Wave behaviors: Mechanical vs electromagnetic

• There are longitudinal waves, but we are focusing on transverse waves!

• Doesn't require a medium to travel!

• can only travel through a medium.

• can travel through a solid, liquid or a gas.

• can only transfer energy, not matter​.

• Most common type is a sound wave. ​

What is a mechanical wave?

Matter can Transmit Light

• Light is a type of electromagnetic wave, so it can travel through empty space

• When light meets with a material, it can be passed through the material – we call this transmission

• Transparent – Matter that transmits light; you can see through them

• Translucent – light is scattered in different directions; you can't see all the way through

Matter can Absorb Light

• Opaque – materials do not let any light pass through; they can reflect, absorb, or both

• Absorption – transfer of light energy to matter (think like how a sponge soaks up water)

Matter Can Reflect Light

• Reflection – the bouncing of light off a surface; The Law of Reflection states that a light way striking a mirror will bounce off the mirror at the same angle

• When light bounces off a smooth surface it reflects in a uniform way

• When light bounces off a rough surface it scatters in many different directions

What determines what colors we see?

• Remember the colors we can see are called visible light – Roy G. Biv

• Light can be reflected or absorbed. Objects that appear a specific color are because those are the light waves that are reflected

• Objects that are translucent or transparent can absorb, reflect, and transmit light waves.

Black and White Objects

• When an object absorbs all light waves, it appears black

• When an object reflects all light waves, it appears white

• Any other color that you see is due to reflection of light waves

Light waves change when interacting with matter

Refraction - is the change in direction of a wave as it passes from one medium into another at an angle.

-Examples: shining white light through a prism creates a rainbow

Light waves change when interacting with matter

Diffraction - occurs when a wave bends as it passes through an opening or around an object

Example - sunlight shining around a cloud

Mirrors and Lenses

Concave vs. Convex

Concave is curved inward like a bowl or a spoon

Convex is curved outward like the back of a spoon

Sound Wave Interactions

What affects the speed of sound?

• Two main factors affect the speed

  of sound: the type of medium that the sound travels through, and

  the temperature of the medium.

• Sound travels fastest through solids because solids are denser than liquids or gases

• Sound travels faster through hot air than through cold air.

Matter Can Reflect Sound Waves

• Reflection is the bouncing back of a wave when the wave hits a barrier

• Example - an echo

​Matter Can Absorb Sound Waves​

• A rough wall will absorb sound better than a smooth wall will.

  And soft materials absorb sound better than hard materials do

Diffraction

Diffraction is how a wave changes when it interacts with an obstacle or an opening.​

​If a wave hits an object it cannot pass through, it bends to move around the object.