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