Measurement and motion
Class work
I. Define the following:
1. Physical quantity: Any quantity that can be measured is called physical quantity.
2. Standard Unit: It is a standard measure that remains the same whenever,
wherever and by whomever it is used.
3. Light Year: It is the distance travelled by light in one year.
4.Motion: Motion is the change of position of a body over a period of time, with
respect to a stationary object.
5.Translatory Motion: If an object moves as a whole so that every part of the object
moves through the same distance in a given period of time.
6.Parallax Error: An error can occur due to wrong position of the eye while taking a
reading.
II. Answer the following:
1.Name the two inventions that brought about revolution in the field of transport.
Ans: First the invention of a wheel brought a revolution in transport. The second
revolution in the field of transport occurred with the invention of steam engine.
2. What are the two types of error?
Ans: The 2 types of error are; a) Parallax Error b) Instrumental Error
3. Mentions the conditions required to make accurate measurements?
Ans: To make accurate measurements there are following two main requirements:
(i) One must have an appropriate instrument.
(ii) One should know how to use the instrument properly.
4. While measuring the length of a metallic rod the reading of the scale at one end is
8.0 cm and at the other end is 33.7 cm. What is the length of the rod?
Ans:
Initial reading of metallic rod = 8.0 cm
Final reading of metallic rod = 33.7 cm
Length of the rod = Final reading – Initial reading
= 33.7 – 8.0 = 25.7 cm
5. If you are sitting in a moving car, are you at rest or in motion?
Ans: You are at rest because you are not moving with respect to the car.
6. Classify the following as rectilinear, circular, periodic or rotational motion.
a) The motion of plucked string of a Guitar – Periodic
b) The motion of the earth around the sun – Circular
c) The motion of a cyclist on a straight, plane road – Rectilinear
d) The spinning of the earth on its axis – Rotational
7. Explain why hand span cannot be used as a standard unit to measure length.
Ans: If two people take the same measurement, the value obtained by using a ruler
will be similar, but the value obtained using hand span will differ. This is because the
length of the hand differs from person to person.
8. Distinguish between the following.
a) Rectilinear motion and Circular motion
b) Rotational motion and Periodic motion
c) Rest and Motion
S.No Rectilinear Motion
a)
Movement along a straight line from
one position to another.
b)
For example, a bus moving on a
straight highway.
S.No Rotational Motion
a)
Movement in a circular path in
relation to its own fixed axis.
b)
For example, blades of a moving
fan.
S.No Rest
a)
The state in which an object does
not change its position with time
and with respect to its
surroundings
b)
For example, book placed on table.
Circular Motion
Movement in a circular manner in
relation to its own axis or around a
fixed point.
For example, a spinning top.
Periodic Motion
Oscillatory movement along the same
path again and again with same
speed.
For example, pendulum of a clock
Motion
The state in which an object keeps on
changing with time and with respect
to its surroundings.
For example, butterfly flying in
garden.
9. A turning screw undergoes 2 kinds of motion at the same time. Identify the 2 kinds
of motion.
Ans: a) Translatory motion: As a screw is turned, it moves horizontally forward.
b) Rotational motion: In order to move the screw forward, the screw has to be
rotated.
10. Write the similarities and differences between the motion of a bicycle and a
ceiling fan that has been switched on.
Ans:
(i) Similarity: Both the wheel of a bicycle and a ceiling fan exhibit motion on a fixed
axis.
(ii) Dissimilarity: Bicycle moves forward thus executes rectilinear motion but fan does
not show such motion.