Jun 08, 2022, 16:45 IST
A body is said to be at rest if it does not changes its position with respect to a fixed point in its surrounding. Example: A book lying on the table will not change its position if it is not disturbed and will be considered to be in a state of rest
A body is said to be at rest if it changes its position with respect to a fixed point/object in its surrounding. Example: A flying bird, a moving bus, a sailing ship, a walking man, etc. Example: pendulum of wall clock oscillating about the lower most point.
Different kinds of motions can be classified in to the following types:
Consider an object moving along a straight line. Let it travel 5 m in the first second, 5 m more in the next second, 5 m in the third second and 5 m in the fourth second. In this case, the object covers 5 m in each second. As the object covers equal distances in equal interval of time, it is said to be in uniform motion. For example, a train moving straight in a particular direction at a constant speed.
The time interval in this motion should be small. In our day-to-day life, we come across motions where objects cover unequal distances in equal intervals of time, it is said to be in non-uniform motion. For example, when a car is moving on a crowded street or a person is jogging in a park.
Speed is a physical quantity which gives us an idea about the motion of a body. Suppose we want to compare the motions of the cycle and car on the road. We see that car travels faster than the cycle in the same time-period. Hence, we say that the car moves faster than the cycle.
The distance travelled by a body per unit time is known as the speed of a body.
Speed (s) = Distance travelled (d) / Time taken (t)
Speed is a scalar quantity. Its S.I unit is meter per second (m/s).
Velocity is a physical quantity which gives us an idea about the motion of a body along with its direction. The velocity of a body is the distance travelled by the body in unit time and in a given direction. Hence, Velocity can be defined as displacement per unit time.
Velocity = Displacement / Time
Velocity is a vector quantity. Its S.I unit is meter per second (m/s).
Acceleration: A car starts from rest and attains a constant velocity, say, 50 km/hr. It runs at that velocity for some time. The driver now wants to slow down the car and hence reduces the velocity, so that finally it becomes zero. The various changes in velocity are expressed in terms of acceleration. It is therefore, defined as the rate of change of velocity of a body.
Acceleration = Change in velocity/ Time Acceleration = (Final velocity - Initial velocity)/ Time
Acceleration (a) = (v – u) / t
Acceleration is a vector quantity. Its S.I unit is meter per (second) 2 i.e (m/s 2 ).
Do solve questions given in the NCERT text book with the help of NCERT solutions for class 7 Science . If any students need to take the online test to check their concepts or undertstanding then they can visit Quiz for Motion and Time .
Students can alse get Science Formula for Class 7 from here.
Find Below Short Notes of chapter-Motion and Time