SIMPLE MACHINES, WORK, AND POWER!
Pyramid Mystery (do not write) The Great Pyramid of Giza of Egypt is one of the Great Seven Wonders of the world. It covers enough area to hold ten professional football fields and it is made of 2 million stone blocks, each weighs about the weight of two large cars. It was built using only simple machines and has endured weathering and time. Today it would take five years and a few hundred workers with machinery to build it.
The Great Pyramid
Images of Failure…#1
What is work? Work is a force acting through a distance. Holding a pile of wood for an hour is NOT work. But, carrying feathers from one side of the room to another is. Why?
What is work?
Calculate Work… Work = Force x Distance Work is measured in newton-meters or joules. If you lifted an object weighing 200 N through a distance of 5 m, how much work did you do?
#2
Power Power is the rate at which work is done Power is measured in watts. Power = work/time Power = force x distance time
What is Power?
Machines… Machine – an instrument that makes work easier. Work input – the work that goes into the machine. Work output – the amount of work done by the machine. Machines make work easier because they change the size or the direction of the force put into the machine.
#3
Machine Terminology Efficiency – the comparison of work output to work input. Work output can never be more than work input. Mechanical Advantage – the number of times a machine multiplies the effort force.
Machines and Efficiency
Simple Machines There are six simple machines
#4
#1 Inclined Plane – a flat slanted surface. Mechanical advantage increases as the slant decreases. Ex: a ramp.
Inclined Plane
#2 Wedge – an inclined plane that moves. Usually a piece of wood or metal that is thin/sharp at one end. Mechanical Advantage increased by sharpening it. Ex: door stop, ax, knife, zippers
Wedge
Failure #5
#3 Screw – an inclined plane wrapped around a central bar, or cylinder, to form a spiral. Mechanical advantage increased by number of threads. Ex: the screw
Screw
#4 Lever – a rigid bar that is free to pivot (move) on a fixed point. The fixed point is called the fulcrum. 1 st class – fulcrum is in the middle Ex. seesaw 2 nd class – fulcrum is away from you Ex. wheelbarrow 3 rd class – fulcrum is near you Ex. Fishing pole.
Types of levers
Lever
Failure #6
#5 Pulley – a rope, belt, or chain wrapped around a grooved wheel. Changes the direction of the force needed. Mechanical advantage - increased by adding pulleys. Ex: blinds
Pulley
#6 Wheel and axle –The wheel is larger and turns the smaller axle. Mechanical advantage depends on the radius (size) of the wheel and of the axle. Ex: bicycles, ferris wheels, gears, etc…
Wheel and Axle
Table talk: How would you classify a gear?
Compound Machines A compound machine is two or more simple machines in one. Ex: washing machine, blender, sewing machine, vacuum cleaner, etc… Remember: you can only get the same amount of work out of a machine that you put into it!
Build your own “compound” machine…
How to Keep Shop Windows Clean Rube Goldberg stands in front of an x-ray and sees an idea inside his head showing how to keep shop windows clean. Passing man (A) slips on banana peel (B) causing him to fall on rake (C). As handle of rake rises it throws horseshoe (D) onto rope (E) which sags, thereby tilting sprinkling can (F). Water (G) saturates mop (H). Pickle terrier (I) thinks it is raining, gets up to run into house and upsets sign (J) throwing it against non-tipping cigar ash receiver (K) which causes it to swing back and forth and swish the mop against window pane, wiping it clean. If man breaks his neck by fall move away before cop arrives.
Explain what is occurring at each letter…
More on Rube Goldberg…
Last one!