# A question in physics

scottbekerham
I have no idea about physics and i do not even remember anything about high school physics . I'm a medical student but i have a question in physics . this question may sound strange or stupid but if anyone can answer me , it wold be appreciated .
if a particle moves at a specified velocity as a part of radiation . can this particle lose kinetic energy gradually so as to reach a much lower velocity at a specified calculated point ?
is there a relationship between the velocity or energy of that particle and penetrance of materials?
can we make a molecule (any molecule ) to move at a specified velocity and then gradually lose energy?
i want the answer to these question as I'm doing a research for the college

Homework Helper
if a particle moves at a specified velocity as a part of radiation . can this particle lose kinetic energy gradually so as to reach a much lower velocity at a specified calculated point ?
If it is a particle with mass, such as an electron or proton then yes.
It needs some external force to slow it down, such as a magnetic field. Electrons losing energy in a magnetic field are used to generate X-rays for example.
A masslass particle such as light can't have any speed other than 'c' (in vacuum)

is there a relationship between the velocity or energy of that particle and penetrance of materials?
Partly, it also depends on the method of absorbtion.
Light is absorbed by bonds in the material which have the correct energy to match that of the photon, so particlular wavelengths can be effectively blocked while others pass through.
Different mechanisms apply to just bulk absorbtion of things like xrays.

can we make a molecule (any molecule ) to move at a specified velocity and then gradually lose energy?
If you apply a force, yes. So if the moelcule is charged you can slow it down with an electric field. A mass spectrometer puts the same charge on molecules of different mass, an electric field then slows them with the same force - since heavier molecules will slow less (imagine putting the same braking force on a car and truck) you can measure the masses of the molecules and identify them.

Rajini
Hi mgbphys,
i think he need some information on attenuation of x-rays [medical physics]..if this is what you need please reply..i can give you some relevant information.

Mentor
if a particle moves at a specified velocity as a part of radiation . can this particle lose kinetic energy gradually so as to reach a much lower velocity at a specified calculated point ?
Essentially,yes. That is the basis of proton beam therapy: http://en.wikipedia.org/wiki/Proton_therapy