notes for science science motion and time
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Motion and Time Class 7 Notes Science Chapter 13
April 24, 2019 by Sastry CBSE
CBSE Class 7 Science Notes Chapter 13 Motion and Time Pdf free download is part of Class 7 Science Notes for Quick Revision. Here we have given NCERT Class 7 Science Notes Chapter 13 Motion and Time.
CBSE Class 7 Science Notes Chapter 13 Motion and Time
In our daily life routine, we usually see some objects at rest and others in motion like birds fly, fish swimming, planets moving around the sun, etc., are all in motion. When an object changes its position with time, we often perceive an object to be in motion, e.g. when the position of a car changes with time, we say that the car is moving or the car is in motion.
Types of Motion
The motion of all the objects are not of the same type. There are four different types of motion shown by the different objects.
Rectilinear motion: The motion possessed by the body moving along a straight line path, is called rectilinear motion,
e.g. the motion of a train on a straight bridge.
Circular motion: The motion possessed by a body when it moves along a circular path, is called circular motion,
e.g. the motion of a child in a merry-go-round, motion of the earth around the sun in a circular orbit.
Rotational motion: The motion possessed by a body when it spins about a fixed axis, is called rotational motion,
e.g. the motion of the earth about its axis, spinning top, the motion of blades of a fan.
Periodic motion: The motion which repeats itself after regular intervals of time, is called periodic motion,
e.g. the motion of the swing, to and fro motion of a simple pendulum.
Slow or Fast Motion
An object which takes a long time to cover a certain distance is known as slow while the other object which takes shorter time to cover the same distance is known as fast, e.g. if your school is at a distance of 5 km from your home and you want to go to school by bicycle, then it may take about 25 min to reach the school and if you go to school by school bus, then the same distance can be covered only in 10 min.
It means that a bicycle takes a longer time than the bus.
Thus, the most convenient way to determine which of the two objects is moving faster is to compare the distance moved by them in a unit time which is known as speed.
Speed
The distance travelled by an object per unit time (either in one hour, in one minute or in one second) is known as speed of the object. A slow moving object is said to have a low speed and a fast moving object is said to have high speed. So, if we know the distance covered by two buses in one hour, then we can answer which one is slower. Therefore, the formula for calculating the speed of an object can be given by
Speed = DistancetravelledTimetaken
e.g. If a car travels a distance of 100 km in 2 h, then the speed of this car is given by
Speed = 100km2h = 50 km/h
It shows that the car will travel a distance of 50 km in 1 h. It does not matter if a car seldom moves with a constant speed for one hour as it starts moving slowly and then picks up speed. So, when we say that the car is moving with a speed of 50 km/h, then we do not bother whether the car has been moving with a constant speed or not during that hour. Therefore, the speed calculated here is the average speed of the car.
Motion is the change in the position of an object with respect to its surroundings. It is the distance moved by an object or its displacement. The distance moved by an object in a unit time is called its speed. The speed of an object helps to compare whether a body is moving fast or slow.