, we can see the mechanisms as:

Linear transmission Mechanisms:

They transmit the movement from a part to another but always linear. Ex: levers, pulleys.

Circular transmission mechanisms.

They do the same of the ones above but in this case the movement is circular. Ex.: pulleys and belts,

friction pulleys, gears ...

Circular movement transformation to linear

One part of the machine produces rotary movement and it is transformed into circular in another part

of it. Ex.: Rack and pinion, nut and screw, winch.

Circular movement transformation to alternative linear. Ex. Crank-connecting rod system,

crankshafts, cams, eccentrics

All the mechanisms have in common that they are used to move a load (carga o resistencia) by means of

an effort (potencia), the force exerted by the user, a motor or an engine.

All the mechanisms have in common as well that when they have a mechanical advantage, they do it at

expense of the speed and vice versa. For instance when riding a bike, if we have to climb a slope, we

must choose the gear to easy the movement of the pedals but in exchange we’ll have to move them

fast.

2. LINEAR TRANSMISSION MECHANISMS

They transmit the movement or motion in a linear way. They are levers, the pulleys, fixed and moving

and the block and tackle. Lets know more about them.

2.1. LEVERS.

A basic one is a bar of wood or metal which pivots around a fixed point called the fulcrum or pivot

(fulcro o punto de apoyo). And the clearest example we can see is the see-saw (columpio de barra y

asientos) of a playground. In this case everyone knows that the swing doesn’t balance when different

weights are on each seat, but we also know that the balance is possible if we move the louder weight

towards the fulcrum.

The main parts of the lever are:

The load “L” (carga o Resistencia “R”): is the weight we have to lift.

Effort is the force exerted by the user.

The effort arm “Ea”(brazo de potencia Bp o Lp): the distance between the effort application point and

the fulcrum.

The load arm “La”(brazo de resistencia Br o Lr): the distance between the load application point and the

fulcrum.

So levers balance equation is:

Usually we employ Newton or Kilos as the unit for forces (effort and load) and metres, cm or millimetres

for the arms, but we have to pay attention to apply always the same units.

In all levers, if the effort arm is longer than the load arm, we’ve got mechanical advantage. That means

that it amplifies the force exerted by the user, so that the force needed to lift the load is smaller than

the weight of that load. In exchange, the speed and then the movement of the effort have to be higher

than the one of the load (and with the same ratio of the mechanical advantage).

2.1.1. TYPES OF LEVERS

2.1.1.1. FIST-CLASS LEVER OR CLASS 1 LEVER(PALANCA DE 1ER GRADO)

In this lever the fulcrum is placed always in the middle, this is between the load and de effort. Examples:

The see-saw, the weighing scales...

2.1.1.2. SECOND-CLASS LEVER OR CLASS 2 LEVER(PALANCA DE 2º GRADO)

In this lever the fulcrum is placed at one end of the bar, the effort is applied at the other end and the

load in the middle of them.

Effort Arm

Load Arm

Effort

Load

Fulcrum

Examples are: the wheelbarrow, the bottle opener, the nutcracker, a pair of scissors...

With this lever we always get mechanical advantage as the Effor Arm is longer than the Load Arm.

Palancas de segunda clase

2.1.1.3. THIRD-CLASS LEVER OR CLASS 3 LEVER(PALANCA DE 3º GRADO)

In this lever the fulcrum is placed at one end of the bar, the load is applied at the other end and the

effort in the middle of them. With this kind of lever no mechanical advantage is obtained as the Effort

Arm is shorter than the Load Arm. Instead we gain in speed of the load or movement of it.

Examples: the shovel (pala para cavar), the human mandible /’mandibl/, a rod, a broom, ...

Effort Arm

Load Arm

Effort

Load

Effort Arm

Load Arm

Effort

Load

Palancas de tercera clase

LEVER EXERCISES

1. To raise a load of 50 kg we have a lever whose bar is 2.5 m length. The Load arm is 0,50 m and

the effort arm is 2 m. Find out the force we have to apply. Draw a sketch of it.

2. A see-saw of a play ground has a bar of 4 metres. Two children are playing with it. One of the

children weighs 50 kg and the other one 40 kg. If the 40 kg boy is sitting on one seat (2 metres

from the fulcrum), calculate the distance from the fulcrum the other boy has to seat down to

balance the see-saw. Draw a sketch of it.

3. In one first class lever we have to lift a weight of 100 kg. The resistance arm is 1 meter length,

and the effort arm is 3 metres length. How many kg have we to apply to lift the resistance?.

Draw a sketch of it.

4. A wheelbarrow has its bin at 0.5 metres from the axle of the wheel. The handle is at 1.25 metres

from this axle. Calculate the force a worker has to do to lift a 50 Kg load. Draw the sketch of this

lever.

5. In the digger of the picture, identify the all the levers it has got and their class.

6. Complete the table below.

TOOL ENGLISH NAME

SPANISH NAME

LEVER CLASS

TOOL ENGLISH NAME

SPANISH NAME

LEVER CLASS

2.2. PULLEYS

A pulley is also called a sheave or drum and is a wheel which has a groove (canal) between two flanges

(rebordes) around its circumference. The pulley turns around a fixed axle. The drive element of a pulley

system can be a rope, cable, belt, or chain that runs over the pulley inside the groove.

In fact, the pulley is only used to avoid friction between the rope and the point the cable slides.

A simple pulley does not increase the speed of the rope nor reduce the effort needed to move a load.

The only advantage is to reduce friction and change the direction of the rope to be more ergonomic

(easier to handle by a person). For instance to lift a load without help we must use our muscles to do all

the work. If we use a pulley hanging from the ceiling and a rope, we just grip the rope and use our

weight to lift the same load.

As we are going to see below, the way we use pulleys can help us to do a work, thus providing mechanic

advantage. But like in all machines, the mechanical advantage supposes to change force for distance.

That means, for instance, that if we have to move a load and we do half and the force of that load

weights, then we’ll have to pull the rope two times the distance the load is going to move.

2.2.1. FIXED PULLEYS (POLEA FIJA)

It doesn’t have mechanical advantage, they only changes the direction in which we have to pull to lift

the load. They are usually used in lifts, where a counterweight is installed to help to lift the cabin.

F=L

As there’s not mechanical advantage, we’ll have to pull the rope the same distance the load is going to

move.

2.2.2. MOVABLE PULLEY (POLEA MÓVIL)

It is a normal pulley but in this case the load is hanging from its axle as follows.

With this system we get mechanical advantage because the load is hanging from two parts of rope and

we just pull on one of them, the other one is tied to a fixed point.

The mechanical advantage here is 2 and of course, we’ll have to pull the rope two metres if we want to

lift the load 1 meter.

2.2.3. Block and tackle.

Usually, the moving pulley is used in combination with another fixed to get the advantages of both of

them. This mechanism is called block and tackle.

Gun and tackle (polipasto sencillo)

Consider the set of pulleys that form the moving block and the parts of the rope supporting this block. If

there are “n” of these parts of the rope supporting the load “R”, then a force balance on the moving

block shows that the tension in each of the parts of the rope must be R/n. This means the input force on

the rope is T=R/n. Thus, the block and tackle reduces the input force by the factor n. As each moving

pulley in the moving block is hanging from two parts “n” of rope, then we can write the equation like

this

Where n= number of moving pulleys.

Nevertheless as we can guess, if we have to lift the load 1 meter we’ll have to pull the rope “n” times

metres.

So for the double tackle is going to be:

F=R/2n

Examples of use are: the lifts and cranes.

PULLEYS EXERCISES.

1. Considering the pulley below. Calculate the force we have to exert to lift the load of 50 Kg. How

many metres do we have to pull the rope to raise the load 2 metres?.

2. Considering the pulley below. Calculate the force we have to exert to lift the load of 50 Kg. To

raise 3 metres the load, how many metres do we have to pull the rope?

R/2 R/2 R/2 R/2 R/2

R

3. Considering the gun and tackle below. Calculate the force we have to exert to lift the load of 50

Kg. Why this pulley system is better than the one of the exercise 2?. How many metres do we

have to pull the rope if the load is going up 3 metres?.

4. With our hands and the help of some pulleys and a rope, we have to lift a 60 kg weight load to a

height of 4 metres. The maximum force we can exert is 20 kg. Draw the diagram to easy the

work. How many metres of rope do we have to pull to lift the load 20 metres?.

5. The lifts of the Eiffel tower is operated by means of a counterweight. When the counterweight

drops the lift cabin goes up, but while the height from where the counterweight drops is only 20

metres, the lift cabin has to go up 80 metres. Design a pulley system to solve this problem. Draw

the diagram.

3. CIRCULAR TRANSMISSION MECHANISMS

They transmit the circular motion from an input shaft to another. Examples can be: friction wheels, belt

and wheel (or pulleys), gears systems and the worm gear.

3.1. FRICTION WHEELS

Friction wheel

Driver wheel (rueda o polea motriz) it is the wheel moved directly by a motor or engine.

Driven wheel (rueda conducida) it is the one to which the motion is transmitted.

The motion to the driven wheel is transmitted by means of friction existing in the contact of both

wheels. Consequently, both wheels rotate in opposite direction.

This allows for mechanical power, torque, and speed to be transmitted across axles. If the pulleys are of

differing diameters, a mechanical advantage is realized.

Notice that always the smallest wheel spins the fastest. In exchange its torque (rotary strength) is the

lowest. To calculate the speed of the driven wheel we employ the equation:

Where

D1 = diameter of the driver wheel.

D2 = diameter of the driven wheel.

N1 = speed of the driver wheel or output speed (usually in rpm revolutions per minute (revoluciones por

minute)).

N2 = speed of the driven wheel or input speed.

The same results are been obtained if change the diameters for the radiuses /‘reɪdɪəsəs/

This mechanism is reversible that means that we can use both wheels as driven or driving wheels.

The speed ratio between the driver and driver wheel is calculated as follows:

Transmission ratio = Output speed/Input speed

This equation can be used for all the circular transmission mechanisms

FRICTION WHEELS EXERCISES

1. In a friction wheel mechanism, the driving wheel rotation speed is 5000 rpm. Figure out the

rotation speed of the driven wheel if the diameters are the following ones: 10 cm for the driver

wheel and 5 cm for the driven wheel. Draw the diagram.

2. Calculate the diameter of a driven wheel in a friction wheel transmission system if its rotation

speed is 3000 rpm. The driver wheel rotates at a speed of 500 rpm and its diameter is 15 cm.

Draw the diagram.

3.2. BELTS AND PULLEYS SYSTEMS

It is use to transmit motion between two parallel axles.

Belt and pulley

A Belt passes around two pulleys wheels. Then when the driver pulley moves, it moves the belt and the

belt moves the driven pulley. Both pulleys wheels rotate in the same direction.

The transmission speed ratio is the same as in the friction wheels. So the equation is exactly the same:

Where

D1 = diameter of the driver wheel.

D2 = diameter of the driven wheel.

N1 = speed of the driver wheel (usually in rpm revolutions per minute (revoluciones por minute)).

N2 = speed of the driven wheel.

This system is widely used in washing machines, pillars drills, cars etc.

In this type of mechanism slipping may be a problem (or not). To avoid slipping, toothed pulleys and

belts are used.

Toothed belt and toothed pulleys

This mechanism is reversible that means that we can use both wheels as driven or as driving wheels.

PULLEYS AND BELTS EXERCISES:

Fill the table with the speed rotation of the chuck of a pillar drill whose internal transmission system has

two cone pulleys joined by a belt as shown in the picture. Calculate all the possibilities considering the

motor which moves the driver pulley rotates at 2300 rpm. (note: all the diameters are in mm)

Pulleys joined DRIVEN SPINNING SPEED

1 gear 45-115

2 gear 70-90

3 gear 95-65

4 gear 120-40

3.3. GEARS (ENGRANAJES)

Gears are toothed wheels that mesh each other to transmit the circular motion or to change the speed

between two axles, force direction. The teeth of the gears must be identical.

The gears rotate in opposite direction. The speed of the driven gear (gear ratio) depends on the number

of teeth ratio between the two gears

Where

Z1 = diameter of the driver wheel.

Z2 = diameter of the driven wheel.

N1 = speed of the driver wheel (usually in rpm revolutions per minute (revoluciones por minute)).

N2 = speed of the driven wheel.

Sometimes the driver gear is called pinion.

3.3.1. SPUR GEAR (ENGRANAJES CILINDRICOS)

They are the most common type of gears. With high speed, noise can be a problem.

The smaller the gear (with fewer teeth), the higher the speed (see the equation showed before).

No possibility of slipping with this mechanism, so great strengths can be transmitted

Idler gear

The gears rotate in opposite direction. If we need them to rotate in the same direction, an idle gear

(engranaje loco) should be used. With the idler gear, the speed transmission is not affected.

Idler gear

They are commonly used in gear boxes in cars and other machines.

Spurs gears are reversible that means that we can use both gears as driven or as driving gears.

http://www3.ul.ie/tilde_accs/nolk/www/gears.htm

3.3.2. COMPOUND GEAR TRAINS

A compound gear trains well have at least two gears attached to one of the shafts, and can achieve large

changes in speed of rotation.

http://www.technologystudent.com/gears1/gears3.htm

Compound gear train

For the speed transmission ratio we use the same equation we’ve seen for the spur gears, but we have

to apply it step by step and considering that the speed calculated for gear 2 is the same as the gear 3 as

they are the same part.

3.3.3. BEVEL GEARS

These gears have teeth cut on a cone instead of a cylinder blank. They are used in pairs to transmit

rotary motion and torque where the bevel gear shafts are at right angles (90 degrees) to each other. An

example of two bevel gears is shown below.

Bevel gears

For the speed transmission we use the same equation we know from spur gears.

Bevel gears are reversible as well. It doesn’t matter what the input gear is that the mechanism will work

properly.

3.3.4. WORM GEAR (TORNILLO SIN FIN)

It is constituted by a screw (worm) and a spur gear. As the worm turns then it pulls the gear. Worm

gears have a great speed reduction ratio, so they are used when you want to slow down a movement

considerably. Also the two axles (the one of the worm and conic gear) are 90º.

Worm and gear

For the speed transmission we use the same equation seen for spur gears considering that the worm is

a gear with only one teeth (Z=1). So:

This mechanism is not reversible. The only driver gear has to be always the worm and the driven gear

has to be the driven one.

Worm drives are used in presses, in rolling mills, and on rudders /timón/. Worm gears are used on many

lifts (in US English known as elevator) and escalator-drive applications due to their compact size and the

non-reversibility of the gear.

3.4. CHAINS AND SPROCKETS (SISTEMA DE PIÑONES Y CADENA)

It is a system similar to the belts and pulleys but built in toothed wheels and a chain. The driver toothed

wheel meshes with the chain and pulls it as it rotates. The chain is in tension with the driven tooth

wheel which meshes as well with it. As the chain moves, the driven wheel turns.

Chain and sprocket

Bicycles and motorbikes use sprockets and chains because of their greater strength and the fact that

they do not slip.

The speed ratio is the same as with the spur gears.

As well as the spur gears It is a reversible mechanism.

GEAR VERSUS PULLEYS: ADVANTAGES AND DISADVANTAGES

Although we may think that the gears are more powerful than the pulleys thus better, the fact is that

there is not a system better than the other. The use of each type of mechanism depends on the result

we want to obtain. The main features of them are:

Advantages of belts and pulleys over the gears:

Belts are much quieter then metal gears (it is widely used in cars).

Belts and pulleys do not need to be lubricated.

Belts allow some fitting tolerance.

Flat belts allow some slippage /’slɪpɪdʒ/ as a matter of safety (used in pillar drills)

Easy replacement.

Disadvantages of belts and pulleys:

They can slip (although not the toothed ones)

Can only be uses in clean/dry conditions.

Advantages of gears and chains over pulleys and belts

Large forces can be transmitted.

They do not slip.

They can be used in tough conditions of dampness and dirt accumulation.

Disadvantages of belts and pulleys:

They are noisy.

The maintenance is not so easy than the pulleys and belts.

They need lubrication.

3.4.1. BELTS AND PULLEYS ASSEMBLIES (TREN DE POLEAS Y CORREA).

When the reduction of speed of the driven belt cannot be achieved, then a compound system of pulleys

and belts can be used.

This consists of two pairs of belts and pulleys working together. As shown in the picture, the central

pulley is made up with two pulleys built together. To study this mechanism we have to divide it in parts.

First of all we analyze the first two pulleys and then the other two, considering the same speed for both

central pulleys.

Pulleys 1 and 2

Pulleys 3 and 4 (considering N2=N3)

4. LINEAR INTO CIRCULAR TRANSMISSION SYSTEMS

4.1. RACK AND PINION SYSTEM

A rack and pinion is a type of linear actuator that has a pair of gears which convert rotational motion

into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the

rack"; rotational motion applied to the pinion causes the rack to move, thereby translating the

rotational motion of the pinion into the linear motion of the rack.

This system is reversible. That means that either we can introduce the rotational movement in the

pinion to obtain a linear movement in the rack or vice versa: to introduce the linear movement in the

rack to obtain the circular movement in the pinion.

4.2. NUT/SCREW TRANSMISSION SYSTEM.

Screw/Nut mechanism is a widespread technique to move loads. In we turn the screw while locking the

nut, then the nut will move back or forth depending on the turning direction of the screw.

This mechanism has a low transmission ratio. This is that a fast movement of the screw, results in a slow

linear movement of the nut.

4.3. THE WHINCH

A winch is a mechanical device that is used to pull in (wind up) or let out (wind out) or otherwise adjust

the "tension" of a rope or wire rope (also called "cable" or "wire cable"). In its simplest form it consists

of a spool and attached hand crank. It is the system used to lift buckets in water wells or in fishing rods

The balance law is the same as in the levers, considering the length of the crank as the Effort arm and

the radium of the spool as the Load arm

4.4. CIRCULAR TO ALTERNATIVE LINEAR MOVEMENT TRANSMISSION

We introduce rotary movement and we obtain alternative linear movement.

4.4.1. CRANCK-ROD SISTEM

It transforms rotary movement into alternative linear movement or vice versa (it’s a reversible

mechanism).

4.4.2. CAM OR ECCENTIRCS AND FOLLOWER

The cam and follower is a device which can convert rotary motion into linear motion (movement in a

straight line). A cam is a specially shaped piece of material, usually metal or hard wearing plastic, which

Effort arm

Load arm

Effort

Load

is fixed to rotating shaft. The cam can have various shapes e.g.. round, oval, heart shaped. A follower is a

mechanism which is designed to move up and down as it follows the edge of the cam.

This system is quite easy to use.

5. BEARINGS

A bearing is a machine element that constrains relative motion and reduces friction between moving

parts to only the desired motion. They are used in machines axis.

The term "bearing" is derived from the verb "to bear", a bearing is a machine element that allows one

part to bear (to support) another one.

3ºE.S.O. BILINGUAL TECHNOLOGY

I.E.S. PABLO NERUDA CURSO 2013-2014

UNIT 5.- MECHANISMS

Page 1

1. Do you know that there are a lot of levers in all our

body?. Here are shown some of them. Write down

where the force, resistance and fulcrum are and

identify each class:

2. We want to carry two 50 kgs packets of cement with the wheelbarrow shown in the drawing. a) Indicate the type of lever b) Calculate the force we need to apply to lift the weight up.

3. In the next sketches, each blue square weights 2kg. and each segment is 1 m.long. It is required

determining whether they are in equilibrium (balanced), if not which way they will incline.

WDriving=WResistance

F·d=R·r 2 kg ·3m=2kg·2m

6>4 so it’ll turn to the left. .

Example:

F R

r d

1 2 3

4 5 6

3ºE.S.O. BILINGUAL TECHNOLOGY I.E.S. PABLO NERUDA CURSO 2013-2014

UNIT 5.- MECHANISMS

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4. Figure out the force needed to move a 100kg object with a first class lever by knowing the resistance and force arms are 50 cm and 150 cm, respectively 6. How much strength will be necessary to apply in order to lift a 90 kg rock with the lever shown on the drawing? What class is it? 8. Look at the levers shown on the pictures: a)What class are they? b)Which one will allow us to make less effort? Why? (Note: If you don’t know how to solve it you can use any value for “R”,”r” and “a”. Then calculate the force in both cases.) 9. Using the pliers shown in the photo, we want to cut a wire that resists a 2 Kg force. Answer these questions: a) What type does the lever belong? b) Calculate the force that will be necessary for cutting it?.

5. Calculate the length of the resistance arm in a second class lever by knowing we need to apply a 40 kg force to move a 120 kg object. The resistance arm is 15cm long. 7. Answer these questions: When will the needed force in a first class lever be lower than the resistance?

Never.

Ever.

When the resistance arm is longer than the arm of the force.(r>d).

When the force arm is longer than the resistance arm(r<d).

When will the needed force in a second class lever be lower than the resistance?

Never.

Ever.

When the resistance arm is longer than the arm of the force.(r>d).

When the force arm is longer than the resistance arm(r<d).

When will the needed force in a third class lever be lower than the resistance?

Never.

Ever

When the resistance arm is longer than the arm of the force.(r>d).

When the force arm is longer than the resistance arm(r<d).

In order to perform the minimum effort in a first and second class lever, the fulcrum should be placed…

Far away from the resistance.

Close to the resistance.

At one end of the lever.

In the center of the lever. When will ever the force be bigger than the resistance?

In a first class lever.

In a second class lever.

In a third class lever.

It will always happen in the third class and sometimes in the first class.

3ºE.S.O. BILINGUAL TECHNOLOGY

I.E.S. PABLO NERUDA CURSO 2013-2014

UNIT 5.- MECHANISMS

Page 3

10. Look at the next drawings of levers and point out where the force, the resistance and the fulcrum are.

Finally identify each class.

Example:

R

F

Fulcrum

1st Class 1 2 3 4 5 6

7 8 9 10 11 12

13 14 15 16 17 18

19 20 21 22 23 24

25 26 27 28 29 30

3ºE.S.O. BILINGUAL TECHNOLOGY I.E.S. PABLO NERUDA CURSO 2013-2014

UNIT 5.- MECHANISMS

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11. Calculate the minimum effort force we should perform to lift a 80N load up with the following pulleys. Write down the type in each case.

12. Look at the pulleys shown in these drawings.

Which one requires the least force to move?

A

B

C

We’ll perform the same effort in all of them. 13. Looking at the drawing, what will be the effort we have to perform if the load is 3200 N?

200 N

400 N

800 N

1600 N

3200 N

More than 3200 N

14. The effort needed in the following pulley with a 1000N load will be:

200 N

250 N

500 N

750 N

1000 N

More than 1000 N

15. How much force is required to move a 100N weight in each case? (Note: Look at the length of the rope that is necessary to pull in each case for lifting the weight the same height)

3ºE.S.O. BILINGUAL TECHNOLOGY

I.E.S. PABLO NERUDA CURSO 2013-2014

UNIT 5.- MECHANISMS

Page 5

16. How much force will a 800kg car have to perform to get out the garage considering the inclined plane shown in the picture?

17. A train full of people in a roller coaster is trying to go uphill. Its weight is 4500N and the ramp has a 40% inclination. How much force is required to get it? 18. Look at this system with gears: a) How many gears will rotate anti-clockwise when gear A turns? b) What will the rotation direction in gears K,L,H & G be?

19.Here you have several rotatory transmitting motion mechanisms. It’s required to point out the rotation direction in each pulley and indicate whether the global system is a multiplying (+), reducing (-) or constant (=) system.

10m

2m

Example:

(=) It’s a constant system Velocity remains constant

1

2 3

4 5

6 7

8

9

10

3ºE.S.O. BILINGUAL TECHNOLOGY I.E.S. PABLO NERUDA CURSO 2013-2014

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20. This drawing shows a pulley trains with belt , where X is the primary drive wheel:

a) How many wheels will rotate when pulley X turns?

b) What rotation direction will pulleys D and F have?

c) If all wheels have the same size and wheel X turns at 20 rpm (revolution per minute), What will be the speed in wheel B?

d) What will happen if we join wheels B & D with a belt? And if we do the same with pulleys E & F instead?

21. Calculate the speed of the driven wheel (rueda conducida) (1) shown in this skecth as well as the gear ratio. Finally indicate the type of system (Multiplying-Reducing-Constant)

d1= 20 cm d2= 30 cm n2= 1200 rpm

22. In the diagram below the bigger cogwheel has 40 teeth, whereas the pinion 20.

a) Calculate the gear ratio. b) At what velocity will the pinion rotate if the other moves at 300 rpm?

23. The diagram below shows a pulley trains with belt, where we want to know: a) Which direction will each pulley move? (the same or the opposite to the engine). Indicate them by using an arrow b) What speed will each pulley have? Just use this symbols (+) multiplying (-) reducing (=) constant

24. The engine that is shown in this picture spins in the rotation direction pointed out by the arrow.

a) Which rotation direction will pulley “A”have?

Equal to the engine

Opposite to the engine

b) The velocity in wheel A will be....

Faster than the engine

Slower than the engine

Just the same as the engine

Zero. c) If the engine rotates at 40 rpm and the size of pulleys are the ones shown on the table, What will the speed of wheel A be?

Polea Diametro

A 10 cm B 20 cm C 10 cm D 20 cm

Driving wheel

C

D

Driven wheel

Example:

(+)

B

3ºE.S.O. BILINGUAL TECHNOLOGY

I.E.S. PABLO NERUDA CURSO 2013-2014

UNIT 5.- MECHANISMS

Page 7

25. In the following diagram, the crank handle turns as it’s shown.

a) Which direction will gear “A” move?

Anticlockwise Clockwise b) The speed of gear A will be....

Faster than the crank handle

Slower than the crank handle

Just the same.

Zero

a) Which direction will the wheel move?

Anticlockwise Clockwise b) The speed of the wheel will be....

Faster than the crank handle

Slower than the crank handle

Just the same.

zero

26. In the following diagram is shown the transmitting motion mechanism made of gears with chain of a car toy.

a) Which direction will the wheels move?

Just the same as the engine

Opposite to the engine b) The speed of the wheels will be....

Faster than the engine

Slower than the engine

Just the same.

zero

27. Look at the drawings below and answer the questions.

a) Indicate the direction of motion of each pulley/gear using arrows. b) Indicate whether the following statements are true “T” or false “F”:

Pulley “A” spins faster than pulley “B”.

Pulley “B” spins slower than gear “C”.

Pulley “B” and gear “C” spin at different speeds.

Gear “C” spins slower than pulley “A”.

Gear “D” spins faster than gear “C”.

a) Indicate the direction of motion of each pulley/gear using arrows. b) Indicate whether the following statements are true “T” or false “F”:

Gear “A” spins faster than gear “B”.

Pulley “C” spins faster than gear “D”.

Gear “B” and pulley “C” spin at the same speed.

Gear system “A-B” is a multiplying system.

Gear system “C-D” is a reducing system.

Gear system “A-B-C-D” is a reducing system.

a) At what velocity will gear “A” rotate?

Faster than the engine.

Slower than the engine.

At the same speed. b) So the system shown is a:

Reducing system.

Multiplying system.

Constant system.

1

2

1

Clockwise

2

Anticlockwise

3

3ºE.S.O. BILINGUAL TECHNOLOGY I.E.S. PABLO NERUDA CURSO 2013-2014

UNIT 5.- MECHANISMS

Page 8

28. The figure below shows a conical gear mechanism connected to an electrical engine.

a) What system is it?

A reducing system.

A multiplying system.

A constant system. b) Which direction will the conical gear “B” move?

Just the same as the engine

Opposite to the engine

29. The engine of a washing machine is connected to a 8cm diameter pulley whereas the tumble is joined to a 32cm diameter pulley. The fastest speed, the tumble spins, is 1200 rpm. What speed will the engine turn?

If we change the pulley of the engine with a double one bigger, what speed will the engine have?

30. The figure below shows the pulley trains with belt of a power drill. Depending on the pulleys combination we select, we can get different speeds in the drill bit. (broca)

a) Which combination of pulleys will allow us to get the slowest speed in the drill bit? b) Which combination of pulleys will allow us to get the fastest speed in the drill bit? c) If the engine spins at 1400 rpm, What’s the minimum speed the drill bit can rotate?

31. The gear ratio in a friction drive system is 2.5. Calculate the speed of the driving wheel by knowing the speed of the driven wheel is 250 rpm. Indicate the type of system (multiplying-reducing-constant).

3ºE.S.O. BILINGUAL TECHNOLOGY

I.E.S. PABLO NERUDA CURSO 2013-2014

UNIT 5.- MECHANISMS

Page 9

32. Calculate the gear ratio of the system and the speed of each pulley if the driving wheel (1) rotates at 100 rpm (clockwise).

d1= 10 cm d2= 20 cm d3= 15 cm d4= 30 cm

34. The bicycle shown on the picture below has 2 chain rings (platos) with 44 & 56 teeth and 5 cassettes (piñones) with 14, 16, 18, 20 y 22 teeth.

a) Calculate the gear ratio in the following situations:

Combination Gear Ratio

Biggest chain ring & cassette

Biggest chain ring & smallest cassette

Smallest chain ring & Biggest cassette

Smallest chain ring & Smallest cassette

b) The gear ratio of a bicycle is...

Always less than 1

Sometimes less and sometimes greater than 1

Always greater than 1

Equal 1

33. Calculate the gear ratio of the system and the speed of each gear if the driving gear (4) rotates at 800 rpm.(clockwise)

35. Look at the fruit squeezer in which the axle of the engine rotates a 10 teeth gear at 1800 rpm.

a) If the cogwheel “B” has 50 teeth, what speed will it rotate? b) The cogwheel “C” has 15 teeth and it’s joined to “B”, what speed will cogwheel “D” rotate if it has 45 teeth?

3ºE.S.O. BILINGUAL TECHNOLOGY I.E.S. PABLO NERUDA CURSO 2013-2014

UNIT 5.- MECHANISMS

Page 10

36. Look at these pictures.

Conventional screws have right-handed threads. To tighten a screw, turn the head or bolt clockwise, moving its top to the right. To loosen, turn counterclockwise, moving the top to the left. Righty Tighty Lefty Loosey is a helpful expression too!

a) Which direction will the gear move?

Anticlockwise

Clockwise

b) What system is it?

A reducing system.

A multiplying system.

A constant system. c) Is the worm gear reversible?

Yes

Not

It depends on the motion. d) Will the gear ratio greater or less than 1?

Greater.

Less.

Equal. e) Calculate the gear ratio if the gear has 24 teeth.

37. Answer the following questions:

A mechanism ,where the gear ratio is less than 1, will be ....

A reducing system.

A multiplying system.

A constant system. A mechanism, where the gear ratio is equal 1, will be...

A reducing system.

A multiplying system.

A constant system. A mechanism, where the gear ratio is greater than 1, will be...

A reducing system.

A multiplying system.

A constant system. What type of gears would you use to transmit the motion between right angled axles?

➢ Cylindrical ➢ Conical

Indicate the type of motion of the following mechanisms using a “T” for transmitting motion mechanisms or a “F” for transforming motion mechanisms.

Pulley Cam

Rack and pinion Block & tackle

Nut & Bolt Crankshaft

Worm gear Lever

Crank handle Eccentric cam

Crank link slider Gears with chain

Gear Train. Friction drives

Cogwheels Pulleys with belt

3ºE.S.O. BILINGUAL TECHNOLOGY

I.E.S. PABLO NERUDA CURSO 2013-2014

UNIT 5.- MECHANISMS

Page 11

38.Identify the following mechanisms shown in the pictures below and indicate whether they are (1) linear transmitting motion mechanisms (2) rotatory transmitting motion mechanisms (3) linear/rotatory transforming motion mechanism (4) linear/rotatory into alternating transforming motion mechanisms.

Nut & Bolt (3) 1 2 3 4 5

6 7 8 9 10

Example:

11 12 13 14 15

16 17 18 19 20