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Year 11 GCSE Technology > Mechanisms > Flashcards

Mechanisms Flashcards

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1
Q

What are the types of motion? Describe and draw them.

A

The types of motion are:

  1. Rotary motion is turning round in a circle, such as a wheel turning. (It can be visualised/drawn as a full circle with one arrowhead)
  2. Linear motion is moving in a straight line, such as on a paper trimmer. (It can be visualised/drawn as a single straight line with a arrowhead)
  3. Oscillating motion is swinging from side to side, like a pendulum in a clock. (It can be visualised/drawn as a curved line (it cannot be a full 360 degree line - anything less) with an arrowhead on both ends of the curved line)
  4. Reciprocating motion is moving backwards and forwards in a straight line, as in the cutting motion of a saw. (It can be visualised/drawn as a single straight line with an arrowhead on both ends)
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2
Q

What rhyme can be used to identify the class of a lever? How can you use the rhyme properly?

A

The rhyme used to help identify the class of a lever is:

F L E
1 2 3

Fulcrum, load and effort.

To use the rhyme you find which letter is in the middle of the lever you wish to identify (as in where would the fulcrum, load and effort be in relation to each other on the lever).

If F is in the middle, the lever is a class one lever.

If L is in the middle, the lever is a class two lever.

If E is in the middle, the lever is a class three lever.

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3
Q

What classes of lever are the most common?

A

Class one or two levers are the most common because they provide a mechanical advantage (this means that with a small effort you are able to move a large load).

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4
Q

What is a lever? What are they used for? Why are there different classes of lever?

A

A lever is a rigid rod or beam which pivots about a fixed pivot point called the fulcrum.

Levers are used to change the direction of motion of a force, and to magnify or reduce forces.

There are three different classes of lever. In each class of lever the fulcrum, effort and load are arranged in a different way.

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5
Q

Give examples of a class one lever.

A
  1. Claw Hammer.
  2. See-saw.
  3. Crowbar.
  4. Bell Crank.
  5. Pliers.
  6. Scissors.
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6
Q

Give examples of a class two lever.

A
  1. Wheelbarrow.
  2. Sack Trolley.
  3. Micro Switch.
  4. Can Crusher.
  5. Nutcrackers.
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7
Q

Give examples of a class three lever.

A
  1. Shovel.
  2. Fishing Rod.
  3. Tweezers.
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8
Q

Draw a class one lever.

A
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9
Q

Draw a class two lever.

A
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10
Q

Draw a class three lever.

A
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11
Q

How does moving the fulcrum further/closer from the effort point affect the lever’s mechanical advantage? (Lengthening the end of the lever)

A

Moving the effort further away from the fulcrum makes the overall moment created bigger. (Moments = the perpendicular distance from the pivot multiplied by the force applied)

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12
Q

What material should a lever be made of?

A

Steel for example is a good lever material for it is a durable material.

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13
Q

What are gears?

A

Gears are toothed wheels fixed to rotating shafts. The teeth of each gear mesh (touch) together to transmit rotary motion and torque. Gears are used to increase or decrease the speed or power of rotary motion.

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14
Q

What is a simple gear train?

A

A simple gear train uses two gears on separate shafts, which may be of different sizes. If one of these gears is attached to a motor or crank then it is called driver gear. The gear that is turned by the driver gear is called the driven gear.

When two meshed gears are on separate shafts, we call this a simple gear train.

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15
Q

Draw the symbol for a meshed gear.

A
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16
Q

How does the rotation work between gears in a simple gear train?

A

If the driver gear rotates clockwise, the driven gear rotates anticlockwise.

If the driver gear rotates anticlockwise, the driven gear will rotate clockwise.

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17
Q

What is a Compound Gear Train System?

A

A Compound Gear Train System is whenever multiple gears occupy the same shafts. Compound Gear Trains are made up of Simple Gear Trains joined together by gears which occupy the same shaft.

Compound Gear Trains are used in machine tools, gear boxes and any mechanism where a large change in speed is required or where a range of speeds is required in a small footprint.

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18
Q

If you need two gears to rotate the same way what do you do?

A

You place an idler gear in between the two gears. Idler gears have no affect on speed and can be ignored in calculations

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19
Q

How do you calculate the gear ratio of two gears in a simple gear train?

A

Gear Ratio of a simple gear train:

The Number of Teeth on a Driven Gear / Number of teeth on a Driver Gear

OR

Driven / Driver.

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20
Q

How can you calculate the transmission/output speed of a gear train? What are the units?

A

Output Speed = Input Speed / Gear Ratio

Units = RPM

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21
Q

How do you calculate the Total Gear Ratio?

A

You find the gear ratio of each gear and its driver and then multiply all the gear ratios together to combine them.

For example, if you had a simple gear train which goes as the following - A, B and C. You would find the gear ratio of A and B, then the gear ratio of B and C (since B is the driver of C). Then multiply both gear ratios together to get the Total Gear Ratio.

Gear Ratio Total = Gear Ratio 1 X Gear Ratio 2

GRT = GR 1 X GR 2

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22
Q

What is a Bevel Gear? What are its advantages and disadvantages?

A

A Bevel Gear rotates rotary motion to 90 degrees.

Advantages:

  1. This gear makes it possible to change the operating angle.
  2. Differing the number of teeth on the gears allows for a change in gear ratio - and therefore a change in speed.

Disadvantages:

  1. One wheel of such gear is designed to work with its complementary wheel and no other.
  2. The Bevel Gear must be precisely mounted.
  3. The shaft’s bearing must be capable of supporting significant forces.
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23
Q

What is Worm and Worm wheel?

A

A Worm Wheel has one tooth which is wrapped along the diameter of the worm. It will transfer rotary motion through 90 degrees. The worm allows for a large reduction in RPM from a motor but a large increase in torque (tension).

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24
Q

What is a Rack and Pinion? Give an example of how it can be used in machines.

A

A Rack and Pinion translates rotary to linear motion OR oscillating to reciprocating motion.

A good use of a Rack and Pinion is found on the pillar drill quill, a car steering box or a lock gate.

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25
Q

What are Belts and Pulleys? What are their advantages over gears?

A

Belts and Pulleys provide another method of transmitting force and rotary motion from one shaft to another. Like gears, Belts and Pulleys can be used to change the speed of a machine. The advantages of Belts and Pulleys over gears are:

  1. They have the ability to slip.
  2. They require less maintenance.
  3. They do not need lubrication.
  4. They allow the driver and driven pulley to rotate in the same direction.
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26
Q

How can a driven and driver pulley be made to rotate in opposite directions? Draw how?

A

The driven and driver pulleys can be made to rotate in opposite directions by crossing over the belts.

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27
Q

How do you calculate the Velocity Ratio of a simple pulley?

A

Velocity Ratio of a simple pulley = Diameter of Driven Pulley / Diameter of Driver Pulley

28
Q

How do you calculate the Output Speed of Belt and Pulley System?

A

Output Speed = Input Speed / Velocity Ratio (of the belt and pulley system)

29
Q

What are the four types of common belt?

A

The four common types of belt are:

  1. Flat belt.
  2. Toothed belt.
  3. Round belt.
  4. Vee belt.
30
Q

What are V- belts? How are they used?

A

Vee belts are the most commonly used type of pulley belt. They fit tightly into the groove on the pulley wheel so that slip is reduced to a minimum. E.g. Pillar drilling machines. The belt can slip if too large of a force is applied.

The pillar drill uses a v- belt and employs two stepped cone pulleys. This allows the speed of the drill to be adjusted. The belt allows just enough slip to prevent an accident when using the pillar drill.

31
Q

How can you keep belts tensioned?

A

You can use a Jockey Pulley.

32
Q

What is a Jockey Pulley?

A

A Jockey Pulley can be added to push against the belt to keep it tensioned. The pulley pushes against the belt to take up slack and to keep it at a constant tension.

33
Q

What is a Toothed Belt?

A

Toothed belts are positive transfer belts (without slippage) and can track relative movement. These belts have teeth that fit into a matching toothed pulley. When correctly tensioned, they have no slippage, run at a constant speed, and are often used to transfer direct motion for indexing or timing purposes. They are often used instead of chains or gears, so there is less noise and a lubrication bath is not necessary.

34
Q

Give an example of where a flat belt is used.

A

In conveyor belts - at shopping tills.

35
Q

Give examples of where a toothed belt is used.

A

Toothed belts are used in Engine Timing Belts and in CNC Timing Pulleys.

36
Q

Give an example of where a V-belt would be used.

A

V- belts are used in Pillar Drilling Machines.

37
Q

What is a Chain and Sprocket? What are the disadvantages and advantages?

A

Chains and sprockets act in a similar way to a pulley system but are used when a positive drive is required where there can be no slipping. Typical applications include bicycle transmissions, engine timing chains and machine tools. A chain can span large distances.

Chains are made with links which pivot on hardened steel pivots.

Disadvantages of chains are that they require lubrication, are noisy in operation, stretch and require maintenance and can quickly wear a sprocket unless tensioned.

38
Q

How can you calculate the chain ratio for a sprocket and chain?

A

The calculation is the same for the simple gear calculation. Look for the number of teeth on the sprockets and ignore the chain.

The number of driven teeth on the sprocket/ The number of driver’s teeth on the sprocket.

Driven/Driver.

39
Q

What do cams and followers do?

What cams are mostly used for?

What are cams usually made of?

A

Cams and Followers convert rotary motion to reciprocating.

They are used in children’s toys and in the camshaft in an engine used to open and close the valves.

Cams can be made from any material, though beech would be used for children’s toys and mild steel for a more heavy duty use case.

40
Q

What is the Cycle in a cam?

What is the Rise in cam?

What is the Fall in cam?

What is the Dwell in cam?

What is the Stroke in cam?

What is the Crown in cam?

What is the Heel in cam?

A

Cycle: one complete rotation of the cam.

Rise: the section of cam causing lift.

Fall: the section of cam causing drop.

Dwell: the point on the profile of the cam where the follower does move.

Stroke: the distance between the highest and lowest points.

Crown: the highest point on the cam.

Heel: the lowest point on the cam.

41
Q

Where are pear shaped cams used?

What kind of motion does it provide?

A

Pear shaped cams are used on the shafts of cars.

The follower remains motionless (it dwells) for about half of the cycle of the cam and during the second half it rises and falls steadily.

42
Q

Where are eccentric cams used?

What kind of motion does it provide?

A

These cams are used in steam engines.

Eccentric cams produce a smooth motion.

43
Q

What kind of motion does a heart shaped cam provide?

A

Heart shaped cams allow the follower to rise and fall with “uniform” velocity. There will be a little bump as the follower travels over the lobes of the cam.

44
Q

What kind of motion does a snail cam provide?

A

Snail cams have a large dwell period followed by a steady rise and sharp fall of the follower. They are only able to rotate in one direction or the follower would get stuck.

45
Q

What are the properties of a roller follower?

A

A roller follower is used where there is little friction. It cannot be used on a snail cam and it will not follow the exact detail of a heart shaped cam.

46
Q

What are the properties of a flat follower?

A

A flat follower is a follower used for eccentric cams, its large flat base is easy to shape and can easily follow the shape. It will not be able to follow any detail in the cam.

47
Q

What are the properties of a knife follower?

A

A knife follower is shaped so that it will provide accurate replication of motion. It can fit into the lobes of a heart shaped cam and the cutout of a snail cam. This follower will rapidly wear away.

48
Q

What is Load?

A

Load is a mechanical stress. It can be static, trying to lift a large rock with a lever or dynamic, a car engine working to power a car up a hill. Think of a weight to be lifted or driven pulley or gear.

49
Q

What is Effort?

A

Effort is the measurement of the input power required to overcome a load.

50
Q

What is the Fulcrum?

A

The fulcrum is another name for a pivot. It is the point of rest about which a rigid beam becomes a moving body or lever.

51
Q

What is mechanical advantage?

A

Mechanical advantage is the measurement of a force amplification when using a mechanism. It takes the input force and trades it against the movement required. For instance if a pulley system has a MA of 2 the load will be half as light but the user will have to pull double the rope.

52
Q

What is velocity ratio?

A

Velocity ratio is the ratio of the distance through which the force applied to a machine moves and the distance through which the load moves. Think of gear ratio if the driven is three times as large the driver will have to move three times as far to make driven turn once.

53
Q

What is Efficiency?

A

A measurement of the effectiveness of a mechanism in transforming the power input to the power output. No mechanism is 100% efficient due to frictional, sound and heat loss.

54
Q

How do you calculate mechanical advantage?

A

Mechanical advantage = Load/Effort

55
Q

What is a pulley lifting system?

Draw a single pulley lifting system.

Draw a double pulley lifting system.

Draw a triple pulley lifting system.

A

A pulley is a form of class 1 lever with the centre of the pulley acting as the fulcrum. When a single pulley is used as a lifting device its only function is to change the direction of the tension force in the rope. This is useful as it is easier to lift something by pulling downwards rather than upwards. In order to raise the load the effort force has to be equal or just greater than the load.

There is no mechanical advantage when a single pulley is used.

56
Q

What ways can you tension a pulley?

A

You can use a jockey pulley or a tensioning pulley. You can tension the belts on the linisher by increasing the distance between pulleys.

Engine mounts on a nitro RC car allows for tensioning.

57
Q

If a question asks you “How far a rack will move for a set rotation of a pinion” what will you do?

How do you work out the movement of one revolution of the pinion using the number of rack teeth and pinion teeth?

A

You need to identify the pitch, the distance between each tooth on the rack and the teeth on the pinion.

To work out the movement of one revolution of the pinion =

(number of pinion teeth/ number of rack teeth) X 1m

58
Q

What is a bell crank used for?

A

Bell cranks are useful for changing the direction of motion or transmitting it usually 90 degrees.

59
Q

What is a parallel linkage?

A

Parallel linkages are used to make two or more parts of a mechanism move together and stay parallel to each other as the linkage moves.

60
Q

What are screw threads and what are the used for?

A

They make use of the inclined plane principle. If you wrap an inclined plane around a cylinder you get the same helix form as on a screw thread.

They can be used to provide powerful movements (e.g. car jacks)

To position things accurately (e.g. binoculars)

To hold things in place (e.g. bolts and screws)

61
Q

What is a crank and slider?

A

A mechanism consisting of a crank and a slider connected to the rotating crank by a rod. It converts rotary motion into reciprocating motion or vice versa.

62
Q

What is a ratchet and prawl?

A

A ratchet and pawl is a safety device to stop a winch from unwinding or a pulley from slipping. The ratchet can only turn in one direction.

63
Q

How do you calculate velocity ratio?

A

VR = Distance moved by Effort/Distance moved by Load

64
Q

How do you calculate mechanical advantage

A

Mechanical Advantage = Load/Effort

65
Q

How do you calculate Efficiency (%)?

A

(Mechanical Advantage/Velocity Ratio) X 100

66
Q

How can achieve a range of velocity ratios and diameters in a pulley?

A

Use a stepped cone vee pulley belt system.

Year 11 GCSE Technology (3 decks)

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