Chapter 4 Work
- 1. CHAPTER 4 Work, Energy, and Power
- 2. WORK Work is done when a force moves an object to which it acts in the direction of the force Work = force x distance moved by force in the direction of the force Unit of work = Joule (J) or (force in newton x distance moved in metre)
- 3. WORK DONE BY EXPANDING GAS As gas expands, it does work by breaking down the masonry. Work done = pressure x change in volume When gas expands, work is done by the gas. If the gas contracts, then work is done on the gas. Unit of work (J) = pressure (pascals/Pa) x changes in volume (m3)
- 4. ENERGY Energy is the ability to do work Energy Notes Potential energy Energy due to position Kinetic energy Energy due to motion Elastic or strain energy Energy due to stretching of an object Electrical energy Energy associated with moving electric charge Sound energy A mixture of potential and kinetic energy of the particles in the wave Wind energy A particular type of kinetic energy Light energy Energy of electromagnetic wave Solar energy Light energy from the sun Chemical energy Energy released during chemical reaction Nuclear energy Energy associated with particles in the nuclei of atoms Thermal energy Sometimes called heat energy
- 5. ENERGY Potential energy is the ability of an object to do work as a result of its position or shape Work done = force x distance moved = mxgxh m- mass g- gravitational force h- height of the distance moved
- 6. ENERGY Kinetic energy is energy due to motion. Ek=½mv2 m- mass v- velocity
- 7. ENERGY CONVERSION AND CONSERVATION Law of energy conversation: Energy cannot be created or destroyed. It can only be converted from one form to another.
- 8. EFFICIENCY Efficiency gives measure of how much total energy may be used and is not ‘lost’ Efficiency = useful work done ÷ total energy input
- 9. DEFORMATION OF SOLIDS Deformation – change of shape tensile Deformation compressive Tensile – stretching of an object Compressive- pressing of an object
- 10. HOOKE’S LAW Hooke’s law stated that proved the elastic limit is not exceeded, the extension of a body is proportional to the applied load. F= kΔL F- force k – elastic constant (Nm-1) ΔL- extension
- 11. STRAIN ENERGY Strain energy is the energy store in a body due to change of shape Strain energy W= ½k(ΔL)2 or W= ½kx2
- 12. THE YOUNG MODULUS Young modulus is the constant that a particular material has that enable us to find extensions knowing the constant and the dimension of the speciment. Young modulus is = Stress ÷ Strain
- 13. STRAIN Strain is the ratio of two lengths, the extension and the original, and thus it does not have unit. Stress= extension ÷ original length
- 14. STRESS The strain produced within an object is caused by stress. Tensile stress is the changes in length of the object Stress= Force ÷ area normal to force The unit of stress is (Nm-2) also known as Pascal (Pa)
- 15. SPECIFIC HEAT CAPACITY Specific heat capacity is the numerical value which a substance needed to raise the temperature of unit mass of substance by one degree. Q= mcΔt Q- heat m- mass c- specific heat capacity Δt- temperature change
- 16. THERMAL CAPACITY Thermal capacity is the numerical value of a body needs to raise the temperature of the whole body by one degree Q=CΔt Q- heat energy C- thermal capacity
- 17. SPECIFIC LATENT HEAT Specific latent heat is the numerical value of the quantity of heat energy required to convert unit mass of solid to liquid (fusion) or liquid to gas (vaporization) without any change in temperature. Q=mL L – specific latent heat
- 18. EXCHANGES OF HEAT ENERGY Law of conservation of energy stated that energy applies in heat energy gained by the colder object is equal to heat loss by the hotter object. Energy gained= Energy lost
- 19. POWER Power is the rate of doing work and it’s a scalar quantity Power = work done ÷ time taken Power= force x speed Unit of power is watt
- 20. KILOWATT HOUR One kilowatt hour is the energy expended when work is done at the rate of 1 kilowatt for a time of 1 hour.
- 21. MOMENT OF A FORCE The turning effect of a force is called moment of force The moment of force is defined as the product of the force and the perpendicular distance of line of action of the force from the pivot.
- 22. COUPLES A couples consist of two forces equal in magnitude but opposite in direction of whose lines of action do not coincide. The torque of a couple is the product of one of the forces and the perpendicular distance between the forces.
- 23. PRINCIPLE OF MOMENT The principle of moment stated that for a body to be in rotational equilibrium, the sum of the clockwise moment about any point must equal the sum of anticlockwise moment about the same point.
- 24. CENTRE OF GRAVITY The centre of gravity of an object is the point at which the whole weight of the object may he considered to act.
- 25. EQUILIBRIUM Equilibrium : • Sum of all forces in any direction must be 0 • Sum of moment of the forces about any point must be 0
- 26. RESOURCES International A/AS Level Physics by chris mee, mike crundell, brian arnold, and wendy brown, published at 2008.
- 27. THE END Jessica L Grade 11 - Sci