real work: the great pyramid built 2600 b.c. - requiring massive resources. estimated to have...
Post on 16-Jan-2016
214 Views
Preview:
TRANSCRIPT
Real Work:
The Great Pyramid
Built 2600 B.C. - requiring massive resources.
Estimated to have 2,300,000 stone blocks weighing from 2 – 30 tons and some weighing 70 tons.
The Great Pyramid
To finish in less than thirty years, the Egyptians would have had to cut, move, and lift about 200 blocks per day!
The mortar used is of an unknown origin. It has been chemically analyzed, but cannot be reproduced.
Great Pyramid
Known Machines used by the Egyptians:
Incline ramps { decrease effort },
wood logs { wheels }, and
large crowbars {lifting and moving}.
Welcome to a world full of machines!
There are machines all around us!
A machine is a device with moving parts that work together to accomplish a task.
Example: A bicycle transforms forces from your muscles into speed and motion.
Why do we need simple machines?
Work means that we are exerting force and moving something.
The 6 simple machines make our work easier. We expend less energy (force) by using simple machines.
Machines
The INPUT includes everything you do to make the machine work.
The output is what the machine does for you, such as going fast.
6 Simple Machines
All machines are made up of some of the
6 simple machines.
Levers Inclined Planes
Wedges Screws
Wheel and axle Pulley
The 6 Simple Machines
Lever Pulley
Wheel and Axle
WedgeScrew
Inclined Plane
Levers
There are three parts to a lever:
Load Force Fulcrum: support or
balance
Classes:
Levers help us
to do work more
effectively.
Levers
Mechanical Advantage
MA = Output Force (N) / Input Force (N) 1 Newton (N) = 0.228 pounds 1 Pound = 4.48 Newton’s (N)
Mechanical Advantage
Mechanical Advantages
Using levers
properly provides
Large
Mechanical
Advantages
Incline Plane (Ramp)
It is a slanted surface
It makes moving objects easier.
The longer the ramp – compared to its height the greater the MA.
Wedges
Wedges that split:
Your teeth! Every time you bite into something, you are using a wedge.
Wedges that cut:
A saw! A knife!
Wedges
Wedges that tighten:
A doorstop to keep the door open.
Wedges that hold things together:
A nail holds wood to a wall or other wood.
The longer and thinner the greater MA.
Wedges
A wedge is used to split, tighten, or secure a hold.
A wedge is usually a triangle shape with a sharp point.
If you apply force at one end, the wedge will go between something, in this case an ax splits a piece of wood.
Screw
The three parts to a screw: Head - Shaft - Tip The head is the part that you exert a force on. The shaft has ridges, called
threads that wind around the screw. As the screw is rotated it exerts a small force over a great distance.
The tip is sharp.
How to use a screw:
Fasten two things togetherWhen you turn it clockwise, the threads
cut a groove down and into the material, making a hole. The threads holds the screw tightly in place.
To remove the screw you turn it counterclockwise, thus the screw pushes up and out of the material.
The Wheel and Axle
Two or more wheels are connected by an axle.
The wheel turns with or around the axle.
This car wheel has a big axle that it rotates around when the car moves.
Why do we need wheels?
Wheels help us move heavy objects. They roll easily.Did you know a doorknob is really two
wheels connected by an axle? You can’t see the axle because it’s inside the door, but it’s there!
If there wasn’t an axle, the doorknob wouldn’t turn!
Another type of wheel: Gear!
A gear is a wheel with teeth. The teeth fit in between each other and
turn. When one gear turns, its teeth push
against the teeth of the other gear and they both turn.
There are gears on your bike, on a can opener and on an egg beater.
Gears
If one gear has 36 teeth and the other has 12 teeth, then the smaller one would have to turn three times for the larger (36 teeth) gear to rotate once.
3 X 12 = 36
Pulleys
Lifting a bucket full of water is a lot of work!
A pulley is a wheel with a rope running over it. The wheel has a groove, called a sheave, and it keeps the rope from slipping off the wheel.
Remember, since there is a wheel in a pulley there also has to be an axle!
Block & Tackle
The Block and Tackle
is another simple
machine that uses
ropes and pulleys to
multiply forces.
Block & Tackle
Mechanical
Advantage = 2
Output / Input = MA
10 (N) / 5 (N) = 2
Block & Tackle
Note the number
of ropes yielding
greater output
capacity, thus
a larger MA.
Problem
Suppose a
Woman raises
a 65 N object
1.6 m in 4 s.
The work done
and her power
can be
Calculated:
W = F x D
65 N x 1.6m = 104J
P= W / T
104J / 4 s = 26 W
top related