Student: Who is Edwin?
Tutor : Hmm.. Good question.. He will probably post the answer here when he finds out.
Student:: I often get confused between the terms centrifugal force and centripetal force could you please enlighten me?
Both terms describe forces associated with circular motion, but let's start with a straight line analogy. If you are in a car whose speed is increasing, the car is being accelerated by a force applied in the direction of travel. Inside the car, you feel as though a force is pushing you back in your seat toward the rear of the car. Those two forces, one forward and one backward, are the straight line equivalents of centripetal and centrifugal force in circular motion.
If the car described above is moving at a constant speed, but changing direction as it travels around a curve, it ALSO is accelerating. Acceleration occurs anytime VELOCITY changes, and velocity is defined as a combination of speed AND direction. The car is changing direction because of a force (supplied by friction between road and tires) directed toward the center of the curve. That is the centripetal force, which is always directed toward the center of the curve. When you swing a weight around your head at the end of a string, your hand supplies the centripetal force to keep the weight moving in a circle.
Back inside the car, you feel a force pushing you AWAY from the center of the curve. That force is called centrifugal force, which is always equal in magnitude but opposite in direction from centripetal force.
You have a lot of company in your confusion. A lot of people get centrifugal and centripetal force mixed up. I did too! Here is the way I keep them straight. ' Centripetal ' comes from the Latin word for ' center seeking ' so the direction that centripetal force acts in is towards the center of a circle. Think of the 'p' as the first letter of 'pushed', as in 'being pushed towards the center'.
'Centrifugal' has two Latin roots in it. You can see the same 'cnetri' from centripetal, so the idea of 'center' is a part of this word. The other Latin root is 'fugere', which means 'to flee'. So, ' centrifugal ' means ' to flee from the center '. Think of the 'f' as the first letter of flee as in 'fleeing from the center of the circle'.
I presume you know that of these two, only centripetal is the real force . For something to go in a circle it must be being pushed or pulled (there's the 'p' again!) towards a center point; otherwise it would be going in a straight line. Centrifugal 'force' is really a function of the inertia of the object being pushed into a circle. It is not really a force at all, it is simply the tendency of an object to go in a straight line.
Student: So, in reality, do standing/stationary waves flip about horizontal the axis like a skipping rope?
Tutor : No, the particles vibrate in a direction perpendicular to the horizontal axis very much like in progressive waves.
Student: Is there a difference between diffraction and diffraction gratings?
Tutor: This question is like asking is there a difference between wash and washing machine? Or run and running shoes?
Diffraction refers to the Process/Phenomenon whereby waves are bend round obstacles.
Diffraction grating is a Device that has many slits on it.
So, ya I hope you can see the difference now.
Student: How do diffraction gratings tell us information about distant stars and galaxies?
Tutor: Wow.. I am impressed such a "cheem" question can be a frequently asked question... Anyway here's the answer..
The connection between diffraction gratings and stars is found in spectroscopy, which is the study of the relative brightness of an object at each wavelength of light (electromagnetic radiation) it emits or absorbs. Each element has a unique 'fingerprint' determined by the allowable electron energies surrounding its nucleus, causing it to emit or absorb specific wavelengths of light.
Information about a star's composition, magnetic fields, motion, temperature and pressure can, therefore, be obtained by analyzing its light's intensity at each wavelength. To allow that analysis, the star's total emitted light must be broken down into individual wavelengths just at a prism or rainbow separates sunlight into distinct wavelengths, or colors.
A prism takes advantage of dispersion, which results from the fact that different colors of light travel through glass at different speeds, depending on wavelength.
A diffraction grating can accomplish the same separation of colors because of diffraction. A light ray reflected (or transmitted) by a grooves in the grating will either interfere constructively or destructively with the ray from the groove next to it, depending on the angle it emerges and the light's wavelength. You can see this color separation by looking at white light reflected from the grooves of a CD.
The advantage of a grating over a prism is that light passing through a prism can be absorbed (and lost), while a grating's reflected light spectrum does not have to be transmitted through any material. It is the same advantage of using a reflecting telescope over a refracting one.