Page 1 - Lesson notes-Motion and speed

SAI International School
Class VII
Lesson Notes
Subject: Physics
Ch-Time and Motion
Subtopic: Motion and Speed

Motion:

When a body changes its position with respect to its surroundings, it is said to be in motion.

Slow motion:
When a body takes more time to cover a certain distance as compared to another body then it
is said to be in slow motion.
Fast motion:
When a body takes less time to cover a certain distance as compared to another body then it
is said to be in fast motion.
Speed:

It is defined as the distance covered by a body per unit time.

&"'!"# %$
'($$& =
!"#$

SI unit of speed is m/s.

Other units: Km/h (kilometer per hour), miles/h (miles per hour)

To convert m/s into km/h, we multiply the speed with 18/5.

To convert Km/h into m/s, we multiply the speed with 5/18.

Example:

10 m/s = 10x 18/5 = 36 km/h

72 km/h = 72 x 5/18 = 20 m/s

Average Speed: Objects around us most of the time, do not move with a constant speed. For
example, a car moving on a road keeps changing its speed depending on the traffic. Hence,
we calculate their average speed. It is the total distance travelled divided by total time taken.

Speedometer: Device installed in vehicles to measure the instantaneous speed.

Odometer: Device installed in the vehicle to ascertain the distance travelled by the vehicle.