Simple & Compound Machines Division B: Simple Machines Division C: Compound Machines

Simple & Compound
Machines
Division B: Simple Machines
Division C: Compound Machines
Kris Tesh
• Compound Machines = Simple Machines, with:
•
•
•
•
Screws
Multiple simple machines working together
Friction Problems
Potential / Kinetic Energy problems
• Scoring:
• 50 points for Exam
• 40 points for two ratios
• 10 points for time
• 100 points total
[Beware of Significant Figures]
[0.2 pts per 1 % wrong]
[0.04 pts per second]
• Success:
•
•
•
•
Learn – Measurement, understanding of machines
Plan – Strategy for your team (What to study, how to practice)
Know the rules – Spirit and letter of rules
Logistics – Schedule, Food, Communication, Emergencies
Machines
• Machines make work easier: Multiply force or distance, or change the
direction of force. Mechanical Advantage (MA) is the factor by which force is
increased. Ideal Mechanical Advantage (IMA) is a “perfect world” result.
Actual Mechanical Advantage (AMA) accounts for losses.
• Work = Force x Distance – Work in = Work out
• MA = Force out / Force In
• MA = Distance In / Distance Out
• Force is measured in Newtons (N) (1kg on Earth pulls at 9.81 N)
• Distance is measured in Meters (m), Work in N*m (Joules)
• Work out / Work in = Efficiency
• Six Simple Machines:
•
•
•
•
•
•
Lever
Wheel and Axle
Pulley
Inclined Plane
Wedge
Screw
Machines
MA < 1 : Input force < Output force
Effort Force
Resistance Force
Effort
[
Distance
] Resistance
Distance
TORQUE is force that causes turning, Force x Distance from the turning
point.
Solve levers: Torque = 0
(Effort) x (Effort’s distance from Fulcrum) - (Resistance) x (Resistance’s distance) = 0
Or:
Effort x Distance = Resistance x Distance
1 Equation, 1 unknown - Can solve!
Class 1 Lever
MA can be any value
Resistance
Effort Force
Force
Solve levers: Torque = 0
(Effort) x (Effort’s distance from Fulcrum) - (Resistance) x (Resistance’s distance) = 0
Or:
Effort x Distance = Resistance x Distance
1 Equation, 1 unknown - Can solve!
Class 1 Lever
MA can be any value
Resistance
Effort Force
Force
http://www.citytechnology.org/stuff-thatworks/levers-have-a-lot-of-class
Class 2 Lever:
MA>1 (Large Force)
Effort
Resistance
http://www.citytechnology.org/stuff-thatworks/levers-have-a-lot-of-class
Class 3 Lever
MA<1 (Large Distance)
Resistance
Effort
http://www.citytechnology.org/stuff-thatworks/levers-have-a-lot-of-class
Gear
Gears, Belt Pulley, Wheel and Axle
Large-diameter and small-diameter turning
together
Either can provide Effort
IMA = Diameter of Drive / Diameter of Load
Belt Pulley
A free-spinning wheel (toy car) is not a machine!
Wedge
INCLINED PLANE
• Perpendicular force
SCREW
Rotary motion to Linear
Pitch P
Threaded fasteners
Large MA
Large friction losses
IMA = 2πL / P
PULLEY
• Create mechanical advantage
• Change force direction
1
4
What is the IMA?
• Count the strings that
move: 4
• IMA = 4
10 N
10 N
2
P1
20 N
3
20 N
P2
40 N
Resistance
Using Levers
A
B
Example:
B hangs 25cm from the Fulcrum
A hangs 10cm from the Fulcrum
A x 10 = B x 25
A = B x 25/10
A/B = 25/10
B
IMA = (25 / 10) = 2.5
A / B = 2.5
Using Levers
A
Class 1 Lever
Example:
B hangs 15cm from Fulcrum 2 (F2)
The end of the Class 2 lever is 30cm from F2
Want A/L2 and L1/B
L1 x 30cm = B x 15cm
L1 = B x 15/30
L1 / B = 15/30
A/B = A/L2 x L1/B = (10/15) x (15/30)
A/B = (10/15) x (15/30) = 1/3 = 0.33
A x 15cm = L2 x 10
A = L2 x 10/15
A/L2 = 10/15
B
Class 2 Lever:
Resistance
Fulcrum
Effort
Effort
Resistance
Fulcrum
Fulcrum
Effort
Resistance
“Identify this Lever.”
“There is a pulley system. You pull with 10N force on a rope for 3 meters, and the
load lifts 0.5m. What is the IMA?”
IMA = Distance in / Distance out. 3m / 0.5m = 6
“Which simple machine is a Windlass?”
“Identify these types of gears” (http://en.wikipedia.org/wiki/Gear )
“How does torque matter with levers?”
“A 10kg block is pushed 6m horizontally on a board, with force 42N. Calculate the
Coefficient of Friction.”
(F=μN. 42N = μ*10kg * 9.81N/kg – So 42N / 98.1N = μ)
• Compound Machines = Simple Machines, with:
•
•
•
•
Screws
Multiple simple machines working together
Friction Problems
Potential / Kinetic Energy problems
• Scoring:
• 50 points for Exam
• 40 points for two ratios
• 10 points for time
• 100 points total
[Beware of Significant Figures]
[0.2 pts per 1 % wrong]
[0.04 pts per second]
• Success:
•
•
•
•
Learn – Measurement, understanding of machines
Plan – Strategy for your team (What to study, how to practice)
Know the rules – Spirit and letter of rules
Logistics – Schedule, Food, Communication, Emergencies
• Machines
• Types of Simple Machines
• Torque and Force
• Lever Classes
• Simple Machines Math
• Identifying Simple Machines
• Applying Simple Machine Principles
Resources
• http://www.sciencenc.com/events.php
• http://soinc.org/simple_machines_b
• https://www.khanacademy.org/science/physics/work-andenergy/mechanical-advantage/v/introduction-to-mechanical-advantage
• http://www.wikipedia.org/
• Email me: [email protected]
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