Waves

Bellwork 4/10/13 Complete the following questions in your TCAP practice book: 1, 4, 9, 12, 17, 20, 28, 33

What is a Wave? A Wave is a disturbance that transfers energy from place to place. In order to pass its energy along, waves can pass through a medium.(-- the material through which a wave travels). (A medium can be a gas, liquid, or solid).

Not all waves pass through a Medium…… Some waves DO NOT need a medium in order to pass its energy along. For example, electromagnetic waves can go through matter such as air, water, and glass but they DON’T have to have a medium to pass their energy along. (Other examples include microwaves, x-rays used by doctors and dentists, and even light)

Waves transfer energy, not matter Waves transfer energy, not matter. The water in the waves below are carrying energy but are not moving. Waves can only exist if they have energy to carry.

What causes waves? Waves are created when a source of energy causes a medium to vibrate. A vibration is a repeated back and forth or up and down motion.

How do we classify waves? Waves are classified according to how they move. We classify waves based on the direction in which the particles of the medium vibrate compared to the direction in which the wave moves.

Types of Waves: Longitudinal Transverse Surface

Transverse Vibrates perpendicular (at right angles) to the wave travel. These waves move in an “up and down” motion. (Similar to waving a moving rope)

Parts of a transverse wave: The highest point on a transverse wave is called the “crest”. The lowest point on the transverse wave is called the “trough”.

Transverse Use your Slinky to demonstrate a transverse wave: Work with 3 other people (4 in a group total) 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 Vibrates parallel to (in the same direction of) wave travel. It produces a “back and forth” type of motion. (ex: sound waves) It’s similar to pulling one end of a slinky. The wave travels through the medium from one end and back again to the other.

Parts of a Longitudinal wave… The parts of longitudinal waves where the particles are “crowded” is called the compression. The parts of the waves where they are “farthest apart’ is called rarefaction. “Compression” --Rarefaction

Longitudinal Use your Slinky to demonstrate a longitudinal wave: Work with your group again. 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.

Longitudinal Use your Slinky to demonstrate a longitudinal wave: Work with a partner Stretch it out along the table One of you stretch a segment of the Slinky 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 Waves These are a combination of longitudinal & transverse waves. They look like transverse waves, but the particles travel through the medium in circles rather than up and down. The particles also move forward at the crest of each wave and move backwards at the trough.

“Properties of waves” Imagine you are floating on your air mattress in the pool and a friend dives in and creates a huge wave that sends your mattress “a rock-in”!! We can compare the different types of waves similar to the actions that were created by your friend.

Properties of Waves….. Waves have several properties such as: a) Amplitude -------- (the height of the wave) b) Wavelength -------- (the distance between the crests) c) frequency d) wave speed

“Amplitude” The amplitude of a wave is related to its “height”. A wave’s amplitude is the maximum distance that the particles of the medium vibrate from their rest point. The rest point is the point where the particles of the medium stay where there is no disturbance.

“Wavelength” This is the distance between two crests or two troughs. The shorter the wavelength the greater the amount of energy carried. The longer the wavelength the less amount of energy carried.

“Frequency” --is the number of waves produced in a given amount of time. The higher the frequency, the greater the amount of energy that was made. The lower the frequency, the less amount of energy that was made. Low frequency High frequency

“Frequency” is similar to the movements of a jump rope. Moving the rope quickly makes a larger number of waves. (in a given time). Moving the rope slowly makes a lower number of waves.

Simulation on Amplitude and Frequency http://www.classzone.com/books/ml_science_share/vis_sim/wslm05_pg18_graph/wslm05_pg18_graph.html

Brainpop: How stuff works video clip on waves After the videos, complete the worksheet: “Diagram of a Wave”.

TCAP Practice Questions Review…. Complete question #’s: 5, 11, 32, 38, and 44

Wave Speed The speed of any wave can be calculated from this equation. Wave Properties 2 Wave Speed The speed of any wave can be calculated from this equation. In this equation, the wavelength is represented by the symbol, , which is the Greek letter lambda. = wavelength F = frequency V= Wave speed

Sample problems: Wave Speed 2 Sample problems: Wave Speed 1.Determine the wave speed of a wave that has a wavelength of 5 m and a frequency of 4Hz. 2. What is the frequency of a wave if the wave has a speed of 12cm/s and a wavelength of 3 cm? 3. A wave has a frequency of 5 Hz and a wave speed of 18 m/s. What is its wavelength?

TCAP Practice Questions Review…. Now let’s get out your 2013 TCAP practice book and complete the following questions: 19, 23, 49, 53, 63, & 68. Then we will go over them and discuss the answers.