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 andInput force is applied to theother 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 leverconnected to a shaft. A wheel and axle is made of a lever orA pulley (wheel) connected toA shaft (the axle)• When the wheel is turned, theAxle 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 destroyed.

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• 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 energyand 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