Science Notes - motion

7/31/2019 Science Notes - motion

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SCIENCEMOTION

Body at rest : A body is said to be in the state of rest when it remains in the same position with respect to

time.

e.g.: The position of trees around the building is not changing with respect to the building. Then the trees

are at rest.

Body in motion : A body is said to be in the state of motion, when it continuously changes its position

with respect to time.

e.g.: When we are cycling or running, we are changing position with respect to trees and buildings. we

are said to be moving

DISTANCE AND DISPLACEMENT

Distance is the length of the path covered by a body. It has no sense of direction so it is a scalar quantity.

Its SI unit of measurement is meter or m

The distance between the two places is not the same; it depends upon the path chosen.

Displacement: The shortest distance, or distance travelled along a straight line, is known as

displacement.

If we draw a semicircle of radius 10cm. Then,

Displacement = r + r = 20cmDistance = 2pr/2 = 10 x 22/7 cm = 31.4cm

UNIFORM MOTION AND NON UNIFORM MOTION

If an object covers equal distances in equal intervals of time, it is said to be in uniform motion.

If an object covers unequal distance in equal intervals of time, it is said to be in non-uniform motion.

MEASURING THE RATE OF MOTION Speed :It is the distance travelled in one second (or) rate of distance travelled.

Q. A car starts from Samastipur and reaches Patna in 6 hour. A bus takes 8 hour to travel the same

distance. Which has moved faster? Why?



The car travels faster than the bus, because it covers the distance in a short time.

When a body covers a distance in a short time, it is said to be fast. If it takes more time to cover the

distance, it is said to be slow.

Hence, Speed is the quantity used to say whether the motion is slow or fast.

Speed = Total Distance travelled/ Time taken

Speed has no sense of the direction of motion so it is a scalar quantity

SI Units: Speed is measured in m/s (or) m/s It can also be expressed in km/hour (or) kmh-1

Velocity : The speed with direction is known as velocity. So to measure the velocity, you should consider

displacement instead of distance. Velocity is the displacement made in one second (or) rate of change of

displacement. Rate of change means, change per second.

Velocity = Displacement/Time

It S. I. Unit is also m/s

Uniform Velocity : Equal displacement covered by a body in equal intervals of time is known as uniform

velocity.

Acceleration is the change in velocity of an object per second or rate of change of velocity.

Acceleration = Change in velocity/Time taken. The unit of acceleration is m/s2 or ms-2

There are two cases of of change of velocity

If the velocity of the body increases with time, the acceleration is positive, and the kind of motion is called

accelerated motion.

If the velocity of the body decreases with time, the acceleration is negative (retardation), and the motion

is called decelerated motion.

Uniform Acceleration: If an object travels in a straight line and its velocity increases or decreases by

equal amount in equal intervals of time, then the acceleration of the object is uniform.

We can derive a formula for acceleration.

a= [v – u] / t

Where u - initial velocity, v - final velocity t – time.





Figure 2 velocity - time graph ––

If the object moves at uniform velocity, the height of its velocity-time graph will not change with time. Itwill be a straight line parallel to the x-axis.

Since the product of velocity and time give displacement of an object moving with uniform velocity. Thearea enclosed by velocity-time graph and time axis will be equal to the magnitude of the displacement.

Note:

In the case of non-uniformly motion, velocity-time graphs can have any shape

If an object moves along a straight line with uniform acceleration, it is possible to relate its velocity,acceleration during motion and the distance covered by it a certain time interval by a set of equationsknown as the equation of motion . These equations are given as

V = u + at .....(1)

S = ut + 1/2at2 ....(2)

2 as = v2 - u2.....(3)

Here u is the initial velocity of the object which moves with uniform acceleration a for time t, v is the finalvelocity, and S is the distance travelled by the object in time t

If an object moves in a circular path with uniform speed, its motion is known as uniform circular motion . If an object takes t second to go one around the ircle path of radius r, the velocity is given as

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Science Notes - motion