Mechanisms (Y10 - Spring 1)

Question 1

What is Linear Motion (+ Example)

Answer 1

Example: Motion of a Train

A moving motion in a straight line travelling in one direction.

Question 2

What is Reciprocating Motion (+ Example)

Answer 2

Example: Motion of a Jigsaw Blade

A repetitive back-and-forth or up-and-down linear action.

Question 3

What is Oscillating Motion (+ Example)

Answer 3

Example: Motion of a Swing

A repetitive back-and-forth motion along a curved path e.g a pendulum.

Question 4

What is Rotary Motion (+ Example)

Answer 4

Example: Motion of the Hands of a Clock

Objects moving in a circular motion, usually around a fixed point.

Question 5

What is a Mechanism

Answer 5

A mechanism is simply a device which takes an input motion are force, and outputs a different motion and force. The point of a mechanism is to make the job easier to do. The mechanisms most commonly used mechanical systems are levers, linkages, cams, gears, and pulleys.

Question 6

What is a Mechanical Advantage

Answer 6

How much easier a job is, is called the mechanical advantage. This can be calculated by using the following equation:

MA (Mechanical Advatage) = Load (Newtons) / Effort (Newtons)

Question 7

What are Levers

Answer 7

A lever is a simple mechanism thatbuses mechanical advantage to make a job easier. There are three classes of lever that are determined by the position if the load, the effort, and the fulcrum.

Question 8

What is a Class 1 Lever (+ Example)

Answer 8

Example: A Claw-Hammer

A First Class lever has the load and effort on opposite sides, with the fulcrum (pivot) inbetween them.

The mechanical advantage can be improved by moving the pivot closer to the load.

Question 9

What is a Class 2 Lever (+ Example)

Answer 9

Example: Wheelbarrow

A second class lever has the pivot point at the front, with the load in the middle, and the effort at the end.

The greater the distance between the load and the effort, the greater the mechanical advantage.

Question 10

What is a Class 3 Lever (+ Example)

Answer 10

Example: Stapler

A third class lever is a lever in which the fulcrum is at the front, with the effort sustained in the middle, and the load a the end.

A third class lever has no mechanical advantage and is used where a small effort is required to move the load. They are usually used t make ajob easier, such as picking up small objects with a pair of tweasers.

Question 11

Equilibrium Definition

Answer 11

When the effort and the load are equal, equilibrium can be created in a mechanism.
(This links to moments)

Question 12

What is a Linkage

Answer 12

Linkages are mechanisms that uses rigid parts to:

• Provide uniform movememt of different components
• Change the direction of a force/movement
• Transform it into a different motion
• Change the magnitude of a force

Question 13

What is a Parallel Motion Linkage (+ Example)

Answer 13

It is known as a push/pull linkage, as it keeps direction of the output the same as the input.

-There will be a fixed pivot and other pivots that allow the linkages to move.

Example: The Opening up of an old Toolbox

(More info on Goodnotes Flashcards)

Question 14

What is a Bell Crank Linkage (+ Example)

Answer 14

The input direction is converted through 90 degrees.

• It changes horizontal motion to vertical and vice versa
• Often found in steering and throttle mechanisms on vehicles

Example: Lever used in a Bike Brake

(More info on Goodnotes Flashcards)

Question 15

What is a Reverse Motion Linkage (+ Example)

Answer 15

This changes tne direction of the input motion

• If the input is pulled, the output will push
• The linkage uses a fixed central pivot

Example: A Clothes drying hanger (when it gets opened up, each side comes in Reverse Motion)

(More info on Goodnotes Flashcards)

Question 16

What is a Crank and Slider Linkage (+ Example)

Answer 16

Crank and sliders convert rotary motion into reciprocating motion into reciprocating motion and vice versa

• A linkage commonly found in engines to transfer the nergy from pistons
• The slider is guided along a set path

Example: When used in a car engine, the ignition of petrol by the spark plugs pushes the slider up, moving the connecting rod and turning the crank.

(More info on Goodnotes Flashcards)

Question 17

What is a Pulley System? (+Examples)

Answer 17

A pulley system can be used to make the liftling of loads easier. By using a series of pulleys, it is possible to decrease the amount lf effort required to lift a given load.

As you cam see in this example, to lify the load requires half the effort (measured in Newton), but the load only mobes half the distance travelled by the rope that is being used to pull.

This trade-off does allow much heavier loads to be lifted with relative ease.

Examples:

• Pulley systems are iften used on sailing boats when rigging the sails.
• Pulley system used to lift a bike for storage in a garage.

Question 18

The Mathematical formula to work out the Effort Required by a Pulley System

Answer 18

Effort = Load / Number of Pulleys

Question 19

What are Gears and Chains used for in a Bike, andhow it can afect the Velocity Ratio

Answer 19

Gears and chains are used to create mechanical advantage and make tasks easier. In the example of a bike, the gears are used to change the number of times the wheel rotates each time the crank (pedal) completes a full revolution. The difference in speed between the driven sprocket (the one attached to the wheel in the case of a bike) and the driver sprocket (the one attached to the crank / pedals on a bike) is known as gear ratio or velocity ratio.

Question 20

What is the Mathematical Equation for Velocity Ratio

Answer 20

Velocity Ratio = Number of Teeth on the Driven Sprocket / Number of teeth on the Driver Sprocket

Question 21

What is the Driven Sprocket and what is the Driver Sprocket?

Answer 21

The Driven Sprocket is the one that is moving as a result of the driver sprocket (e.g the sprocket at the back of a bike).

The Driver Sprocket is the one that needs to be moved by the person exerting the effort. The Driver Sprocket will, in turn, move the Driven Sprocket (e.g the sprocket at the front of a bike where the pedals are).

Question 22

If a Velocity Ratio was 2/1, or 2 : 1 on a bike, then how would it affect the Speed in which you travel at and the Effort you exert.

Answer 22

The difference you would see is that you would have to pedal two times for one rotation of the wheel when going uphill, for example. This means it will take longer to go up the hill, but you will use less effort.

Question 23

Why might a belt-driven pulley system be chosen over a chain-driven gear system?

Answer 23

A belt-driven pulley might be chosen over a chain-driven gear systems for many reasons. Some of these might be the fact that Gears without chains are able to change the speed and can create a mechanical advantage, whereas chain-driven gear system cannot do this as well. Also, chain gear systems can, at times be quite, fiddley, while the chains can sometimes be prone to breaking or falling off.

Question 24

Explain why gears are used within a mechanical system?

Answer 24

Gears are used in mechanical systems mainly to give the user a mechanical advantage, and to therefore, make their own lives a lot easier as a result. A good example of where gears are used to make things easier is in bikes. When you are approaching a hill, you can change the gear on your bike, meaning the Velocity Ratio will be altered in your favour, making riding up a hill easier, but you will be slower as a result.

Question 25

Give an example where gears are used and explain what they are used for? (Example of where Gears are used + Explanation of what they do

Answer 25

Example: Car Gear System

Explanation: Car gears, can allow a car to be driven with as little strain, or effort exerted on/by the engine as possible. Cars usually have around 6 gears, in which can be changed in relation to the vehicle’s speed and direction of travel.

Question 26

Explain what an idler gear is and why it might be used

Answer 26

An idler gear is essentially a smaller gear that can sit between two larger gears, in order to change back the direction of motion back to what the first gear’s direction was, allowing the second gear to travel in the same direction. If the idler gear was not there, the two gears that are next to each other would travel in opposite directions.

Question 27

Worm Gear Description

Answer 27

Worm gears can be used to transfer motion by 90°. A worm gear only has one ‘tooth’ that works like a screw thread.

Question 28

Bevel Gear Description

Answer 28

Bevel gears also change the direction of rotation by 90° but different sized gears can be used to change the speed of rotation.

Question 29

Rack and Pinion Gear Description

Answer 29

A rack and pinion gear changes a rotary motion into a linear motion. This is usually a fairly small linear movement that goes in one direction and then back again.