2 Energy Examples of energy. When we consider the quantity force X distance, we are talking about work.Two things enter into every case where work is done. 1) the application of a force and 2) the movement of something by that force.Work = force x distance or W = FdWork falls in two categoriesThe unit of measurement for work combines a unit of force, N, with a unit of distance being M, the result of this is a joule.
3 Power Some examples of power Power is the rate at which work is done. It equals the amount of work done by dividing the time interval during which the work is done.Power = work done over time intervalThe unit of power is joule per second, also known as the watt, in honor of James Watt.
4 Mechanical Energy Some examples of mechanical energy Energy enables an object to do workMechanical energy- the energy due to position of something, or the movement of somethingMechanical energy can be in the form of either potential energy or kinetic energy, or the sum of the two.
5 Potential energy Some examples of potential energy An object may store energy by virtue of its positionThe energy that is stored is called potential energyChemical energy in fuels is also potential energyWork is required to elevate objects against the earth’s gravityThe potential energy due to elevated positions is called gravitational energyGravitational potential energy = weight x heightPE = mgh
6 Kinetic energy Some examples of kinetic energy If an object is in moving, then it is capable of doing workIt has energy of motion, or kinetic energyThe kinetic energy of an object depends on the mass of the object as well as its speedKinetic energy = ½ mass x speed squaredNet force x distance = kinetic energyFd = ½ mv squaredWhenever work is done, energy changes. This is the work-energy theorem
7 Conservation of energy Some examples of conservation of energyThe study of the various forms of energy and the transformation from one form into another led to one of the greatest generalizations in physics—the law of conservation of energyEnergy cannot be created or destroyedIt can be transformed from one form to anotherThe welding of an atomic nuclei is called thermonuclear fusion and will be covered later.
8 Machines Some machines A machine is a device used to multiply forces or simply to change the direction of forcesWhen we do work on the end of a lever, the other end does not work on the load(force x distance) input = (force x distance) outputThe pivot point is also known as the fulcrumThe ratio of the output force to the input force for a machine is the mechanical advantageA pulley is basically a kind of lever that can be used to change the direction of a force.
9 Efficiency Some examples of efficiency An ideal machine would have 100% efficiencyIn any machine, some energy is transformed into atomic or molecular kinetic energy– making the machine warmerEfficiency can be expressed at the ratio of useful work output to total work inputEfficiency = useful work output divided by total work inputEfficiency = actual mechanical advantage divided by theoretical mechanical advantage
10 Energy for life Some examples of energy for life Every living cell in every organism is a machine. Like any machine, living cells need an energy supplyOnly green plants and certain one-celled organisms can make carbon dioxide to combine with water to produce hydrocarbon compounds such as sugar. This process is known as photosynthesis and requires an energy input which normally comes from the sun
11 Review of chapter Some simple machines ETC. When a constant forces moves and object in the direction of the force, the work done equals the product of the force and the distance the object is movedPower is the rate at which work is doneThe energy of an object enables it to do workMechanical energy is due to the position of something (potential energy) or the movement of something (kinetic energy)
12 Review of Chapter, Continued Some simple machinesThe law of conservation of energy states that energy cannot be created or destroyedEnergy can be transformed from one form to anotherA machine is a device for multiplying force or changing the direction of forceThe lever, pulley, and inclined plane are simple machinesThe useful work output of a machine is less than the total work input