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A set of slides created to teach Mechanical Advantage to learners at Bishops Diocesan College in Cape Town.

A set of slides created to teach Mechanical Advantage to learners at Bishops Diocesan College in Cape Town.

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### Transcript

K WARNE
• 2. Moments and levers
Definition
Principle of moments
Couples
Calculations
Classes
• 3. Moment of Force
The moment of a force about a point is the ……………….of the magnitude of the force and the perpendicular distance from the point to the line of the force.
• 4. Moment of Force
The moment of a force about a point is the PRODUCT of the magnitude of the force and the perpendicular distance from the point to the line of the force.
MOMENT = FORCE X DISTANCE
• 5. Equilibrium
For an object to be in equilibrium BOTH the sum of the …………….. acting on the object and the sum of the …………….of the forces must be ZERO.
Solve problems involving objects in equilibrium.
If a 60 Kg person stands 2 meters from one end of a 3 meter scaffolding plank what force is needed to support each end of the plank?
F2
x1
F3
F1
x2
FORCES (Linear) in equilibrium .: F1 + F2 +F 3 = ……
MOMENTS in equilibrium .: ……………. a fulcrum. (F1)
(F1….) + (F2…..) + (F3……) = 0
• 6. Equilibrium
Know that for an object to be in equilibrium BOTH the sum of the FORCES acting on the object and the sum of the MOMENTS of the forces must be ZERO.
Solve problems involving objects in equilibrium.
If a 60 Kg person stands 2 meters from one end of a 3 meter scaffolding plank what force is needed to support each end of the plank?
F2
x1
F3
F1
x2
FORCES (Linear) in equilibrium .: F1 + F2 +F 3 = 0
MOMENTS in equilibrium .: Choose a fulcrum. (F1)
(F1.0) + (F2.x1) + (F3.x2) = 0
• 7. Equilibrium
Know that for an object to be in equilibrium BOTH the sum of the FORCES acting on the object and the sum of the MOMENTS of the forces must be ZERO.
If a 60 Kg person stands on one end of a 3 meter scaffolding plank what force is needed to support him on the other end of the plank if the plank is balancing on a fulcrum 2m away from the 60kg person?
F2
60kg
F1
x1
x2
2m
FORCES (Linear) in equilibrium .: F1 + F2 +F 3 = 0
MOMENTS in equilibrium .: Choose a fulcrum. (F1)
(F1.0) + (F2.x1) + (F3.x2) = 0
• 8. Levers
• Describe the terms “load” and “effort” for a lever
• 9. Define “mechanical advantage” as the ratio of “load/effort” and calculate the mechanical advantage for simple levers
Ifin equilibrium: …… x …..= …… x …..
E
................
…………..
L
……
........
• 10. Levers
• Describe the terms “load” and “effort” for a lever
• 11. Define “mechanical advantage” as the ratio of “load/effort” and calculate the mechanical advantage for simple levers
If in equilibrium: E x e = L x l
E
Effort
L
e
l
Apply the concept of mechanical advantage to everyday situations.
?
N
……..
……..
Apply the concept of mechanical advantage to everyday situations.
N
N
Effort
• 14. Types of Levers
Class 1
Effort
Effort
• The three classes of lever are shown here.
• 15. By considering the mechanical advantage of each decide which give the best.
• 16. (Consider a 1m bar being used for each type.)
Class 2
Effort
Effort
Class 3
Effort
• 17. Types of Levers
Class 1
Type 1
MA = e/l= 0.75/0.25 = 3
Type 2
M.A. = e/l = 1/0.25 = 4
Type 3
M.A. = e/l = 0.25/0.75 = 0.3
The weight of the lever helps in type 1 but not T2!
Effort
Effort
o.25
o.75
Class 2
o.25
o.75
Effort
Effort
Class 3
o.25
o.75
Effort
• 18. Examples of Levers
• 19. Force Couple
A special case of moments is a ................
A couple consists of two ...............forces that are .......... in magnitude, opposite in ..................and do not act in a ...................... line.
It does not produce any translation, only ................
The resultant force of a couple is zero. BUT, the resultant of a couple is not zero; it is a pure moment.
• 20. Force Couple
A special case of moments is a couple.
A couple consists of two parallel forces that are equal in magnitude, opposite in direction and do not act in a straight line but are separated by a distance (d).
It does not produce any translation, only rotation.
The resultant force of a couple is zero. BUT, the resultant of a couple is not zero; it is a pure moment.