9th Class Physics Notes “Rounding Off & Physical Balance.”

Rounding off:

In dropping the non-significant digits the following rule are followed.

1) Last digit less than 5:

If a digit in a figure is less than 5, then it is ignored.

Example:

3.83 is rounded to 93.8.

2) Last digit greater than 5:

If dropping digit in a figure is greater than 5, then the last retained digit increase by 1.

Example:

9.68 is rounded to 9.7.

3) Last digit equal to 5:

If the last dropping digit is equal to 5 then there are two possibilities;

a) Before ‘5’ even digit:

When the dropping digit is ‘5’ and the last retained digit is even, then the last digit i.e. ‘5’ will be dropped without affecting the next one.  

Example:

67.65 is rounded to 67.6.

b) Before 5 odd digit:

If the dropping digit is ‘5’ and the 2nd last digit is an odd digit then the 2nd last digit is increased by 1 in order to round off 5.

Example:

64.35 are rounded to 64.4.

Q: Physical Balance.

Definition:

It is an instrument which help in measuring unknowns mass of a body by comparing it with standard mass is called physical balance.

Principle:

A physical balance work on the principle of movement (Torque).

Construction:

Physical balance consist of a light and rigid beam of brass, a metallic pillar, a wooden base. Two pans, a metallic printer and a scale. The device is enclosed in a glass box, the whole box has leveling screws, at the bottom to set it horizontal.

Working:

Physical balance is a common balance which has two pan of equal mass which is balanced by a beam. The standard known mass is added to the right side of the physical balance, and the unknown mass is added to the left side of the physical balance. The when both the pan balance each other, then the unknown mass of the object is equal to the standard mass. The total known mass in the left pan is calculated, which gives the mass of the object.