CBSE Class 7 Science Chapter 13 Notes Motion and Time
Motion and Time Class 7 Notes Understanding the Lesson
1. The act or process of moving or of changing position or change of posture or a gesture is called motion.
2. Motion of objects are of two types-motion of some objects are slow while that of some others are fast.
3. Objects which take a longer time to cover a certain distance is called slow whereas another object which takes a shorter time to cover the same distance is said to be
4. The speed of an object is defined as the distance travelled by the object in unit time.
Speed = \(\frac{\text { Distance travelled }}{\text { Time taken }}\)
5. The SI unit of speed is metre per second (m/s).
6. If the speed of an object moving along a straight line keeps changing, its motion is said to be non-uniform motion.
7. If an object moving along a straight line with a constant speed, its motion is said to be in uniform motion.
8. The average speed of a body can be defined as the total distance travelled divided by the total time taken. ,
Thus, Average speed = \(\frac{\text { Total Distance travelled }}{\text { Total Time taken }}\)
9. A simple pendulum consists of a small metallic ball, called the bob, suspended from a rigid stand by a thread.
10. The time taken by the pendulum to complete one oscillation is called its time period.
11. Speedometer is an instrument on a vehicle’s dashboard which indicates the speed of the vehicle when it is running. It records the speed directly in km/h.
12. Odometer is an instrument for measuring the distance travelled by the vehicle. It records the distance travelled by the vehicle in kilometres.
13. The basic unit of time is second.
14. A graph is used to study the relation between two inter-dependent physical quantities.
15. The quantity in the graph that is made to alter at will is called independent variable and the other quantity which varies as a result of this change is known as dependent variable. The graph may be a straight or curved line.
16. The distance-time graph for the motion of an object moving with a constant speed is a straight line.
Class 7 Science Chapter 13 Notes Important Terms
Bar graph: A graph in which statistical data are represented in form of bars of different heights.
Graphs: A graph is a mathematical relation between two inter-dependent physical quantities.
Non-uniform motion: When a body covers unequal distances in equal intervals of time or equal distances in unequal intervals of time, then it is said to be in non-uniform motion.
Oscillatory motion: The to and fro motion of a simple pendulum about its mean position is called oscillatory motion.
Speed: The distance travelled per unit time is known as speed.
Speed = \(\frac{\text { Distance Covered }}{\text { Time taken }}\)
Time period: The time taken by a pendulum for one oscillation is called its time period.
Uniform motion: Uniform motion can be defined as the motion in which body travels equal distances in equal intervals of time.
Unit of time: The SI unit of time is second.