EfficiencyEfficiency

Measure of how much work is put to “good use”

Measure of how much work is put to “good use”

Efficiency of MachinesEfficiency of Machines Law of C of E says that energy in must

equal energy out However, often a lot of energy is lost

Heat, friction, sound, etc.

Efficiency equals (Useful energy out) *100% (Energy in) Higher the percentage….the more efficient

the machine is

Law of C of E says that energy in must equal energy out However, often a lot of energy is lost

Heat, friction, sound, etc.

Efficiency equals (Useful energy out) *100% (Energy in) Higher the percentage….the more efficient

the machine is

Efficiency (cont.) Efficiency (cont.) Companies seek to find most efficient machines

to manufacture, transport, and develop Ex. Gas powered cars are not very efficient,

about 10 - 25% efficient Electric (hybrid) cars--much more efficient

Get up to 3 times the mileage of some gas cars

http://auto.howstuffworks.com/hybrid-car4.htm Government standards

Companies seek to find most efficient machines to manufacture, transport, and develop

Ex. Gas powered cars are not very efficient, about 10 - 25% efficient Electric (hybrid) cars--much more efficient

Get up to 3 times the mileage of some gas cars

http://auto.howstuffworks.com/hybrid-car4.htm Government standards

100% Efficient100% Efficient

ProblemProblem

http://www.bbc.co.uk/schools/gcsebitesize/physics/energy/energyefficiencyrev3.shtml

http://www.bbc.co.uk/schools/gcsebitesize/physics/energy/energyefficiencyrev3.shtml

Question 1Question 1 A power plant burns 75kg of coal every second. Each kg of coal

contains 27 MJ (27 million joules) of chemical energy. What is the energy output of the power station every sec?

The Solution

= 75 x 27 million J per sec = 2025 million J per sec

= 2025 million J/s or (2025 megaWatts)

A power plant burns 75kg of coal every second. Each kg of coal contains 27 MJ (27 million joules) of chemical energy.

What is the energy output of the power station every sec?

The Solution

= 75 x 27 million J per sec = 2025 million J per sec

= 2025 million J/s or (2025 megaWatts)

Question 2Question 2 The electrical power output of the power plant

is 800MW (800 million watts). But Question 1 stated that the chemical energy output of the station was 2025 MW…..So, What has happened to the rest of the energy?

The Answer

Most of the rest of the energy is wasted as heat - up the chimney of the power station, in the cooling towers, and because of friction in the machinery.

The electrical power output of the power plant is 800MW (800 million watts). But Question 1 stated that the chemical energy output of the station was 2025 MW…..So, What has happened to the rest of the energy?

The Answer

Most of the rest of the energy is wasted as heat - up the chimney of the power station, in the cooling towers, and because of friction in the machinery.

Question 3Question 3 Calculate the efficiency of the power plant

as a percentage.

The Solution Efficiency = useful power output/total power input

= 800,000,000 W/2025,000,000 W

= 0.395 x 100% to create a percentage = 39.5%

Calculate the efficiency of the power plant as a percentage.

The Solution Efficiency = useful power output/total power input

= 800,000,000 W/2025,000,000 W

= 0.395 x 100% to create a percentage = 39.5%

Simple MachinesSimple Machines wedge, pulley, lever, ramp,

screw, wheel and axle Multiply force but applying

small force over greater distance

Amount of work done is not increased by a machine

By law of conservation of energy it is impossible to multiply energy

wedge, pulley, lever, ramp, screw, wheel and axle

Multiply force but applying small force over greater distance

Amount of work done is not increased by a machine

By law of conservation of energy it is impossible to multiply energy

A screw applies a small force over the long distance across the face of all of its threads at once to accomplish the same work as a large force over a small distance

Mechanical AdvantageMechanical Advantage Usefulness of machines is due to

multiplication of force, not of energy Often limited by how much force we

can apply, so we apply a small force over a large distance

One way to measure how useful a simple machine is is by measuring its Ideal Mechanical Advantage

MA = Force output / force input

Usefulness of machines is due to multiplication of force, not of energy Often limited by how much force we

can apply, so we apply a small force over a large distance

One way to measure how useful a simple machine is is by measuring its Ideal Mechanical Advantage

MA = Force output / force input

By applying a 10 N force and moving this end 50 cm..

You were able to apply a 100 N force on this end and move the heavy rock 5 cm

Soo….MA = 10/1 = 10

Incline PlaneIncline Plane

MA is made up by comparing the Parallel force by the force of gravity, on any incline the parallel force will be much less than the weight of the object, this is why it is easier to walk long distance on low incline than a short distance and a steep incline or climbing straight up

MA is made up by comparing the Parallel force by the force of gravity, on any incline the parallel force will be much less than the weight of the object, this is why it is easier to walk long distance on low incline than a short distance and a steep incline or climbing straight up

Schober Brothers

embark on a hike in

Yosemite Ntnl. Park

Schober Brothers

embark on a hike in

Yosemite Ntnl. Park

…..And learn a harsh lesson about Incline Planes…

Day 1, short hike…little wet…. feelin good.

This is easy!!Idiots!

Day 2 Hike -- 2600 ft of vertical climb to top of Yosemite Falls

Day 2 Hike -- 2600 ft of vertical climb to top of Yosemite Falls

2600 vertical feet

Hike on Day 2-- In pain, not even close to the top

Hike on Day 2-- In pain, not even close to the top

Me slumped on a rock about to vomit…. …………………Will cant feel his legs

Andy takes picture and laughs

Little higher up the mountain….

Get to the top ..Exhausted…. Pass out on a rock while squirrel eats our granola

Get to the top ..Exhausted…. Pass out on a rock while squirrel eats our granola

The Point…The Point…Activity Difficulty Who can do it Why??

Hike on flat ground Easy Anyone with 2 legs Horizontal motion, do not need to work against gravity

Hike up mountain via long switchbacks and low grade paths

Harder Anyone with 2 legs and are at least a little bit in shape(Day 1 Hike)

Working against gravity to gain PE but spread out over a long distance. Longer distance means shorter Force. Also spread out over long amt. of time

Hike up mtn. via steep steps with high incline

Very Difficult

Andy, 8 year old girls,…not Will & Jake (Day 2 Hike)

Working against gravity to gain PE over a shorter distance requires larger force applied in short time intervals

Direct climb up mountain face (no path)

Extremely Difficult

Only highly trained rock climbers(would never even thinking of trying it)

Essentially lifting your entire weight straight up with every step. Requires incredible power, strength and endurance.

The Point…. (cont.)The Point…. (cont.) The steeper the incline plane… the higher

portion of your weight you are going to have to lift with every step.

Low incline, medium incline, direct climb all require the same amount of work because all produce same increase in PE Difference is in how that work is performed.

The steeper the incline plane… the higher portion of your weight you are going to have to lift with every step.

Low incline, medium incline, direct climb all require the same amount of work because all produce same increase in PE Difference is in how that work is performed.

PulleysPulleys Like levers, ramps, and screws…. Sacrifices displacement to achieve a greater force

By pulling a greater displacement you have to apply less force

MA is shown by how many ropes are supporting the load in this case there are two

http://en.wikipedia.org/wiki/Pulley

Like levers, ramps, and screws…. Sacrifices displacement to achieve a greater force

By pulling a greater displacement you have to apply less force

MA is shown by how many ropes are supporting the load in this case there are two

http://en.wikipedia.org/wiki/Pulley

Another PulleyAnother Pulley MA = 4 4 ropes supporting load Force applied is 4 times

less than 100 N So rope must be pulled

with 25 N of force with a distance 4 times greater than the upward distance the load moves

MA = 4 4 ropes supporting load Force applied is 4 times

less than 100 N So rope must be pulled

with 25 N of force with a distance 4 times greater than the upward distance the load moves

LeversLevers

Pull greater distance on long end but achieve greater force over a small distance on the short end

Pull greater distance on long end but achieve greater force over a small distance on the short end