## Archimedes' Principle

When a stone is immersed in a bucket completely filled with water, some amount of water spill out of the bucket. The weight of water displaced (spilled) from the bucket can be explained by Archimedes principle.

**Bragg's law** was first proposed by Sir William Bragg and his son Sir Lawrence Bragg. They studied about the diffraction of X-rays and devised a method for determining the wavelength of X-rays.

Michelsons's Method is a precise method for measuring the speed of light. An octagonal mirror *M _{1}* is mounted on the shaft of a variable speed motor. Light from a bright source

According to Newton, when sound waves propagate in air, compression and rarefaction are formed. He assumed that the process is very slow and the heat produced during compression is given to surrounding and heat loss during compression is gained from surrounding. So the temperature remains constant and sound waves propagate through an isothermal process.

Radius of gyration is defined as the distance from the axis of rotation to a point where the total mass of the body is supposed to be concentrated, so that the moment of inertia about the axis may remain the same. Simply, gyration is the distribution of the components of an object. It is denoted by **K**.

The moment of linear momentum of an object is called angular momentum. Angular momentum is represented by **L**.

The angular momentum of an object about an axis of rotation is measured by the product of the linear momentum of the object and the perpendicular distance between the object and the axis of rotation.

The center of mass (not to be confused with center to gravity) of a body is the point which behaves as if all the mass of the body is concentrated there. Thus, if a force acts at this point, the body will accelerate but will not rotate.

The center of gravity (not to be confused with center of mass) of a body is a point where the weight of the body acts and total gravitational torque on the body is zero.

When an object is thrown vertically upwards, it reaches a certain height and comes back to the earth. But when it is given greater initial velocity, it reaches greater height before coming back.

Measurement is a process of detecting an unknown physical quantity by using standard quantity. **For example**: Take a book and use ruler (scale) to find its length. Suppose the length was 20 cm. You underwent through a process called **Measurement **where: