Warm-up:Write this in your notes.

1. What is the original source of energy that powers wind turbines?

2. What time of day do you feel sea breezes? Explain why using the following terms: temperature, density, pressure and wind.

Nuclear fusion from the Sun

During the day, because the air above land heats up at a faster rate, which is less dense and rises, creating a lower pressure than that over the ocean. Since wind blows from an area of higher pressure (over the ocean) towards an area of lower pressure (over the land), this creates a sea breeze. Now explain what happens at night.

Agenda 10/26/09• Homework Check and review• Review the quiz• Go over lab last week (wind speed)• Notes: Power & Energy• Solve Power Problems

Homework:• Finish problems & lab if not done

in class.Learning Goal: use formulas to calculate power

Source: http://apollo.lsc.vsc.edu/classes/met130/notes/chapter10/graphics/global_precip.jpg

Coriolis Effecthttp://www.youtube.com/watch?v=mcPs_OdQOYU&feature=player_embedded

• The apparent deflection of objects (such as airplanes & wind) moving in a straight path relative to the earth's surface.

• From the Earth's surface an object in the air appears to curve off of its course.

• It’s not actually moving off of its course but it

appears to be happening because the Earth’s surface is rotating beneath the object.

Myth of the Coriolis Effect

• One of the biggest misconceptions is that it causes the rotation of water down the drain of a sink or toilet.

• This is not the cause of the water's movement. The water is simply moving too fast down the drain to allow for the Coriolis to have any significant impact.

Review the Quiz

B

A C

Review of Energy:

• Energy in general is defined as the ability to cause a change in self or surroundings.

• Different types of energy:light (radiant), heat (thermal), electrical, chemical, nuclear, mechanical, kinetic and potential.

• But the types we’re interested in now are the types that have to do with motion problems.

• The standard scientific unit for all types of energy is the Joule.

1 J = 1 N m = 1 kg m∙ ∙ 2/s2

–This is the same unit used for work.

Standard Unit of Measure:

The Physics of Work:

Definition of Work:

• The product of force and distance.

• we sometimes think of work as a transfer of energy by mechanical means.

How is Work related to Energy?

Power Power is the rate at which energy is transformed from one form to another.

Unit: Watts (W)1W = 1 Joule/second

P = Et

Power Energy

Time

Finish the Lab

• Complete questions 6 & 7 now at your desk using the map I will put up shortly.

• Complete the calculations and the rest of the analysis questions at home.

• Map

ConceptQuestions

1. Which light bulb is more powerful, one that can transform 100 Joules per second, or one that transform 60 Joules per second?

2. Which motor is more powerful, one that can lift a certain weight 1 meter in 2 seconds, or one that can lift the same weight 1 meter in 5 seconds?

Example Problems

1. What is the power rating of a heater that can transform 5000J of energy

from electric to heat every 12 seconds? 2. What is the power rating of a motor that

transforms 2400J of energy from electric to kinetic in 5 minutes?

3. How much energy is transformed by a 75W light bulb in 23 seconds?

4. How much energy is transformed by a 500W device in 8 minutes?

More Practice1. What is the power rating of a motor if it is able to

transform 5000J of energy from electric to kinetic in 30 seconds?

2. A certain light bulb is able to transform 1200 Joules of energy every 20 seconds. What is the power rating of this bulb?

3. How much energy (in Joules) is transformed from electric to heat by a 1500W toaster-oven during a 45 second toasting?

4. A 250W television is accidentally left on for 3 straight days. How many Joules of energy does the TV ‘use’?