NCERT class 7 science motion and time explaination
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Answer:
What is Motion?
If an object keeps on changing its position with time, it is said to be moving or in motion. Motion can be of different types:
Linear or straight in which the object travels in a straight line.
Circular in which the object travels along a circular path.
Curvilinear in which the object moves along a curve.
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Explanation:
Revision Notes on Motion and Time
What is Motion?
If an object keeps on changing its position with time, it is said to be moving or in motion. Motion can be of different types:
Linear or straight in which the object travels in a straight line.
Circular in which the object travels along a circular path.
Curvilinear in which the object moves along a curve.
Slow and Fast Motion
If one object covers a particular distance in less time and another object covers the same distance in more time then the first object is said to be moving slowly while the second object is said to be moving faster.
The Speed of an object
The distance travelled by an object in unit time is called its Speed.
Types of Speed:
Uniform Speed - When the object travels a fixed distance same time gaps, it is said to have a uniform speed.
Non-uniform speed - When an object covers different distances in different time gaps, it is said to have a non-uniform speed.
Average speed - The total distance travelled by an object divided by the total time taken by the object is called its average speed
Measuring Time
There are many events in nature that repeat after a time interval:
Morning – The rising of the sun
Day and Night – The time between the sunrise and sunset
Month – The time between two new moons
Year – The time the earth takes to complete its one revolution around the sun
Time measuring devices or clocks - Clocks use the concept of periodic motion to measure time. It means that it uses motion that repeats itself in equal amounts of time. There are different types of time measuring devices.
A simple pendulum contains a Bob. It is a metallic ball or a stone which is suspended from a rigid stand with the help of a thread.
Oscillatory motion - The to and fro motion of the pendulum is called as Oscillatory Motion. The bob of the pendulum does move from the centre (mean position) of the pendulum to its extreme positions on the other side.
Oscillation - When the bob moves from its centre (mean position) to its extreme ends it is said to complete one oscillation.
Time Period of a pendulum - The time taken by the pendulum bob to complete one oscillation is called its Time Period.
Speedometer - It is a device which is used in vehicles such as cars and trucks which measures the speed in kilometer per hour.
Odometer - It is a device which measures the distance travelled by a vehicle in meters or kilometers.
Distance-time Graph
A graph which represents the distance travelled by an object with respect to time is called a distance-time graph.
To find the speed of the distance-time graph
Speed = distance/time = (final position of object – initial position of object)/time taken by object
Also, the speed of the distance-time graph can be calculated by the Slope of a graph. The steeper the slope of the graph, the more is the speed of the object. For example, in the graph given below object A has a steeper slope. This means that object A is moving at a higher speed than object B.