Dopple Effect

Many people should have heard of the ambulance siren but some people may not understand how it works. When an ambulance is approaching toward you, it sounds high pitched and gradually reduced in pitch as it drives away from you. This is due to Doppler effects.

When the ambulance is driving toward you, the air in front of the vehicle is compressed. Thus, reducing the distance between the particles. This situation reduces the length of particles collision. As a result, the time taken to collide from one atom to another atom reduces. This is why the ambulance produces high pitch when it is approaching you.

When an ambulance drives away from you, the opposite explanation applies. The sound frequency is higher when the ambulance is approaching toward you than at idle state. This difference in pitch can tell the driver nearby to give way to the ambulance during an emergency situation.

Doppler effects can also occur in light. This is how scientist used to locate the stars. If the star is moving away from the earth, it will be red in colour because red colour have a longer wavelength. If the star is approaching toward the earth, it will be blue in colour due to higher frequency. This theory is similar to sound. This is the reason why the galaxy is rainbow in colour and we can even trace if the objects in the galaxy is moving clockwise or anti-clockwise around the galaxy core.