1. III.) Doppler Effect: an observed change in the frequency of a wave when the source or observer is moving
A) Pitch of a sound (how high or low it is) is determined by the frequency at which the sound waves strike the eardrum
1) When an object that is emitting sound waves (i.e. ambulance) is at rest, the sound waves spread out in circles and anyone who is standing near the object will hear the same pitch

2. 2) When an object that is emitting sound waves (i. e
2) When an object that is emitting sound waves (i.e. ambulance) is moving however, the waves are closer together in the direction of the motion. So if one person is standing in the same direction as the motion, the pitch will seem higher than if a person was standing in the opposite direction

3. Doppler Effect-Light
Light from moving objects will appear to have different wavelengths depending on the relative motion of the source and the observer.
When an object in space moves toward us it light waves are compressed into higher frequencies or shorter wavelengths- a blue shift
When an object moves away from us, its light waves are stretched into lower frequencies or longer wavelengths- a red shift.

5. Doppler Effect and the Electromagnetic Spectrum
we can observe light in many other parts of the electromagnetic spectrum such as radio, infrared, ultraviolet, X-rays and gamma rays.
However, the terms redshift and blueshift are still used to describe a Doppler shift in any part of the spectrum.
For example, if radio waves are shifted into the ultraviolet part of the spectrum, we still say that the light is redshifted - shifted toward lower frequencies.

6. The light from most objects in the Universe is redshifted as seen from the Earth.
This is because our Universe is expanding
The redshift of an object can be measured by examining the absorption or emission lines in its spectrum.
When an object in space moves toward or away from us, the absorption or emission lines will be found at different wavelengths than where they would be if the object was not moving (relative to us).