EnergyEnergy

PhysicsPhysics

EnergyEnergy

Energy comes to us from the sun.Energy comes to us from the sun.

Persons, places, and things have Persons, places, and things have energy, but we only observe the energy, but we only observe the effects of energy when something is effects of energy when something is happening.happening.

Energy can be transferred from one Energy can be transferred from one form to another and from one place form to another and from one place to another.to another.

WorkWork

The concept of force x distance The concept of force x distance is work.is work.When work is done two things When work is done two things always occur:always occur:– The application of a forceThe application of a force– The movement of something by The movement of something by

that forcethat force

Twice the load equals twice the Twice the load equals twice the work because it requires twice work because it requires twice the force.the force.Twice the distance also equals Twice the distance also equals twice the work.twice the work.

Types of WorkTypes of WorkWork falls into two general categories.Work falls into two general categories.The first category is work done against a The first category is work done against a force.force.You do work on something when you force You do work on something when you force it to move against the indulgence of an it to move against the indulgence of an opposing force. opposing force. – Ex. Pulling a bowstringEx. Pulling a bowstring

The second is work done to change the The second is work done to change the speed of an object. speed of an object. – Ex. Speeding a car up.Ex. Speeding a car up.

Units of WorkUnits of Work

The unit of measurement for work The unit of measurement for work combines a unit of force, N, with a combines a unit of force, N, with a unit of distance, m.unit of distance, m.The resulting unit of work is the The resulting unit of work is the newton-meter, or joule, named after newton-meter, or joule, named after James Joule. James Joule. One joule of work is done when a One joule of work is done when a force of 1 N is exerted over a distance force of 1 N is exerted over a distance of 1 m.of 1 m.There are also kilojoules, kJ (1000 J) There are also kilojoules, kJ (1000 J) and megajoules, mJ (1,000,000 J). and megajoules, mJ (1,000,000 J).

PowerPower

The definition of work does not include The definition of work does not include time.time.Power is the rate at which work is done. Power is the rate at which work is done. – Power = Work Done/Time IntervalPower = Work Done/Time IntervalTwice the power means twice the work can Twice the power means twice the work can be done in the same amount of time.be done in the same amount of time.The unit of power is called the watt, after The unit of power is called the watt, after James Watt.James Watt.One watt of power is expended when one One watt of power is expended when one joule of work is done in one second.joule of work is done in one second.One horsepower is equal to 0.75 kW. One horsepower is equal to 0.75 kW.

Mechanical EnergyMechanical Energy

Something that enables Something that enables an object to do work is an object to do work is energy.energy.Energy is measured in Energy is measured in joules.joules.Energy occurs in many Energy occurs in many formsformsTwo of the most common Two of the most common forms of mechanical forms of mechanical energy are:energy are:– Potential energy: energy do Potential energy: energy do

to positionto position– Kinetic energy: movement Kinetic energy: movement

of somethingof something

Potential Potential EnergyEnergy

An object may store energy by virtue of its An object may store energy by virtue of its position.position.The energy that is stored and held in The energy that is stored and held in readiness is called potential energy (PE) readiness is called potential energy (PE) because in the stored state it has the because in the stored state it has the potential for doing work.potential for doing work.– Ex. Spring or RubberbandEx. Spring or Rubberband

Chemical energy is also potential energy.Chemical energy is also potential energy.Any substance that can do work through Any substance that can do work through chemical action possesses potential chemical action possesses potential energy.energy.

Work and Potential EnergyWork and Potential EnergyWork is required to elevate objects against Work is required to elevate objects against the earth’s gravity.the earth’s gravity.

The potential energy due to elevated The potential energy due to elevated position is called gravitational potential position is called gravitational potential energy, GPE.energy, GPE.

The amount of GPE an object possess is The amount of GPE an object possess is equal to the work done against gravity in equal to the work done against gravity in lifting it or, lifting it or, – GPE = weight x height = mghGPE = weight x height = mgh– Height is the distance above some chosen Height is the distance above some chosen

reference level such as the ground. reference level such as the ground.

Kinetic EnergyKinetic EnergyIf an object is moving then it is capable of If an object is moving then it is capable of doing work.doing work.It has energy of motion, or kinetic energy, It has energy of motion, or kinetic energy, KE.KE.The kinetic energy of an object depends The kinetic energy of an object depends on the mass of the object as well as its on the mass of the object as well as its speed.speed.It is equal to half the mass multiplied by It is equal to half the mass multiplied by the square of the speed or,the square of the speed or,– Kinetic Energy = ½ mass x speedKinetic Energy = ½ mass x speed22

– KE = ½ mvKE = ½ mv22

Kinetic Energy Kinetic Energy and Workand Work

The kinetic energy of a moving object is The kinetic energy of a moving object is equal to the work required to bring it to equal to the work required to bring it to that speed from rest, or the work the object that speed from rest, or the work the object can do while begin brought to rest.can do while begin brought to rest.The equation is net force x distance = KE,The equation is net force x distance = KE,– Or Fd = ½ mvOr Fd = ½ mv22

Therefore, because speed is squared the Therefore, because speed is squared the kinetic energy is quadrupled.kinetic energy is quadrupled.

Conservation of EnergyConservation of Energy

Energy changes from one form to another.Energy changes from one form to another.It transforms without net loss or gain.It transforms without net loss or gain.The study of various forms of energy The study of various forms of energy transformations led to the law of transformations led to the law of conservation of energy.conservation of energy.The law states, “energy cannot be created The law states, “energy cannot be created or destroyed. It can be transformed from or destroyed. It can be transformed from one form to another, but the total amount one form to another, but the total amount of energy never changes.”of energy never changes.”In any system, one quantity doesn’t In any system, one quantity doesn’t change: energy.change: energy.

MachinesMachinesA machine is a device used to multiply A machine is a device used to multiply forces or simply to change the direction of forces or simply to change the direction of forces. forces.

The concept that underlies every machine The concept that underlies every machine is the conservation of energy.is the conservation of energy.

If friction and heat is neglected than, work If friction and heat is neglected than, work input should equal work output, orinput should equal work output, or– (Force x distance)(Force x distance)inputinput=(Force x distance)=(Force x distance)outputoutput

Simple MachinesSimple Machines

There are six types of simple There are six types of simple machines:machines:– The inclined planeThe inclined plane– The wedgeThe wedge– The screwThe screw– The leverThe lever– The pulleyThe pulley– The wheel and axleThe wheel and axle

WedgeWedgeThe wedge is a form of the inclined plane.The wedge is a form of the inclined plane.

A wedge is an inclined plane that moves to A wedge is an inclined plane that moves to raise an object.raise an object.

A wedge is usually a piece of wood or A wedge is usually a piece of wood or metal that is thinner at one end.metal that is thinner at one end.

The longer and thinner the wedge, the The longer and thinner the wedge, the more force it exerts.more force it exerts.

Ex. Knife or ZipperEx. Knife or Zipper

The ScrewThe ScrewThe screw is an inclined plane wrapped The screw is an inclined plane wrapped around a central bar or cylinder to form a around a central bar or cylinder to form a spiral.spiral.

A screw multiplies the force by acting A screw multiplies the force by acting through a long distance.through a long distance.

The mechanical advantage of the screw The mechanical advantage of the screw increases as the threads are closer increases as the threads are closer together.together.

Ex. Bolt and nut, and jar lidsEx. Bolt and nut, and jar lids

The Inclined PlaneThe Inclined PlaneThe inclined plane is a flat, slanted The inclined plane is a flat, slanted surface.surface.

It is a simple machine with no moving It is a simple machine with no moving parts that works by increasing the parts that works by increasing the distance over which the force is distance over which the force is exerted and thus multiplying the force.exerted and thus multiplying the force.

The most common use is probably as a The most common use is probably as a ramp. ramp.

The LeverThe LeverA lever is a rigid bar that is free to pivot, A lever is a rigid bar that is free to pivot, or move about, a fixed point.or move about, a fixed point.The fixed point is called the fulcrum.The fixed point is called the fulcrum.When a force is applied to part of the When a force is applied to part of the bar by pushing or pulling, the lever bar by pushing or pulling, the lever swings on the fulcrum and overcomes swings on the fulcrum and overcomes the resistance force.the resistance force.

Types of LeversTypes of LeversThere are three types of levers:There are three types of levers:– First class lever: Resistance force First class lever: Resistance force

and effort force are on opposite and effort force are on opposite sides of the fulcrumsides of the fulcrum

– Second class lever: the resistance Second class lever: the resistance force and effort force are on the force and effort force are on the same side with the effort force same side with the effort force further away from the fulcrum.further away from the fulcrum.

– Third class lever: the resistance Third class lever: the resistance force and effort force are on the force and effort force are on the same side with the resistance same side with the resistance force further away from the force further away from the fulcrumfulcrum

PulleyPulley

A pulley is a rope, belt or chain A pulley is a rope, belt or chain wrapped around a grooved wrapped around a grooved wheel.wheel. A pulley can function two ways: A pulley can function two ways: – Change direction of the forceChange direction of the force– Change amount of the forceChange amount of the force

A fixed pulley (attached to a A fixed pulley (attached to a stationary object) changes the stationary object) changes the direction of the effort force.direction of the effort force.A movable pulley is attached to A movable pulley is attached to the object you are trying to the object you are trying to move and thus the effort force move and thus the effort force is multiplied. is multiplied. Fixed and movable pulleys can Fixed and movable pulleys can be combined to accomplish be combined to accomplish even more work. even more work.

Wheel and AxleWheel and Axle

A wheel and axle is a simple machine A wheel and axle is a simple machine made up of two circular objects of made up of two circular objects of different sizes.different sizes.The wheel is the larger object and it turns The wheel is the larger object and it turns about the smaller object called the axle.about the smaller object called the axle.Because the wheel is larger, force is Because the wheel is larger, force is multiplied when it is applied to the axle.multiplied when it is applied to the axle.The mechanical advantage depends on The mechanical advantage depends on the radius of the wheel and axle systems. the radius of the wheel and axle systems. Ex. Screwdriver, Ferris WheelEx. Screwdriver, Ferris Wheel

Mechanical AdvantageMechanical Advantage

The ratio of output force to input The ratio of output force to input force for a machine is called the force for a machine is called the mechanical advantage.mechanical advantage.

Neglecting friction, the mechanical Neglecting friction, the mechanical advantage can also be determined advantage can also be determined by the ratio of input distance to by the ratio of input distance to output distance. output distance.

EfficiencyEfficiencyAn ideal machine would be 100% An ideal machine would be 100% efficient.efficient.However, in any machine, some However, in any machine, some energy is transformed into atomic or energy is transformed into atomic or molecular kinetic energy aka heat. molecular kinetic energy aka heat. Efficiency will always be less than Efficiency will always be less than one. one. Efficiency is expressed as,Efficiency is expressed as,– Useful work output/total work outputUseful work output/total work output

Rube Goldberg Rube Goldberg Rube Goldberg was a Jewish American Rube Goldberg was a Jewish American cartoonist who became famous for his cartoonist who became famous for his Rube Goldberg machines.Rube Goldberg machines.He drew cartoons for the many He drew cartoons for the many newspapers including the New York newspapers including the New York Evening Journal and won the Pulitzer Prize Evening Journal and won the Pulitzer Prize in 1948.in 1948.Rube Goldberg machines were developed Rube Goldberg machines were developed to poke fun at the way useful devices are to poke fun at the way useful devices are supposed to make life easier.supposed to make life easier.

Rube Goldberg MachinesRube Goldberg Machines

A Rube Goldberg machine is an A Rube Goldberg machine is an exceedingly complex machine that exceedingly complex machine that performs a simple task in a performs a simple task in a convoluted way.convoluted way.

In 1987, Purdue University began the In 1987, Purdue University began the National Rube Goldberg machine National Rube Goldberg machine contest in which college teams build contest in which college teams build machines around a simple theme.machines around a simple theme.

An ExampleAn Example

The TaskThe TaskYour task is to build a Rube Goldberg Your task is to build a Rube Goldberg machine to complete the simple task of machine to complete the simple task of making a cup of coffee.making a cup of coffee.Your machine must be small enough to fit Your machine must be small enough to fit through the classroom door and complete through the classroom door and complete the task in less than nine minutes.the task in less than nine minutes.You must use at least 15 steps to You must use at least 15 steps to complete the task and use each of the six complete the task and use each of the six simple machines.simple machines.You will also have to submit a drawing and You will also have to submit a drawing and written description of your machine written description of your machine outlining each energy transfer.outlining each energy transfer.