Typ

General Concepts

10.1.1 Define mechanical advantage, velocity ratio and efficiency.

Mechanical advantage This is the factor that the machine multiplies the force put into itVelocity ratio A measurement of force amplificationEfficiency Mechanical efficiency is the effectiveness of a simple machine
Society of Robots website.

10.1.2 Calculate mechanical advantage (MA), velocity ratio (VR) and efficiency for simple mechanical systems.

MA = load/effort VR = distance moved by effort/distance moved by load Efficiency = MA/VR ----

Levers


10.1.3 Describe first-, second- and third-class levers.

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Identify load (L), effort (E) and fulcrum (F) in first-class levers (E–F–L, for example, see-saw, crowbar, scissors), second-class levers (E–L–F, for example, wheelbarrow, bottle opener, nutcracker) and third-class levers (L–E–F, for example, tweezers, broom, fishing rod).

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1st
2nd
3rd

10.1.4 Discuss the relevant efficiencies of the three classes of lever.

Class 1 & 2 levers are common as they provide a good mechanical advantage, on the other hand class 3 levers provide a MA near or below one.

10.1.5 Explain that, when a lever is in equilibrium, the net moment is zero.

When there is more than one force acting on a lever there will be more than one moment and a net moment can be calculated. If the the lever is not in motion i.e. in equilibrium then the net moment will be zero.
In a see-saw the moments (turning affect) at the fulcrum will be clockwise as well as anti-clockwise, therefore when a see-saw is balanced then it is said to be in equilibrium and the moments will be zero.
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10.1.6 Calculate mechanical advantage and effort for first-, second- and third-class levers.



Gears

10.1.7 Describe gear systems.

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10.1.8 Calculate velocity ratio for gear systems.


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10.1.9 Describe the function of different types of gears in a range of objects.

Use rack-and-pinion, bevel and worm gears.
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Rack and pinion
Bevel gears
Worm Gears

10.1.10 Explain a design context in which a compound rather than a simple gear train would be appropriate.

Consider the gearing system on a metal lathe designed to be changed to cut a specific type of thread. Consider ratios, mechanical advantage and changes.

10.1.11 Discuss the function of different types of gears in a range of objects.

Use rack-and-pinion, bevel and worm gears. ----

Belts


10.1.12 Describe a belt or chain drive system.

Consider profile, load, changes in load, and speed.

10.1.13 Calculate velocity ratio for belt or chain drive systems.

For chain drives...
  • Calculate VR as you would for gears ... just ignore the chain.
For belt drives ...
  • Velocity ratio = Diameter of driven pulley/Diameter of driver pulley
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10.1.14 Compare belt or chain drives and gear systems.

Consider profile, load, changes in load, and speed.

Belt or chain drives
Gear systems
Profile
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Load
The belt and chain tension strength is its limiter
Can provide or accept greater loads that belts or chains
Changes in load
Has a large range within which it can work. Change in load can occur quicker.

Speed
Greater range in speeds than gears, possibly faster as well.


10.1.15 Design a system to provide belt torsion to a belt-and-pulley system.

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Inclined plane


10.1.18 Describe an inclined plane.

Consider inclined planes, screw threads and wedges.
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Inclined plane
screw thread
Wedge

10.1.19 Explain the advantage of an inclined plane.

It allows you to raise a heavy load easily, it is believed that the ancients Egyptians used this simple machine in building the pyramids.
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