# WAVES.

## Presentation on theme: "WAVES."— Presentation transcript:

WAVES

WARM UP! What do you think of when you hear the word wave? Write a brief description of what you think a wave is. Then, write a short paragraph describing a time you might have experienced waves.

START UP ACTIVITY TURN TO PAGE 573
COMPLETE THE ACTIVITY ON ENERGETIC WAVES ON THE BACK OF YOUR WARM-UP ANSWER ANALYSIS QUESTIONS 1-3 IN COMPLETE SENTENCES THIS WILL BE COLLECTED!

REVIEW-What are the 7 forms of energy?
1. Mechanical (potential and kinetic) 2. Electromagnetic (light) 3. Chemical (stored in bonds-fuel, food, batteries) 4. Electrical (movement of electrons) 5. Thermal (heat) 6. Nuclear (fission and fusion) 7. Sound

WHAT IS A WAVE? A TRANSFER OF ENERGY through matter OR empty space
A MEDIUM is any material that a wave travels through. A medium can be a solid, liquid or gas.

NATURE OF WAVES As a wave travels, it does work on everything in its path. The waves in a pond do work on the water when it makes the water move up and down. The waves also do work on anything floating on the water’s surface.

Can anyone describe the energy transfers that are occurring here?
Moving Object Waves show transfer of energy from propeller through water Medium=Water

NATURE OF WAVES Waves travel through a medium, but they do not carry the medium with them.

Waves travel through a medium!

THERE ARE 2 MAJOR CATEGORIES OF WAVES
MECHANICAL ELECTROMAGNETIC

MECHANICAL WAVES Need a medium to transfer energy! CANNOT travel through empty space OCEAN WAVES AND SOUND WAVES ARE EXAMPLES

Electromagnetic Waves?
Do not need a medium, CAN travel through empty space! Electromagnetic waves (light waves, microwaves, x-rays) can travel through empty space

NATURE OF WAVES We now know that waves can be mechanical or electromagnetic, but there are also 3 types of waves: Three types of waves: TRANSVERSE LONGITUDINAL SURFACE/WATER

TRANSVERSE WAVES Transverse waves move perpendicularly to the direction the wave is moving Transverse waves are made up of CRESTS and TROUGHS electromagnetic waves are examples of transverse waves.

TRANSVERSE WAVE!

TRANSVERSE WAVE!

Time to Practice Use your Slinky or rope to demonstrate a transverse wave: Work with a partner One of you move your end of the Slinky back and forth (left and right, like a snake crawling), perpendicular to its stretched length. The other student must hold his or her end of the Slinky still A series of transverse waves will be generated and will travel through a medium (Slinky)

LONGITUDINAL WAVES Particles move parallel to the direction of the wave When the particles move close together it is called COMPRESSION and when they move farther apart RAREFRACTION.

LONGITGUDINAL WAVE vs. TRANSVERSE WAVES!

Vibrates parallel to (in the same direction of) wave travel
sound waves

LONGITUDINAL WAVES!

LONGITUDINAL WAVES Sound Waves are longitudinal waves. Sound waves travel by compressions and rarefactions of air particles.

Work with a partner Stretch it out along the table One of you grasp and draw several coils of a stretched Slinky toward yourself Release the coils The other student must hold his or her end of the Slinky still A longitudinal wave pulse will be generated and travel down the length of the Slinky.

SURFACE/WATER WAVES Surface waves look like transverse waves, but the particles of the medium move in circles rather than up and down.

A combination of longitudinal & transverse

What do you remember from last class? No notes allowed!
Using a Venn diagram, compare and contrast mechanical and electromagnetic waves! Draw and label the parts of a transverse and longitudinal wave. Give one example of a type of energy that moves using a transverse wave, and one example of energy that moves using a longitudinal wave

Let’s make a model! Fold your piece of paper in half hotdog style!
2) On the top half, use some yarn to make a transverse wave. Neatly label the crest and the trough! 3) On the bottom half, make a longitudinal wave. Neatly label the compression and the rarefactions Now…put it aside…we will add more later!

PROPERTIES OF WAVES

THERE ARE 4 BASIC PROPERTIES OF WAVES!
1) AMPLITUDE 2) WAVELENGTH 3) FREQUENCY 4) SPEED

WHAT IS AMPLITUDE? AMPLITUDE IS THE GREATEST DISTANCE A WAVE MOVES AWAY FROM THE REST POSITION. LARGER AMPLITUDE = MORE ENERGY!

AMPLITUDE IN TRANSVERSE WAVES!

MEASURE OF HOW TIGHT THE COMPRESSIONS BECOME OR HOW LOOSE THE RAREFACTIONS.

WAVELENGTH The distance between any 2 corresponding points on a wave.
For example, the distance between 2 crests in a transversal wave or 2 compressions in a longitudinal wave

WAVELENGTH AND ENERGY SHORTER WAVELENGTH = MORE ENERGY
HOW DOES SHAKING A ROPE OR A SLINKY AT DIFFERENT RATES AFFECT THE WAVELENGTH OF THE WAVE THAT MOVES THROUGH THE ROPE/SLINKY? WRITE A HYPOTHESIS?

CHANGES IN WAVLENGTH!

How can you measure wavelength in longitudinal waves?

FREQUENCY The number of waves that pass a certain point in a given amount of time Measured in HERTZ (HZ) If 1 wave passes in 1 second the frequency is 1 Hz! HIGHER FREQUENCY = MORE ENERGY

Let’s review!

WAVE SPEED! Speed, wavelength, and frequency are related!
Different waves travel at different speeds. Speed = wavelength x frequency

WARM UP: continued! Draw a transverse wave with a small amplitude!
Draw a transverse wave with a large amplitude How can I measure amplitude in a longitudinal wave? Draw a transverse wave with a small wavelength. Draw a transverse wave with a large wavelength. How can I measure wavelength in a longitudinal wave? Draw a transverse wave with a high frequency What 2 properties of wave affect wave speed?

How do waves interact with objects? How do waves behave when they move between different mediums (media)? How do waves interact with other waves?

HOW DO WAVES INTERACT WITH OBJECTS?
QUESTION 1 HOW DO WAVES INTERACT WITH OBJECTS?

1. REFLECTION When a wave hits an object through which it cannot pass, it bounces back. This is called REFLECTION. All waves can be reflected.

Examples When light waves are reflected off an object, that means you can see that object. For example, light waves reflecting off the moon allow you to see the moon. When sound waves reflect it is called an echo!

Reflection When a wave reflects, the angle of incidence is equal to the angle of reflection See for yourself.

2. Absorption and 3. Transmission
Waves that are not reflected are either absorbed OR They are transmitted (pass through the substance) like light through a glass window or a pair of glasses

4. DIFFRACTION Diffraction is the bending of waves around a barrier or through a opening. The amount of diffraction of a wave depends on its wavelength and the size of the opening or barrier

DIFFRACTION If the barrier or opening is larger than the wavelength of the wave, there is only small diffraction If the barrier is smaller, the diffraction is larger

WATER WAVE DIFFRACTION

DOUBLE SLIT DIFFRACTION

LIGHT DIFFRACTION A very simple demonstration of diffraction can be conducted by holding your hand in front of a light source and slowly closing two fingers while observing the light transmitted between them. As the fingers approach each other and come very close together, you begin to see a series of dark lines parallel to the fingers. The parallel lines are actually diffraction patterns. This phenomenon can also occur when light is "bent" around particles that are on the same order of magnitude as the wavelength of the light. A good example of this is the diffraction of sunlight by clouds that we often refer to as a silver lining, illustrated in Figure 1 with a beautiful sunset over the ocean.

DIFFRACTION OF LIGHT THROUGH CLOUDS

If you can hear it, why can’t you see it?
The amount of diffraction depends on the wavelength and the size of the barrier. You can hear music around the corner of a building because sound has long wavelengths and are able to diffract around corners. You can’t see who or what is making the music because light waves are much shorter than sound waves so light is not diffracted as much.

QUESTION 2 HOW DO WAVES BEHAVE WHEN THEY MOVE BETWEEN MEDIUMS?

1. REFRACTION REFRACTION is the bending of waves when waves move from one medium to another. When a wave hits a new medium, it changes speed and the wavelength changes!

RAINBOWS ARE REFRACTED LIGHT
When light waves from the sun pass through a droplet of water in the air, the light is refracted. The different colors of light travel at different speeds through the drop therefore the colors are refracted by different amounts= RAINBOW

Question 3 HOW DO WAVES INTERACT WITH EACH OTHER?

INTERFERENCE You already know that all matter has volume so 2 things cannot be in the same place at the same time. BUT WAVES ARE NOT MATTER…THEY ARE ENERGY SO 2 WAVES CAN BE IN THE SAME PLACE AT THE SAME TIME.

INTERFERENCE TWO WAVES CAN MEET, SHARE THE SAME SPACE AND PASS THROUGH EACH OTHER. WHEN 2 OR MORE WAVES OVERLAP, IT IS CALLED INTERFERENCE. THERE ARE TWO TYPES OF INTERFERENCE

CONSTRUCTIVE INTEREFERENCE
HAPPENS WHEN THE CRESTS OR TROUGHS OVERLAP TO COMBINE THEIR ENERGY TO MAKE HIGHER CRESTS OR DEEPER TROUGHS

DESTRUCTIVE INTERFERENCE
Destructive interference happens when the crest of one wave and the trough of another cancel each other.

VIDEO

STANDING WAVES A wave that looks as though it is standing still, but it happens as a result of interference between waves and reflected waves.