Objectives:• To cite examples of forces encountered in day to day activities• To describe and discuss the four fundamental forces• To state the scientific definition of work and solve work problems• To describe the different forms and transformations of energy• To explain how energy is related to work
ForceForce - push or pull contact forces – exerted between objects that are in close contact noncontact forces – can be exerted between objects that are not even touching
Fundamental forces• Gravitational force - affects anything that has mass• Electromagnetic forces – exerted on charged objects or magnetic objects Like charges repel, unlike charges attract. Like poles repel, unlike poles attract.• Weak force – exerted between leptons and hadrons; active only at distances less than 10-18 m• Strong forces – acts only on hadrons; strongest of the four but effective only at very short separations (10-15m)
WorkWork - product of the force and displacement (displacement – distance moved by an object as a result of the force’s action) - being done when all of the following conditions are satisfied a. A force is exerted on the object. b. The object moves. c. The motion is in the direction of the force.
WorkSample problem 1:How much work is done when a 100-N cart ispulled over a distance of 1 meter?Given: F = 100N d = 1mFind: WSolution: W = Fd W = 100N(1m) = 100Nm or 100J
WorkTo get the maximum amount of work , theforce must be parallel to the motion.
WorkThe perpendicular component of the forcedoes no work, if there is no motion in thatdirection .
Work: Sample problem 2 A box having 2 kg mass, under the effect of forces F1, F2, and F3, takes distance 5 m. Which of the forces do work? What is the work done by that force? W3 = F3d = 30N(5m) = 150J
PowerPower – refers to the rate at which work is done P = Wdone/timeUnit of power:• joule/second (J/s) 1J/s = 1 watt (W)• Horsepower (hp) 1hp = 746 W - used to specify the power output of motors and engine
MachineMachine – a device that transfers a force from its point of application to some other point to where it is used - may multiply force or distance or simply change the direction of the force
Simple MachinesSix Simple Machines1. Lever – a rigid object that is free to rotate about a fixed point called the fulcrum2. Wheel and axle – rotating lever consisting of a large wheel attached to a smaller axle, which is just a rod or cylinder3. Pulley – modified lever; grooved wheel that is free to turn about an axle
Simple MachinesSix Simple Machines4. Inclined plane – a flat surface with one end placed higher than the other5. Wedge – two inclined planes set back to back6. Screw – an inclined plane that is wound around a cylinder
Concept of EnergyEnergy - capacity to do work• If something has energy it can do work.• If something can do work, then it has energy.• Work and energy have the same unit, (joule,J)• It cannot be seen but evidences prove its existence.
Different Forms of EnergyPotential Energy (PE)- stored energy due to the object’s position or internal arrangement of moleculesKinetic Energy (KE)- energy of moving object
Different Forms of Potential Energy1. Gravitational potential energy - energy is due to the object’s position or height from the earth The higher the position, the greater is the gravitational PE2. Magnetic potential energy - energy from magnets3. Chemical energy - energy due to the arrangement of the atoms and molecules in matter
Different Forms of Kinetic Energy1. Electrical Energy – due to the motion of charged particles through conducting wires2. Nuclear Energy – energy derived from the nuclear reaction nuclear fusion – nuclei join to form a nucleus nuclear fission – nucleus is broken into smaller nuclei3. Radiant Energy – energy transported by electromagnetic waves4. Thermal Energy - sum of the KE’s of the molecules due to their linear motion
Energy TransferHeat can be transferred through• Radiation – transfer by rays or electromagnetic waves• Conduction – transfer by direct contact• Convection - transfer involving difference in density
Energy transformationEnergy cannot be created nor destroyed, itcan only be transformed from one form toanother. (Law of Conservation of Energy)• Electrical energy chemical energy• Chemical energy electrical energy• Radiant energy chemical energy
Sources of Energy• Renewable sources- energy sources that can be replenished• Nonrenewable sources- energy sources that has undergone long process of formation
Sources of Energy – Renewable Sources• Geothermal energy - heat energy from deep within the earth• Hydropower - energy from moving water• Tidal energy - energy from the regular rise and fall of sea water• Wind energy - energy from wind mills• Solar energy - energy rom the sun• Biomass – energy resource that is derived from plant or animal matter
Sources of Energy – Nonrenewable Sources• Fossil fuels - derived from the remains of plants and animals that died millions of years ago petroleum – also called crude oil; complex mixture of hydrogen and carbon compounds coal – most abundant and dirtiest fossil fuel natural gas – mainly methane and the cleanest of all the fossil fuels• Nuclear energy – energy from fission or fusion reaction
Problems Related to Energy1. Combustion of fossil fuels release gases and solid pollutants that are harmful to living and non-living things.2. Nuclear energy production a) release radioactive substances harmful to living things b) waste disposal c) poses risk of reactor accidents d) causes thermal pollution3. Tidal and hydroelectric dams create ecological froblems.4. geothermal energy emits H2S
Energy Utilization and Consumption• All people are users of energy.• Energy sources are popularly used for the generation of electricity• Factors that will affect the selection of energy for electricity include - availability in the country - cost of production - availability of local manpower to make and repair the plant - ecological impact during extraction, utilization and waste disposal
Energy conservation- refers to the practice of extending the useful life of the earth’s energy resources- should be taught early in life- influenced by the people’s attitudes, mores and beliefs
References• McLaughlin, Charles W., Thompson, Marilyn, and Zike, Dinah. (2012). Glencoe Physical Science. McGraw-Hill Education• Serway, Raymond A., Vuille, Chris and Faugnn, Jerry S.(2009). College Physics (Volume 2) 8th ed. Brooks/Cole Cengage Learning• Tillery, Bill W. (2011). Physical Science McGraw- Hill Publishing Co.