What are mechanical waves? What do you think waves carry? Can you see waves? Examples?

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# What are mechanical waves? What do you think waves carry? Can you see waves? Examples? - PowerPoint PPT Presentation

What are mechanical waves? What do you think waves carry? Can you see waves? Examples?. Mechanical Waves. Mechanical waves are disturbances in matter that carry energy from one place to another. Usually require matter through which to travel

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Presentation Transcript
What are mechanical waves?

What do you think waves carry?

Can you see waves? Examples?

Mechanical Waves
• Mechanical wavesare disturbances in matter that carry energy from one place to another.
• Usually require matter through which to travel
• The matter a wave travels through is called a medium.
• Medium can be a solid, liquid, or gas
• Some waves can travel through space…with no medium!
What happens when…
• A wave meets a hard surface like a wall?
• Reflection
• A wave enters a new medium?
• Refraction
• A wave moves around an obstacle?
• Diffraction
Axis

An imaginary line which runs through both

poles of a planet.

Rotation of the Earth
• The Earth is spinning upon a central axis.
• The Earth's axis is tipped over about 23.5° from the vertical.
• The Earth rotates around once in 24 hours.
Rotation of the Earth

http://www.classzone.com/books/earth_science/terc/content/visualizations/es0404/es0404page01.cfm?chapter_no=visualization

Revolution of the Earth
• The earth revolves around the sun.
• The orbit is elliptic.
• The Earth's tilt stays constant.
• The Earth completes one revolution in 365 days.

ECLIPSES

• A solar eclipse is when an object in space casts a shadow from the sun on another object in space.
• A lunar eclipse occurs when the Earth blocks the sunlight from reaching the moon.

Question: Why do lunar eclipses occur only during full moons?

Answer: That is the only time that the earth comes between the moon and sun.

Question: Why don’t we have a lunar eclipse every full moon?

Answer: The tilt of the moon’s orbit is 5° different than the earth

Answer: The light from the sun gets bent as it passes through our atmosphere causing it to appear red.

Question: Why does the full moon appear to be red during certain times of the year?

Magnetic Fields

The region where the magnetic forces

act is called the “magnetic field”

Charges
• Matter is made of atoms
• Atoms are made of sub-atomic particles
• Protons are positively charged
• Electrons are negatively charged
• Atoms are electrically neutral
• This means positive charges equal negative charges
Charging the Atoms

Electrons are loosely held by atoms of some materials

These electrons can be moved

Loosing these electrons makes the atoms electrically charged

Friction, conduction, and induction are three ways atoms can be charged

Static Electricity
• Static electricity is the build up of electric charges on an object
• Electrons move off an object to another causes the ELECTRIC DISCHARGE
• Lightening is a wonderful and exciting example of this phenomena
Current Electricity
• Some materials allow the charges to move freely through them
• These materials are called conductors
• Some examples of conductors are copper, iron, aluminum, and zinc
Insulators
• These materials do not allow the charges to move freely through them
• These materials are called the insulators
• Some examples of insulators are rubber, plastic, and wood

1. There are North Poles and South Poles.

2. Like poles repel, unlike poles attract.

3. Magnetic forces attract only magnetic materials.

4. Magnetic forces act at a distance.

5. While magnetized, temporary magnets act like permanent magnets.

Some More Facts

9. A charged particle experiences no magnetic force when moving parallel to a magnetic field, but when it is moving perpendicular to the field it experiences a force perpendicular to both the field and the direction of motion.

10. A current-carrying wire in a perpendicular magnetic field experiences a force in a direction perpendicular to both the wire and the field.

Series and parallel circuits

Series Circuit

Parallel circuit

There is so much air above you that at sea level you have 14.7 lbs/in2 pushing on you.

Gravity causes most of the air to be pulled down to the surface.

Air Pressure
As the air pressure decreases, the density of the air decreases. The air particles are not squashed together as tightly the higher one goes. This is caused by gravity!

The air at sea level and at 6km has the same 21% oxygen, but at 6km there are fewer molecules, so you take in less oxygen with each breath.

Shows density of air

Altitude and Density
Troposphere: temperature at surface is warmed by the earth absorbing energy from the sun.

Air cools as it rises (air molecules lose energy)

The air cools by about 6.5°C for every 1-km above the ground.

In 10 KM air will cool

6.5*10=65

Temperature and the Troposphere

Without greenhouse gases, energy pretty much passes straight through!

Temperature and the Mesosphere
Solar radiation first hits this layer, so the few particles that are here can gain lots of energy. They move rapidly, so they have a very high temperature.

But the air is so thin here that it takes special instruments to measure the temperature accurately.

So even though it is very hot (over 1000°C), it would feel cold because there are so few particles to transfer heat to you.

Temperature and the Thermosphere
The Troposphere
• Lowest (inner) layer
• weather occurs here
• we live in it.
• “tropo” means turning or changing conditions
• depth varies from 9km above the poles to 16km at the equator
• shallowest (least thick) layer, but contains most of the mass (90%).
The Stratosphere
• “strato” means layer or spreading out
• Contains the ozone layer which absorbs energy and causes the temperature to rise
• The ozone layer protects the surface from dangerous UV rays
Drop in temperature marks beginning of mesosphere

“Meso” means middle

Most meteors burn up here

The Mesosphere
The Thermosphere
• Very top layer
• Air is very, very thin, about 1/1000th as dense as the air at sea level
• “Thermo” means heat
• Extends from 80km to space
• No definite outer edge
• Very hot (over 1000°C), but since air is so thin it would not feel warm at all.
• Divided into two parts, the ionosphere and the exosphere
The Ionosphere
• Energy from sun strips the electrons from the gas molecules creating charged particles called ions.
• Radio waves can bounce off of ions, allowing radio waves to travel great distances.
• The aurora borealis (Northern Lights) occur here
The Exosphere
• “Exo” means outer
• Extends for 1000’s of miles
• Satellites orbit here
• No definite edge
• Molecules gradually escape out into space