Transcript Chap-13 Simple Machines and its - Environmental-Chemistry

Classification of simple machines:
Simple machines are divided into two
families: 1)The Lever family and
2) The inclined plane family
The Lever family
Simple lever
Pulley
Wheel & Axle
The inclined plane family
Inclined plane
Wedge
Screw
The classes of Lever
• First class of Lever: It has
fulcrum located between the
input force and the output force.
• Second class lever: The fulcrum
Is at one end of the arm and
Input force is applied to the
other end, ex. Wheelbarrow.
• Third class of lever: The input
force is in between fulcrum and
output force.
Types of Pulleys and their MA
• Fixed pulley: The
pulley is fixed with
support. It has MA = 1
since used to change
direction of force.
• Movable single
Pulley: The pulley is
not fixed with support,
it can increase the
MA, the load is
shared by two
sections of rope
pulling upward.
Block and tackle
• Using movable pulleys
or more than one pulley
at a time can increase
the mechanical
advantage.
• Multiple pulleys
combined into a
single unit is called a
Block and tackle.
• All of the sections of
rope are pulling up
against the downward
force of the weight.
Wheel and Axle
• A wheel and axle is a lever
connected to a shaft. A wheel
and axle is made of a lever or
A pulley (wheel) connected to
A shaft (the axle)
• When the wheel is turned, the
Axle also turns.
• When a small input force is applied to a
steering wheel, the force is multiplied to
become a large output force which turns the
front wheel of the car. Other ex: screw driver
Gears:
• A wheel with teeth is known as Gear.
• Some machinery, such as small drills requires small
force at high speed and such as mill wheels, require
large force at low speed.
• Gears are used to change the speeds of rotating
shafts. By using gears of different sizes, the shaft can
be made to turn at different rate.
• Gear ratio: TO/Ti = Ni/NO Ti = turns of input gear
TO= turns of output gear, Ni = # of teeth on input gear
NO = number of teeth on output gear
The mechanical Advantage of
pulleys
Difference between wheel and axle
& Pulley
The inclined plane: MA = l/h
• An inclined plane
reduces the force
needed to lift an object
by applying the force
over longer distance.
• A type of sloping
surface used to raise
objects is called
inclined plane, for
example: a ramp
• Pushing an object up
an inclined plane
requires less input force
than lifting the same
object does.
• MA = length of slope
divided by height slope
A simple Machine: Screw
• A screw is an
inclined plane
wrapped in a spiral
around a cylinder.
For example,
A drill bit, Jar lids
and spiral staircases
are screws that we
use everyday.
• Screws:
A simple machine: Wedge
• A wedge turns a
downward force into
two forces directed
out to the sides.
• A wedge is a
modified inclined
plane with one or
two sloping sides.
• Chisels, knives, and
axe blades are
examples of wedge
• In a wedge, the
material remains at
one place while
wedge moves
through it.
Compound Machines &
Human Powered Flying Machine
• Compound Machine: Many devices that are
made of more than one simple machine.
• A compound machine combines two or more
simple machines. For example, a pair
scissors, a bicycle are compound machines.
• A human powered aircraft designed at
Massachusetts Institute of Technology, the
Daedalus has pedals like a bicycle. The plane
is human powered because the pilot’s legs
are the only source of power.
Section-3: Energy and Work
• Energy is ability to do work. Whenever
work is done, energy is transformed or is
transferred from one system to other system.
• Measurements of energy and work are
expressed in the same units - “Joules”
• The energy in an object can be calculated
whether the object is in motion or at rest.
• Energy exists in many different forms.
According to energy conservation law, one
form of energy can be transformed to other
forms of energy but energy can't be created or
Potential Energy: PE
• Potential energy: The energy that an object
has because of the position of an object, its
shape, or molecular structure of the object.
• The stored potential energy that results from
gravitational attraction between the objects is
called gravitational potential energy.
• PE = m.g.h
• Where, m=mass
h=height or position of an object
g=gravitational acceleration=9.8 m/s2
Kinetic Energy: KE
• Kinetic Energy: The energy in an object due
to object’s motion
• Kinetic energy depends on two factors, the
mass and the speed of an object.
• KE = ½ m v2
Where, m = mass of an object and
v = speed of an object
The unit of kinetic energy is kg.m2/s2
That is kilograms times meter squared per
second squared.
•Atoms and molecules have kinetic energy.
Other forms of energy
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Mechanical energy
Chemical energy
Solar energy
Nuclear energy
Electro magnetic energy
Light (radiant) energy
Thermal (heat) energy
Hydro energy
Tidal energy
Wind energy
Electrical energy
Other forms of energy
• Mechanical energy: The sum of the kinetic
energy and the potential energy in a system is
called mechanical energy.
• All objects have some stored potential energy
according to arrangement of atoms that make
up the objects in the system.
• Chemical reactions involve potential energy.
• Living things get energy from sun through
electromagnetic waves.
• Plants use photosynthesis to turn energy in
sunlight into chemical energy.
Other forms of energy……..
• Solar energy: The sun gets energy from
nuclear reaction; nuclear fusion, a kind of
reaction in which light atomic nuclei combine
to form a heavier nucleus.
• Nuclear power plants use Nuclear fission, to
release nuclear energy. In nuclear fission a
single large nucleus is split into two or more
smaller nuclei.
• In both nuclear fusion and fission, small
quantity of mass are converted into large
quantities of energy.
Other forms of energy………..
• Electrical energy: 1) The electrical energy is
derived from other sources of energy.
• 2) In a natural gas power plant in the gas is
chemical potential energy.
• 3) When gas burned, releasing energy in form
of heat is used to make high pressure steam.
• 4) The steam turns the turbine which
transforms heat energy into mechanical
energy.
• 5) Finally the turbine turns an electrical
generator producing electrical energy.
Light energy
and electromagnetic waves
• Light can carry energy across empty space.
• The object in direct sunlight is hotter because
light carries energy.
• Light energy travels from sun to Earth across
empty space in the form of electromagnetic
waves.
• Electro magnetic waves are made of electric
and magnetic fields, so light energy is an
example of energy stored in a field.
Efficiency of machines
• All of the work done by machine is not useful
work. Only a portion of the work done by any
machine is useful work.
• In real machine, the work output is always
less than the work input because other forces
like friction use up some of the input work.
Some input work is being converted to heat.
Therefore the work output is reduced by the
work that is converted to heat.
• The efficiency is a quantity, usually expressed
as a percentage, that measures the ratio of
useful work output to work input.
Efficiency of machines……..
• Efficiency =
(work output / work
input) x 100
• In reality, no machine is
100 % efficient
• Practically perpetual
motion (machine with
no loss of energy)
machine is impossible.
• Machines always need
energy input.
Math problem: efficiency of machine
• Alice and Jim calculate that they must do
1800 J of work to push a piano up a ramp.
However, because they must also overcome
friction, they actually must do 2400 J of work.
What is the efficiency of the ramp?
Given:
• Output work=1800 J
Input work = 2400 J
• Efficiency = (work output/work input)*100
= (1800 J/2400 J) * 100
= (0.75) * 100
= 75 % efficiency of the ramp.
Math problem: potential energy
• (Pg.446-prblem # 3) A diver has 3000 J of
gravitational potential energy after climbing up
onto a diving platform that is 6.0 m above the
water. What is the diver’s mass in kilogram?
• Rearrange the equation for mass
• PE = m ×g × h Therefore, m = PE / g ×h
• Given: PE= 3000 J, h= 6.0 m, g= 9.8m/s2
• M= 3000 J / 6.0 m × 9.8m/s2 = 49.7 kg
• Mass = nearly 50 kg.
Math problem: kinetic energy
• (Pg-448 problem # 2) A 35 kg child has 190 J
of kinetic energy after he sleds down a hill.
What is the child’s speed at the bottom of the
hill?
• Rearrange the KE equation to isolate speed
on the left. KE= ½ m.v2
m= 2KE/v2
• therefore v2= 2 KE/m,
v=√ 2 KE/m
• Given: m= 35 kg, KE= 190 J v= ?
• v= √2 ×190 J/35 kg = 30.8 m/s2
• Speed = 30.8 m/s2