Presentation on theme: "Simple Machines. A machine is a device that makes doing work easier. Machines increase the force applied to an object. Ways to make work easier: Increase."— Presentation transcript:
A machine is a device that makes doing work easier. Machines increase the force applied to an object. Ways to make work easier: Increase force Increase distance Changing direction
Work Done By Machines Effort Force- force applied to a machine (F E ) Resistance Force-force applied by the machine to overcome resistance. (F R ) in Newtons N Input Work-work done by you on a machine (W in ) Output Work-Work done by machine (W out ) Work output is always smaller than work input due to friction.
Ideal machines If no friction was involved then W out = W in
Mechanical Advantage Number of times a machine multiplies the effort force. Calculated by: MA= Effort force / Resistance force
Efficiency Measure of how much of the work put into a machine is changed into useful output work by the machine.
Calculating Efficiency Efficiency = Work Output / Work Input x 100%
Simple machines 6 types
Levers A bar that is free to pivot, or turn about a fixed point. Effort Arm-distance from the fulcrum to where the effort force is applied. Three types of levers.
First Class lever Fulcrum located between the effort and resistance force. Used to multiply force. Changes direction of the force.
Second Class Lever Resistance force is located between the effort force and the fulcrum. Always multiply the force.
Third Class lever Effort force is located between the resistance force and the fulcrum. Always increase distance over which the resistance force is applied.
Mechanical Advantage of a Lever IMA-Ideal Mechanical Advantage IMA= Length of the effort arm =L e Length of resistance arm L r
1. What is the length of the resistance arm? 2. What is the length of the effort arm? 3. What is MA of the see saw above? 4. What is the resistance force in the diagram? 5. How much effort force would be needed to overcome the resistance force?
Answers m m 3. 1 MA = 3.5 m / 3.5 m N N MA = resistance force/effort force so 1 = 350 N / x 1x = 350 N 1 1 x = 350 N
Pulleys A grooved wheel with a rope, chain, or cable running along the groove. A first class lever. Can multiply the resistance force and change direction of the force.
Fixed Pulleys Attached to something that does not move. Only changes direction of the force. Effort force not multiplied, IMA is 1.
Moveable Pulleys One end of the rope is fixed and wheel is free to move. Multiplies force.
Mechanical Advantage of a Pulley System 1. MA = ______________2. MA = ______________3. MA = ______________
Answers to MA of Pulley Systems
Wheel and Axle A machine consisting of two wheels of different sizes that rotate together. IMA = Radius of the Wheel = R e Radius of the axle R a Mechanical advantage of a wheel and axle may be increased by making the radius of the wheel larger.
Inclined Plane A sloping surface that reduces the amount of force required to do work. IMA= effort distance___ = length of slope = I Resistance distance Height of slope h
Inclined Plane 1. What is the height of the inclined plane? 2.What is the length of the inclined plane? 3. What is the mechanical advantage of the inclined plane? 4. How much effort force would be needed to push the dump truck up the mountain?
Answers to MA of Inclined Planes m 2. 3,000 m MA = 3000 m / 100 m N=MA = resistance force/effort force so 30 = N / x 30x = N x = 500 N
Screw Inclined plane wrapped in a spiral around a cylindrical post.
Wedge An inclined plane with one or two sloping sides. Changes direction of the effort force.
Compound Machines Two or more simple machines used together.
Compound Machines Two or more machines linked so that the resistance force of one machine becomes the effort force of the second. The mechanical advantage of a compound machine is the product of the simple machines it is made up of.
Answers to Work Problems 2 1) A. 250,000 J3) A. 50 m B W B. 245 N C. 250,000 J C. 245 N 2) A. 0 J D. 3.2 s (d=1/2 gt 2 ) B. 22,968.8 J E s (V=gt) C. 64,312 J F. 12,250 J D J E m 4) 5500 W F. 525 N (∑F=1/2 mv 2 /d) 5) A N (set up as ratio) * B. 17,500N * C. 60% *