Motion and Measurement of Distances

IMPORTANT TERMS

Motion: - The change of position of a body with time, with respect to a stationary body.

Unit: - A unit is a fixed quantity or a standard of measurement with respect to which a physical quantity is measured.

Length: - The distance of something from one end to the other is known as length.

Odometer: - An odometer is a device that is used for measuring the distance travelled by an automobile.

              

MEASUREMENT

Measurement is the process of finding the length, breadth, size or quantity of a substance. It means the comparison of an unknown quantity with some known quantity. Every measurement involves a number and a unit.

Ancient Methods of Measurement

In ancient times, people used to measure length with the help of different body parts.

• Hand span is the distance between the tip of the thumb and the tip of the little finger of a fully stretched palm.
• Cubit is the distance between the tip of the middle finger and the elbow.
• Fathom is the length of the outstretched arms.
• Foot is the measure of the distance between the end point of the heel and the big toe.

 

Standard units of Measurement

A unit is a fixed quantity or a standard of measurement with respect to which a physical quantity is measured. The metric system is a standard set of units. It was created by the French in 1790.

Scientists all over the world have adopted a common set of units. It is called the International System of Units, also known as SI units. Standard units have a fixed quantity and do not vary from person to person or place to place. Some common standard units of length are centimeter, millimeter and kilometer.

 

Measure	SI Units
Length	Metre (m)
Mass	Kilogram (kg)
Time	Second (s)
Temperature	Kelvin (K)

 

MEASUREMENT OF LENGTH

The distance of an object from one end to the other is known as length. It can be measured using a metre rod, ruler or a measuring tape. The following precautions should be taken while measuring the length using a ruler:

• One should make sure that the edges of the ruler are not worn out. If the edge of the ruler is worn out or broken, the measurement will not be accurate.
• Correct position of the eye is very important for taking measurement. Eyes should be exactly above the point where the measurement is to be taken. If the position of the eyes is not correct, one might get wrong readings.
• Scale should be placed in contact with the object along its length.

 

MOTION  

Motion is the change of position of a body with time, with respect to a stationary body. When a body remains in same position for a long time, it is said to be at rest. An object can have more than one kind of motion.

 

TYPES OF MOTION

There are different types of motion:

Translational Motion

If a body moves as a whole, in a way that all parts of the body move the same distance in a given time is called translational motion. It can be of two types: Rectilinear and curvilinear.

 

Rectilinear Motion

When an object moves in a straight line, it is said to be in rectilinear motion. E.g. A car moving along a straight road, a ball rolling on the ground, a train moving on a straight track, a fruit falling down from a tree are the examples of rectilinear motion.

 

Curvilinear Motion

When an object moves along a curved path, it is said to be in curvilinear motion. E.g. A car taking a turn, a stone thrown up in the air at an angle, a train moving on a curved railway track are the examples of curvilinear motion.

 

Oscillatory Motion

When a body moves to and fro about a fixed point, it is said to be in oscillatory motion. E.g. The movement of a swing, the pendulum of a clock, the vibration of a stretched wire.

 

Periodic Motion

The motion that repeats itself after equal intervals of time is called periodic motion. E.g. Motion of a pendulum, the hands of a clock, motion of the needle of a sewing machine.

 

Non-periodic Motion

A motion that does not repeat itself at regular intervals of time is called non-periodic motion. E.g. A bird gliding across the sky, children playing in the park, a car moving on a road, occurrence of lightning, a dog running on the road.

Repetitive Motion

If a motion takes place again and again, it is known as repetitive motion. E.g. The oscillations of a pendulum, swinging of arms while walking.

Circular Motion

The motion of a body in a circular path around a fixed point is known as circular motion. E.g. Moving of a bicycle wheel, motion of a wheel of a car, motion of the hands of a clock.

Rotation

If a body turns around without shifting its position from one place to another, the motion is called rotational motion. E.g. Merry-go-round, blades of a windmill, the motion of the Earth around its axis, a moving potter's wheel, a spinning top.

Revolution

If a body as a whole moves around in a circular path, the motion is called revolution. E.g. The motion of the Earth around the Sun.

INTERESTING FACTS

• The heavier an object, the greater its mass is and the less it will be accelerated by a particular force.
• One of the most commonly used units, the yard, was defined in the 1100s by English King Henry I as the distance between the tip of his nose and the thumb of his outstretched arm. 
• At first an inch was the width of a man's thumb. In the 14th century, King Edward II of England ruled that 1 inch equalled 3 grains of barley placed end to end lengthwise.
• The ancient Roman soldiers marched in paces, which were the length of a double step, about 5 feet.
• The Great Wall of China is approximately 6,430 Km long (3,995 miles).
• An astronaut can be up to 2 inches taller returning from space as the cartilage disks in the spine expand in the absence of gravity.
• Microseconds, milliseconds, and nanoseconds are examples of very small units of time.
• The pendulum was discovered by Italian scientist and scholar Galileo Galilei in 1602.