Forms of Energy – Part II

Forms of Energy

Mechanical

Electrical

Chemical

Nuclear

Thermal/Geothermal

Sound

Seismic

Radiant

Kinetic and Potential Energies Combined

Mechanical Energy – The sum of potential energy and kinetic energy in a system of objects.

The energy an object has because of a combination of the following:

1. The movement of its parts (kinetic energy)

2. The position of its parts (potential energy)Example: Opening a door

•Potential Energy – the energy stored in the person•Kinetic Energy – lifting my hand to push the door•Mechanical Energy – my PE and KE were transferred into mechanical energy which caused work to be done (the door opens).

Mechanical Energy

How could a bowling ball have mechanical energy?

•PE – bowling ball has mass and the PE increases as you pull it back.

•KE – release the bowling ball as it moves down the lane.

Because of its mechanical energy it is able to do work on the pins!

Can you give some examples of mechanical energy?

Thermal Energy

Thermal Energy – The sum of the kinetic energy and potential energy of the particles that make up an object

Cannot always be seen.

Individual vibrate back and forth in place, giving them .

The particles also have because of the between particles and the of the particles.

particleskinetic energy potential

energydistance

charge

Thermal Energy

As the water heats up to make a cup of coffee the particles begin to increase kinetic energy (velocity of particles) and increase potential energy (distance between particles increases) resulting in an increase of thermal energy.

Thermal Energy in the Earth

The particles in Earth’s interior contain great amounts of thermal energy.

This type of energy is calledgeothermal energy

Hot rocks underground heat water to produce steam. We drill holes down to the hot region, steam comes up, is purified and used to drive turbines, which drive electric generators.

Geothermal Energy Advantages

Does not produce any pollutionPower stations do not take up much room, therefore there is not much environmental impactNo fuel is neededOnce you've built a geothermal power station, the energy is almost free. (It may need a little energy to run a pump, but this can be taken from the energy being generated. )IF IT’S SO GREAT, WHY DON’T WE USE IT!?

•There aren’t many places you can build a power station•You need specific rocks that can be drilled into and at a depth you can drill down to.

Types of Kinetic EnergyAt this point you know that anything in motion has kinetic energy, including:

Large objects that you can seeSmall particles that you cannot see (molecules, ions, atoms, and electrons)

Electric EnergyElectric Energy – The energy caused by the movement of electrons.

Can be easily transported through power lines and transformed into other forms of energy. Electrons move around the nucleus of an atom and they can move from one atom to another.When electrons move, they have kinetic energy and create an electric current.

Types of Potential Energy

Potential energy – stored energy that depends on:

Position or shape of an object.

Chemical Energy – energy that is stored in and released from the bonds between atoms.

Most electric energy (a type of kinetic) comes from fossil fuels such as

The atoms that make up fossil fuels are joined by

petroleum, natural gas, and coal.

chemical bonds

Chemical Energy

Chemical Energy

When fossil fuels burn, the between atoms that make up the fossil fuel

.

When this happens, transforms into

chemical bondsbreak

apartchemical energythermal energy.

What are some other forms of Chemical

Energy?

The chemical energy in food is released while the food is being digested and the molecules of food are broken down into smaller pieces. As the bonds between the atoms of the food break or loosen, new substances are created as a result of the chemical reactions taking place.

Inside the battery, a reaction between the chemicals takes place. But reaction takes place only if there is a flow of electrons. Batteries can be stored for a long time and still work because the chemical process doesn't start until the electrons flow from the negative to the positive terminals through a circuit.

Air activated hand warmers contain various chemicals. As the disposable packet is opened, oxygen crosses the permeable cover and reacts with iron, in the presence of catalyst salt and water. The production of Fe2O3 is an exothermic reaction, generating heat typically between 1 and 10 hours.

Nuclear Energy

Nuclear Energy – energy stored in and released from the nucleus of an atom.

Majority of energy on Earth comes from

and release nuclear energy.

Nuclear Fusion –

Nuclear Fission -

Nuclear fusion

nuclear fission

A process that occurs in the sun which joins the nuclei of atoms and releases large amounts of energy.Nuclear energy plants on Earth break apart the nuclei of certain atoms.

the Sun

Energy from Waves

Wave – a disturbance that carries energy from one place to another.

Waves move , NOT matter.energy

WAVELENGTH

CREST

TROUGH

AMPLITUDE

Energy from Waves – Sound Energy

Sound Energy – the form of energy associated with the vibration or disturbance of matter

Some animals emit sound waves to find their prey.

For example: Bats – the amount of time it takes sound waves to travel to their prey and echo back tells the bat the location of the prey it’s hunting.

Energy from WavesSeismic Energy – is the energy transferred by waves moving through the ground.

Earthquake’s occur when Earth’s suddenly position.

The of plate movement is carried through the ground by

Seismic WavesBody waves –

Surface waves -

tectonic platesshift

kinetic energyseismic waves

travel through interior of Earth. P (primary) waves – fastest and first to arrive. S (secondary) wave slower, and arrives after p wave.

travel through Earth’s crust – responsible for damage associated with earthquakes.

How is Seismic Energy Measured?

Seismograph – an instrument for measuring seismic waves (earthquakes).

Consists of a frame and a mass that can move relative to it. When the ground shakes, the frame vibrates as well while the mass tends not to move due to inertia. The difference in movement between the frame and the mass is amplified and recorded electronically.

Measure:Magnitude: size of earthquake

Depth: how deep the earthquake is

Location: where the earthquake occurred.

Energy from WavesRadiant Energy – the energy carried by electromagnetic waves.

Electromagnetic waves – electric force (example: shock you get when you touch a metal doorknob) and magnetic force (example: the pull that attracts metals to magnets) that move perpendicular to each other to bring on an electric field around them.

Can travel through solids, liquids, gasses and vacuums.

There are several different kinds of electromagnetic waves – each with different wavelengths, properties, frequencies and power. The entire wave system is called” the electromagnetic spectrum.

Electromagnetic spectrum – the range of all possible frequencies of electromagnetic radiation.

The relationship between energy and wavelength:

The the wavelength the the energy.The the wavelength the the energy.

The wave with the highest frequency is:

The wave with the lowest frequency is:

shorter greater

longer weaker

gamma rays

radio rays

What’s the difference?

What is the difference between an energy TRANSFER and an energy TRANSFORMATION?

Energy Transfer –

Energy Transformation -

When energy moves from one object to another without changing its form

When one form of energy is converted to another form of energy.

Energy Transfers and Transformations

In every energy transfer and transformation some energy is transformed into thermal energy.

In every transformation such as electric to sound there is always thermal energy being transferred to surroundings.

Transfer or Transformation?

TransferredEnergy

TransformedEnergy

Type(s) of EnergyBeing Transferred

or Transformed1.A tennis racket

applies force to atennis ball when ithits the ball, forcingthe ball to moveforward.

2.A softball playerthrows a balltoward first base.

3.Fuel in an engineburns, and the carmoves forward.

4.A runner eats anenergy bar and later that day runs in the100-m race.

Transfer or Transformation?

5.Lights glow in thenight sky when thepower switch isturned on.

6.A hockey stick stopsa sliding puck andsends it toward thegoal.

7.A truck roars by arow of apartmentson a quiet evening.

8.A song plays on theradio.

Plants and The Body

Plants carry out a process called

How is photosynthesis an energy transformation?

photosynthesis

Plants use radiant energy (light from Sun) to transform water and CO2 into Sugar and Oxygen. Sugar is used as food for the plant and the oxygen is released into the air we breathe.

Types of Kinetic Types of Potential   

Both Kinetic and Potential

Energy and WorkWork – the transfer of energy that occurs when a force makes an object move in the direction of the force.

Force- push or pull on an object

For example: The student does work on the drums when he lifts them. Once the drums are in place, no work is being done.With your partners at

your table you have 1minute to come upwith 3 examples of work using thisdefinition.

1. A scientist delivers a speech to an audience of his peers.

2. A body builder lifts 350 pounds above his head.

3. A mother carries her baby from room to room.

4. A father pushes a baby in a carriage.

5. A woman carries a 20 kg grocery bag to her car?

NO

YES

NO

YES

NOLets take a closer look at #3 and #5. Think about the definition – why are these two examples NOT considered work?

#3 – the force is applied upward to hold the baby, however the baby moves in a horizontal position with its mother. Therefore the mother is NOT doing work upon the baby.

#5 – the force is applied upward to the grocery bag, however the grocery bag moves in a horizontal position with the woman. Therefore the woman is NOT doing work on the bag

What’s Work?

WorkWork is done only while the force is moving the object (in the direction that the force is being applied).

Work also depends on:

Joules – the unit of energy and work

*Named After: James Prescott Joule – conducted experiments measuring the amount of work needed to create a given amount of heat.

The distance an object moves during the time the force is applied.

Calculating Work

Work = Force x distance

Abbreviation

Unit

Work W J (Joules) = 1kg x m2/s2

Force F N (Newtons) = 1kg x m/s2

Distance

d m (meters) = m

Sample Problem 1

A student lifts a bag from the floor to his shoulder 1.2 meters above the floor, using a force of 50N. How much work does the student do on the bag?

Sample Problem 2

Nicole lifts a flower pot onto a shelf 3 meters high, using a force of 30N. How much work is done to place the flower pot onto the shelf?

Power is the rate at which work is done.

Power = Work/Time

The unit of power is the watt.Watt – equivalent to 1 Joule (work) per second (time)

POWER

35

Check for Understanding

1.Two physics students, Ben and Bonnie, are in the weightlifting room. Bonnie lifts the 50 kg barbell over her head (approximately .60 m) 10 times in one minute; Ben lifts the 50 kg barbell the same distance over his head 10 times in 10 seconds.

Which student does the most work?

Which student delivers the most power?

Explain your answers.

Ben and Bonnie do the same amount of work; they apply the same force to lift the same barbell the same distance above their heads.

• Yet, Ben is the most powerful since he does the same work in less time.

• Power and time are inversely proportional.

 

2. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s2 a distance of 10 meters in 5 seconds? This problem requires you to use the formulas for force, work, and power all in the correct order.

Force=Mass x Acceleration

Work=Force x Distance

Power = Work/Time

2. How much power will it take to move a 10 kg mass at an

acceleration of 2 m/s2 a distance of 10 meters in 5 seconds? This

problem requires you to use the formulas for force, work, and

power all in the correct order.

Force=Mass x Acceleration

Force=10 x 2

Force=20 N

Work=Force x Distance

Work = 20 x 10

Work = 200 Joules

Power = Work/Time

Power = 200/5

Power = 40 watts

Energy and Heat

In every energy transformation and every energy transfer, some energy is transformed into thermal energy.

Thermal energy – the sum of kinetic and potential energy of the particles that make up an object. (Example: Friction)

When thermal energy is moving from a region of higher temperature to a region of lower temperature it is called heat.

Scientists sometimes call this heat because

waste energyit is not easily used to do

useful work.

Machines

Machines transfer

Simple Machines – machines that do work using one movement.

Simple machines do not change the amount of required to do a task; they only change the

mechanical energy

workway work is done

Simple MachinesInclined plane- a flat, sloped surface that makes it easier to move an object from a lower to a higher elevation..

Screw – a modified version of an inclined plane. The threads of the screw are a type of circular ramp (inclined plane)

Simple Machines

Wedge – a modified inclined plane. Used to separate or hold devices.

Lever – a simple machine that pivots around a fixed point (fulcrum).

Simple Machines

Wheel and Axle – a shaft attached to a wheel of a larger diameter so that both rotate together.

Pulley – a grooved wheel with a rope or cable wrapped around it.

Machines and Work

The work you do on a machine is called the

The work the machine does on an object is the

Machines make work easier by changing the the object moves or the

required to do work on an object

*remember – work is the product of force and distance.

input work.

output work.

distanceforce

Complex Machines

Complex Machines – two or more simple machines working together.

Efficiency

Efficiency - the ratio of output work to input work.

We express efficiency by

Efficiency equation:

Efficiency is a measure of how much work put into the machine is changed into useful output work using a percentage.

x 100

x 100

Efficiency

The efficiency of a machine is

Some work is always transformed into because of

How could we improve efficiency of a machine?

NEVER 100%

wasted thermal energyfriction

Reduce the wasted thermal energy by reducing friction. We couldreduce friction by oiling the different parts of the machine.

A light bulb uses 120 J of electrical energy and produces 48 J of light energy. Calculate the

percent efficiency of the light bulb.

x 100

Calculate the percent efficiency of an electric motor that uses 15,000 J of energy to produce

11,500 J of useful energy

x 100

Calculate the percent efficiency of an incandescent light bulb that produces 2,500 J of light energy from 50,000 J of electrical energy.

x 100

1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth.

2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec?

3. Using a single fixed pulley, how heavy a load could you lift?

Practice Questions

4. Give an example of a machine in which friction is both an

advantage and a disadvantage.

5. Why is it not possible to have a machine with 100% efficiency?

6. What is effort force? What is work input? Explain the

relationship between effort force, effort distance, and work

input.

Practice Questions

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1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth. Work is defined as a force applied to an object, moving that object a distance in the direction of the applied force. The bricklayer is doing more work.

2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec? Work = 7 m X 50 N X 2 = 700 N-m or J; Power = 700 N-m/20 sec = 35 W

3. Using a single fixed pulley, how heavy a load could you lift?Since a fixed pulley has a mechanical advantage of one, it will only change the direction of the force applied to it. You would be able to lift a load equal to your own weight, minus the negative effects of friction.

Practice Questions

4. Give an example of a machine in which friction is both an advantage and a disadvantage. One answer might be the use of a car jack. Advantage of friction: It allows a car to be raised to a desired height without slipping. Disadvantage of friction: It reduces efficiency.

5. Why is it not possible to have a machine with 100% efficiency? Friction lowers the efficiency of a machine. Work output is always less than work input, so an actual machine cannot be 100% efficient.

6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input. The effort force is the force applied to a machine. Work input is the work done on a machine. The work input of a machine is equal to the effort force times the distance over which the effort force is exerted.

Practice Questions

Newton’s Laws and Simple Machines

Recall and define each of Newton’s Laws of Motion

How could we relate these laws to machines?

1st Law – an object in motion will stay in motion and an objectat rest will stay at rest unless acted on by an unbalanced force.2nd Law – the acceleration of an object is equal to the object’s netforce divided by the objects mass.3rd Law – every action has an equal and opposite reaction.

Newton’s 1st Law and Machines

Newton’s 1st Law tells us that the motion of an object changes when the forces that act on the object are

When you pull a hammer handle, the claws of the hammer apply a force on the nail. The hammer is acting as an that causes the nail to go from to .

unbalanced.

unbalanced forcerest motion

Newton’s 2nd Law of Motion

Newton’s 2nd Law gives us the relationship between

Again, using the hammer as a lever applies to Newton’s 2nd Law because the more you apply to the hammer to remove the nail the quicker the nail will out of the piece of wood.

force, mass and acceleration

forcemove (accelerate)

Newton’s 3rd Law of Motion

Newton’s 3rd Law says that if one object applies a force on a second object, the second object will apply an equal force in the opposite direction.

For example, when you have a hammer being used as a to pull out a nail, you apply force on the hammer. The hammer applies

This is an

lever

an equal force in the opposite direction (back on you).

action-reaction force