Tiêu đề Chapter - 1 Motion.pdf ✅

Motion ● To describe the position of an object we need a reference point or origin. An object may seem to be moving to one observer and stationery to another. ● Example: A passenger inside a bus sees the other passengers to be at rest, whereas an observer outside the bus sees the passengers to be in motion. ● In order to make observations easy, a convention or a common reference point or frame is needed. All objects must be in the same reference frame. Rest and Motion ● If the position of an object does not change as time passes, then it is said to be at rest. If the position of an object changes as time passes, then it is said to be in motion. ● An object can be at rest with respect to one thing and in motion with respect to some other thing at the same time. So, the states of rest and motion are relative only. ● To locate the position of an object, we have to choose some suitable reference point called the origin. Distance and Displacement ● The distance travelled by an object is the length of the actual path traversed by the object during motion. It is a scalar quantity. ● The displacement of an object in motion is the shortest distance between the initial position and the final position of the object. It is a vector quantity.
ChemContent ● The distance travelled by an object in motion can never be zero or negative. ● The displacement of an object can be positive, zero or negative. Never can the distance travelled be less than the displacement. ● Both distance and displacement have the same units. Magnitude ● Magnitude is the size or extent of a physical quantity. In physics, we have scalar and vector quantities. ● Scalar quantities are only expressed as magnitude. E.g.: time, distance, mass, temperature, area, volume ● Vector quantities are expressed in magnitude as well as the direction of the object. E.g: Velocity, displacement, weight, momentum, force, acceleration, etc. Time and speed Time is the duration of an event that is expressed in seconds. Most physical phenomena occur with respect to time. It is a scalar quantity. Speed is the rate of change of distance. If a body covers a certain distance in a certain amount of time, its speed is given by Speed = Distance Time Uniform and Non-uniform Motion ● An object is said to be in uniform motion if it travels equal distances in equal intervals of time, howsoever small the intervals may be. ● An object is said to have non-uniform motion if it travels unequal distances in equal intervals of time. Uniform Motion: Definition: This type of motion is defined as the motion of an object in which the object travels in a straight line and its velocity remains constant along that line as it covers equal distances in equal intervals of time, irrespective of the duration of the time.

ChemContent ● If ‘s’ is the distance travelled by a body in time ‘t’, then its speed ‘v’ ’ is given as v = s\t ● Speed of a body is a scalar quantity. It can be zero or positive but can never be negative. ● If a body covers equal distances in equal time intervals, howsoever small the intervals may be, then it is said to have uniform speed (or constant speed). ● If a body covers unequal distances in equal time intervals, however small the intervals may be, then it is said to have non-uniform speed (or variable speed). ● For bodies moving with non-uniform speed, we describe the rate of motion in terms of their average speed. Velocity ● Velocity of a body is defined as the distance travelled by the body in unit time in a given direction. ● The SI unit of velocity is the same as that of speed, i.e. metre/second (m/s). where v is velocity and s is displacement of the body in time t. ● Velocity of a body is a vector quantity. It can be positive, negative or zero. ● A body is said to be moving with uniform velocity (or constant velocity) if it travels along a straight line, covering equal distances in equal intervals of time, howsoever small these intervals may be. ● A body is said to be moving with non-uniform velocity (or variable velocity) if it covers unequal distances in a particular direction in equal intervals of time or if the direction of motion of the body changes. ● When the velocity of a body is changing at a uniform rate over a period of time, the average velocity for that time period is given by the arithmetic mean of the initial and final velocity of the body.