Page 128 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

This is the acceleration due to gravity. It is
See how brisk I am
represented by the letter g.

Retardation My name is Cheetah. I can run at a
great speed. Do you know what my
Examine Table 9.10 and find out whether the
speed is? 25 m/s to 30 m/s. My
velocity of the car increases or decreases
speed changes from 0 to 20 m/s in
when it moves from D to E.
2 second. See how good my
What is the rate of change of velocity? acceleration is!
Does the velocity increase or decrease when
the car moves from E to F?

What is the rate of change of velocity?
Didn't you observe that the acceleration is
negative here? This kind of acceleration is known
as retardation or negative acceleration. Its unit is
2
also m/s .
Find out whether the acceleration is positive or
negative in the given situations.

a ball rolling on a level ground.
a train starting from the station.

the motion of a stone thrown up-when it goes up and comes
down.

Aren’t you now familiar with the concepts of speed and
acceleration? The speed of vehicles increases when there is
acceleration. Excessive speed of vehicles may result in accidents.
We can minimise deaths due to accidents to a great extent if we
obey traffic rules and signals put up on the side of the roads.
Observe the sign boards given below.

Speed
thrills Don't mix drink Better late than Wear helmets
but with drive never while driving
kills motor cycles

Are the deaths caused by accidents the result of negligence and
excess speed of vehicles alone? Don’t you think that the
carelessness of pedestrians is also one of the reasons? What
precautions should pedestrians take? Write them down.

Basic Science VIII 127