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## Revision Notes of Ch 13 Motion and Time Class 7th Science

Topics in the chapter
• What is motion?
• Speed
• Types of speed
• Measuring time
• Oscillatory motion
• Units to measure time speed
• Distance-time graph
• Finding speed from distance-time graph
What is motion?

→ When an object keeps on changing its position with time it is said to be motion.

Types of motion

(i) Linear: Also called straight motion in which the object travels in a straight line.

(ii) Circular motion: The object travels along a circular path

(iii) Curvilinear motion: The object moves along a curve.

Speed

It is a distance moved by an object in a unit time is called speed.
Speed helps us to decide which object is moving faster than other.
The basic unit of speed is meter per second (m/sec).
Speed of object = distance travelled/ time taken

Types of speed

(i) Uniform speed: Object travels a fixed distance on same time gap.

(ii) Non-uniform speed: Object covers different distance in different time gaps.

(iii) Average speed: Total distance is divided by total time taken by object.

Measuring time

Time measuring device: The time measuring device i.e., clocks use the concept of periodic motion to measure time which means it uses motion that repeats itself in equal amount of time.

Types of time measuring device

Sundial
Sand clock
Water clock
Pendulum clock
Quartz clock

Oscillatory motion

→ The motion of a pendulum in to and from is called as oscillatory motion.

Time period of a pendulum: The time taken by a pendulum bob to complete one oscillation is called its time period.

Units to measure time speed

Speed = distance/time (m/s)

→ Speedometer: It is a device which is used to measure the speed in kilometer per hour.

→ Odometer: The device which is used to measure the distance travelled by a vehicle in meters or kilometers.

Distance-time graph

The graph which represents the distance travelled by an object with respect to time is called distance-time graph.

Finding speed from distance-time graph

Speed= distance/time = (final position of object – initial position of object)/time taken.

Also, slope of the graph calculate the speed of the distance-time graph.

The steeper the slope of the graph the more is the speed of object.

NCERT Solutions of Motion and Time Class 7