chapter 4 summary

Work

PowerEnergy

CHAPTER 4

Work

-What is Work?-How to Calculate Work?-How to Calculate work in a gas?

NO! Work is not going to the office…

In Physics

‘ Work is done whenA forces moves to point at which it acts in the direction of the forces. ‘

Work Done = Force X Distance moved by force in the direction of the force(Joules) (Newton) (Metre)

Examples

10M

30 N50 N

Work done= 50N-20N X 10 20NX10 200 Joules toward the right.

30 degree

40N

To count the work done in an object,the force must be in the same direction in the direction they move.

So=40xcos30 X 10M

10m

(Force) (Direction)

WORK DONE IN AN EXPANDING GAS

Work Done On The Gas = Pressure X Change in Volume

When the “gas expands”,work is done by gas. (Distance is moved)If the gas “Contracts” ,then work is done on the gas.(Volume increase or decrease)

Work Done By The Gas = Force X Distance Moved(Joule)

(Joule) Pascal (Pa) Metre cube (m^3)

Newton (N) Metre (m)

ENERGYThe ability to do work.

-What is Energy?-What is Potential Energy?-What is Kinetic Energy?

What Is Energy?

-Energy is the ability to do work.

-Energy cannot be destroyed,nor created.

-Energy can only change form.

-Every move that we’re doing are consisted of Energy.

-Energy have the SI of Joule.

Potential Energy

10m

3KG

Potential energy is the ability of an object to do work as a result of its position or shape.

Potential Energy= Mass X Gravity X Height(Joule) Kilograms (Kg) 9.8 m/s^2 Metre (m)

So:EP= 3 X 9.8 X 10EP= 294 Joules

Kinetic Energy

30 Kg

Velocity= 10 m/s

Kinetic Energy is the energy due to motion.

Kinetic Energy= ½ X Mass x Velocity^2 1/2MV^2

Joules Kg (m/s)^2

So:Ek= 1/2Mv^2 ½ X 20 X 10^2 1000 Joules

Energy Conversion and Conservation

Type Of EnergyEnergy cannot be created or destroyed.It can only be converted from one form to another.

Here are a few example of the type of energy that they can be converted into:

Energy Explanation

Potential Energy Energy Due to position

Kinetic Energy Energy due to motion

Elastic or Strain Energy

Energy due to stretching an object

Electrical Energy Energy associated with moving electric energy

Sound Energy A mixture of potential and kinetic energy

Wind Energy A particular type of kinetic energy

Light Energy Energy released during chemical reaction

Solar Energy Light energy from the sun

Chemical Energy Energy released during chemical reactions

Nuclear Energy Energy associated with particle in the nuclei of atoms

Thermal Energy Sometimes called heat energy

Efficiency

What Is Efficiency ?

Efficiency gives a measure of how much of the total energy may be used and is not lost

Energy Efficiency Formula?

Efficiency = Useful Work Done/Total Energy Input X 100

The Deformation Of Solid

-Hooke’s Law-Strain Energy-Stress Energy-Young Modulus

Hooke’s Law

What is Hooke’s law?

Hooke’s law states that, provided the elastic limit is not exceeded, the extension of a body is proportional to the applied load.

Force =K.Extension

Where K is constant . It is known as elastic constant or spring constant.

Force is directly proportional to Extension

(Newton) (Metre)

Strain Energy

Strain Energy is energy stored in a body due to change of shape.

Straign Energy W = ½ K.Extension^2

Formula

Joules Metre

The Young Modulus

What is The Young Modulus?

It is a constant of a particular material which enable us to find extensions knowing the constant and the dimension of a specimen.

StrainYoung Modulus = --------------------------------

Stress

Strain = Extension/Original Length

Stress = Force/Area Normal to the force

If there is a tie,the area of the circle in the tie is the diameter.Because it is a normal to the force

The behaviour of different material under tensile stress.

Brittle Material Ductile Material

A brittle material will snap when exceeding the ultimate tensile stress.EX:Glass Fibre.

A ductile material will expand and fractured when exceeding the ultimate tensile stress.EX:Metals

The behaviour of different material under tensile stress.

ENERGY

Thermal/Heat Energy

Specific Heat Capacity

What is a specific heat capacity?It is the constant to produce an energy with a certain mass and changes in Temperature.

FormulaQ = Mass X C X Changes in temperature

Thermal (Heat) Capacity

What is a Thermal (heat) capacity?It is the quantity of the heat energy required to raise the temperature of the whole body by one degree.

Formula

Q = C X Changes in temperature

Specific Latent Heat

What is a specific Latent Heat?It is the heat energy required to convert unit mass of solid to liquid without any change in temperature.

FormulaQ = Mass X Latent heat of Fusion/Vaporisation

Latent heat of Fusion (Lf) = when Ice turns into water or water turns into Ice

Latent heat of Vaporisation (Lv) = when water turns into gas or gas turns into water.

POWER

What is Power?

Power is the rate of doing work.Power have the SI of Watt/Second.Usually Your bills in the mail,consisted of KW/H instead of W/s .

Formula

Power= Work done/Time Taken

Power=Force X Speed

Moment Of Force

Moment Of Force

What Is Moment Of Force?

It is the turning effect of a Force. ------------------------------------------

------------------------------------- F

Distance

Moment Of Force = Force x distance

Thetha

Nm N m

Couples

F

F

What is a Couple?A couple consist of two forces , equal in magnitude but opposite in direction whose lines of action do not coincide.

Moment of Force = F x 2r

r

r

The Principle of Moments

It is stated that ,for a body to be in rational equilibrium,the sum of the clockwise moments about any point must equal the sum of the anticlockwise moments about the same point.

10 m

0.1 N

20 m

0.1 N F

30 m

Sum of the clockwise moments= (10 x 0.1)Sum of the anti clockwise = (20 x 0.1) + 30F

(10 x 0.1)=(20x0.1) + 30f1=2+30fMoments= 1-2 // -30 = - 29.

Equilibrium:

What the center of Gravity?The center of gravity of an object is the point at which the whole weight of the object may be considered to act.

For a body to be equilibrium:-The sum of the forces in any direction must be zero.- The sum of the moments of the forces about any point must be zero.

Thank You