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Work

09.23 |


Work
Work is done when an object moves from one place to another
Work is measured with the formula
Work = Force x displacement
So
                                W  = F x d
                                     = N x m
                                     = Joule
Work is done when
—  There is force which acts on the object
—  An object moves
—  The motion of an object is in the direction of force
Example
—  Calculate the work done is pulling a wooden block with a force of 20 N through a displacement of 1.5 m
Solution
Work done = force x distance
                                                  = 20 N x 1.5 m
                                                  = 30 J
—  Calculate the work done to lift a load of 500 g onto the surface of the table, if height of table is 0.8 m
Solution
                                W = F x d
                                     = (m x g) x d
                                     = 0.5 kg x 10 N/kg x 0.8 m
                                     = 4 J
Power
—  Power is the rate of work done
—  Power is measured in joules per second    ( j s-1 ) which is also called as Watt (W)
—  Power is measured with the formula :
—  Power = Work /Time
           P = W / t
Example
—  A student of mass 50 kg climbing a distance which is 10 meters high. The time taken to climb the staircase is 20 second.(1 kg = 10 N)
  1. Find the power while climbing the staircase?
  2. To produce twice the power. Find the time taken by the student
Solution
  1. Power = (500 N x 10 m)/ 20 s = 250 W
  2. Time taken = (500 N x 10 m )/ (2 x 250 W )
                                                       ENERGY
The Definition of Energy
Energy is the ability to conduct work. The unit of energy in SI is joule (J). The other unit for energy is calorie (cal). The relation between joule and calories is as follows.
                1 calorie  = 4.2 joule or
                1 joule = 0.24 calorie
Forms of Energy
  1. Heat energy
  2. Electric energy
  3. Sound energy
  4. Light  energy
  5. Nuclear energy
The use of energy in daily life
  1. Solar energy       d. Geothermal Energy
  2. Wind energy      e. Tidal energy
  3. Water energy    f. Nuclear energy
ENERGY resource
ž  Non renewable
›      Oil (petroleum)
›      Natural gas
›      Coal
›      Uranium (nuclear)
ž  Renewable
›      Solar
›      Wind
›      Geothermal
›      Biomass
›      Hydro
›      Ocean
The form of energy exchange
Energy can be transformed into many forms, such as :
ž  Light to heat
ž  Electric to light
ž  Electric to heat
ž  Electric to sound
ž  Chemical to electric
The form of energy exchange
ž  Energy can be transformed into many forms, but the amount of energy is constant. There is no increasing or decreasing.
ž  Only the form of energy has changed, not its amount.
KINETIC Energy
ž  Kinetic energy is the energy in the form of movement, such as:
›      The running children
›      The rock fall
›      The running car
Variable that have
ž  Kinetic energy depend on the mass and velocity of the moving object
›      The larger the mass, the larger its kinetic energy
›      The thing move faster, its kinetic energy become larger
Formula of kinetic energy
ž  We can write formula kinetic energy
KE = ½ m v2
›      KE = kinetic energy (joule)
›      m= mass of moving object (kg)
›      V = velocity of moving object (m/s)
Unit of kinetic energy
ž  Unit of kinetic energy in SI system is:
›      Joule
›      Kg m2/s2
›      N.m
›      Watt. Second
ž  Another unit is:
›      Kalori      1 Kalori = 4.2 joule
POTENTIAL Energy
ž  Potential energy is the energy stored
ž  Its amount depend on
›      its the position  or condition of the object
–   If its position so higher, its potential energy is greater
›      Its mass
–   The higher its mass, its potential energy is greater

Formula of gravitational potential energy
ž  We can write formula gravitational potential energy
PE = m g h
›      PE = gravitational potential energy (joule)
›      m = mass of object (kg)
›      h = high (m)
Unit of potential energy
ž  Unit of potential energy in SI system is:
›      Joule
›      Kg m2/s2
›      N.m
›      Watt. Second
ž  Another unit is:
›      Kalori
Conservation of Energy
ž  The potential energy is changed from kinetic energy continuously.
ž  Potential and kinetic energy together in form mechanical energy.
ž  It is a sum of potential and kinetic energy in a system
ž  Formula of mechanical energy
Em = Ek + Ep
ž  Em = mechanical energy
ž  Ep  = Potential energy
ž  Ek  = kinetic energy
ž  Energy can be transformed in one form to another, but its total energy is constant. In other word, energy is conserved.
ž  That is called the law of energy conservation
ž  Em1 = Em2 = Em3= Constant







Theory of Atom
  • Atom
                Atom is the smallest part of element
  •  John Dalton Theory
1. Each elements consist a small particles which is called atom
2. Atoms of each element have a same of characteristic, size and mass     
3. Compound is a substance that consist of more than one atom.
4. Chemical reaction is not change the characteristic of atom, but only change the composition only.
Rutherford Theory
“Mass of  atom center in nucleus, which have a positive charge”
Niels Bohr Theory
Atom have a central nucleus made up of protons and neutrons.  And  electrons move around the nucleus.
THE INVENTOR  OF PARTICLE SUB  ATOMIC
  • J.J Thomson, 1897  -----> electron
  • Ernest Rutherford, 1911 ----> proton
  • James Chadwick, 1932 ----> neutron
                             Electron symbol     ( e )
Proton symbol        ( p )
Neutron symbol      ( n )
Catatan : Massa  adalah dalam satuan massa  atom (sma)
                  Massa elektron sangat kecil, sehingga massanya = 0 sma
WRITE THE SYMBOL  OF ATOM
 X = Name of Atom/Chemical Symbol
A = Atomic Number
Z = Mass Number
Atomic Number  shows the number  of  protons or electrons in its atom.
Mass number shows the total number of protons plus neutrons in the nucleus.
  • Molecule of Element
                A molecule that is composed of  similar atoms.
  • Molecule of Compound
   A  molecule is composed of different atoms.

 Molecule of Compound
Molecule
 1. Element  : - Monoatomic Element  ( He, S, Fe, Ca, dll)
                         -  Diatomic Element (O2, N2, H2, dll)
                         -  Poliatomic Element (O3, P4, dll)
 2. Compound  : - Diatomic Compound  (NaCl, HCl, KCl, HBr, dll)
                              - Poliatomic Compound (H2SO4, NaOH,C6H12O6)
Isotopes, isobar, dan Isoton
The atoms of an element are not all alike. Some have more neutrons than others. These different versions of the element are called  isotopes.
Lithium have two isotopes with mass number 6 and 7.
The symbol of Lithium :
                Li-6    or   Li-7
Isotopes
                Isotopes have different  mass numbers but the same atomic number.
Isobar          
              Isobar have different atomic number but  the same mass number.
Isoton
                Isoton have different both atomic number and mass number but the same amount of neutrons.
PRESSURE
Science word
  Pressure 
  Force
  Area
  Fluids
  Archimedes principle
  Flooding
  Flying
  Sinking
Pressure in solid
  Pressure is defined as force acting on unit area
  If pressure (p), force (F), and area (A), we can write the formula below
Fluids
  Pressure in fluid is produced by collisions between particles and the container.
The characteristics of liquid pressure
  Pressure in liquid increase with depth
  Pressure at one depth equally in all direction
  A liquid finds its own level in a U - tube
Pressure depend on the density of liquid.

Formula of liquid pressure
  For the information above, pressure of liquid just depend on 2 variable :
—  Depth (h),
                that have relation pressure ~ depth
—  Density (r)
                that have relations pressure ~ density
Formula of liquid pressure
  We can write formula :
p ~ r.h                  or 
p = r.g.h
which pressure (p), depth (h), density (r ), and gravitation (g)
 Pascal’s principle
  Pressure applied to an enclosed liquid is transmitted to every part of liquid, whatever the shape of liquid.
Aplication pascal’s principle
  Pascal’s principle is applied in the operation of machines that use fluids to multiply force as in hydraulic lift
Hydraulic system
  In a hydraulic system fluid is confined in two connecting chambers.
Each chambers has a piston that is free to move.
Pressure is transmitted throughout the fluid without change

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