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MOTION , PART, CLASS IX SCIENCE
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What is Physics?, , The word ‘PHYSICS’ is derived from the word “Phugus” which means “Nature.”, , Physics is the branch of science that deals with , the study of natural phenomenon. , , Father of Physics- Albert Einstein, Father of Ancient Physics- Sir Issac Newton, Father of Modern Physics- Galelio Galilei
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WHAT is a UNIT ?, , , , , , , , , A unit is the standard measure of the quantity., , , , Two Types of Units–, Fundamental units , Derived units
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Frame of Reference
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Frame of Reference -, In order to know the change in position of an object, a reference point is required. , Point O in the figure is the reference point or Origin and together with three axes, this system is called the coordinate system., A coordinate system with time frame is called frame of reference., , In a moving car, for the frame of reference outside the car, it appears moving. While for the frame of reference inside the car, the car appears stationary., , Objects changing positions with time with respect to the frame of reference are in motion while those which do not change position are at rest.
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Concept of Rest and Motion, Rest – If a body does not change its position with time., E.g. – Table , Chair etc., Motion – If a body changes its position w.r.t. its surroundings with time. , e.g. – Moving Fan, walking etc., Distance – It is the actual length of path travelled., Displacement – It is the shortest path or the distance between initial and final point.
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In 1 revolution , , , Distance = Circumference of circle =2πr but Displacement = 0, EXAMPLE -3
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TYPES OF MOTION , TRANSLATORY MOTION , CIRCULAR MOTION
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TYPES OF CIRCULAR MOTION
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Questions:, 1.Meaning of Phugus …………….., 2.Who is the father of Physics?, 3.The units used to measure derived quantities are known as, a. square units, b. derived units, c. base units, d. scalar units, 4. The S.I unit of Luminous Intensity…….., 5. Which of the following is a physical quantity that has a magnitude but no direction?, a. Vector, b. Scalar, c. Resultant, d. Frame of Reference, 6. Acceleration is a scalar or a vector quantity………., Answers: 1.Nature 2. Albert Einstein 3. b 4. Candela 5. b 6. Vector
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v = 500/10, = 50m/sec., E.g., Q.
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Average Speed, The average speed of a body is the total distance travelled by the total time taken to cover this distance., Average speed= Total Distance travelled , Total Time taken, EXAMPLE -1 , You walk 60 m at a speed of 3m/s and then run 140m at a speed of 7m/s along a straight track. Find the average speed?, Solution: s1= 60 m & v1 = 3 m/s , as, t1= s1 / v1, therefore, t1 = 60/3=20s , Now s2= 140 m & v2 = 7 m/s , i.e. t2 = s2 / v2 = 140/7 = 20 s, as Average Speed = s1 + s2 / t1 + t2 = 60+140 / 20+20, = 200 / 40 = 5 m/s
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Average Velocity, The average velocity of a body is the total displacement travelled by the total time taken to cover this distance., Average velocity= Total Displacement = u+v, Total Time taken 2, Question:, 1. If Ananya was able to travel 6 km in North in 2 hour in his car. What was her velocity?, Solution; Velocity= Displacement, Time, = 6 km in North , 2 hour, = 3km/h in North, 2. A car travels 300 m in East in 3 s. What was the velocity of the car ?, 3. If Atul travels 40 m west in 20 sec and 80 m east in 30 sec, then find its average velocity?
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EXAMPLE –, If the velocity of the car reduced to 80 m/s from 120 m/s in 8 seconds on applying breaks . Calculate its acceleration., Solution:, Here, V= 80m/s, U= 120 m/s, t = 8 sec, as we know, acceleration = v – u , t , therefore, acceleration = 80-120 = -40 = -5 m/s2, 8 8, Since acceleration is negative so it is called Retardation.
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Equations of Motion -
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DERIVATION OF FIRST EQUATION OF MOTION ( V = u+at ), Consider a body of mass “m” having initial velocity “u”. Let after time “t” its final velocity becomes “v” due to uniform acceleration “a”., Now as we know that, Acceleration = change in velocity/Time taken, Acceleration = Final velocity-Initial velocity / time taken, a = v-u , t, at = v-u, or v = u + at, This is the first equation of motion.
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DERIVATION OF SECOND EQUATION OF MOTION (S=ut+1/2 at2), Consider a body of mass “m” having initial velocity “u”. Let after time “t” its final velocity becomes “v” due to uniform acceleration “a”. Let the distance travelled by the body be “s”. , Now As we know that,, Distance = Average velocity X Time, Also, Average velocity = u+v, 2, Distance (s) = u+v …….eq.(1), 2t
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DERIVATION OF THIRD EQUATION OF MOTION (V2 = u2 +2as), Consider a body of mass “m” having initial velocity “u”. Let after time “t” its final velocity becomes “v” due to uniform acceleration “a”. Let the distance travelled by the body be “s”., , As know that, V = u + at, v-u = at , or t = (v-u)/a ………..eq.(1), By using second equation of motion, S = ut +1/2 at2 ……eq.(2) , Substituting the value of “t” from eq. (1) in eq. ( 3), => S = u(v-u) + 1 a* (v-u)2 , a 2 a2
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Questions :, 1. A moving train is brought to rest within 20 s by applying breaks. Find the initial velocity, if the retardation due to brakes is 2m/s-2., Solution: u= ?, v=0, a=-2m/s2, t= 20s, By using formula, v= u + at, 0= u + (-2)(20), 0= u - 40, u= 40 m/s
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2. A scooter moving at a speed of 10m/s is stopped by applying brakes which produce a uniform acceleration of -0.5m/s2. How much distance will covered by the scooter before it stops?, Solution: u = 10m/s, v = 0, a = -0.5m/s2, s = ?, By Formula, v2 = u2 + 2as, (0)2 = (10)2 + 2(-0.5)s, 0 = 100 – s, s = 100m
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Home Work -, 1.A car travels a distance of 100 kilometers in 4 hours, then the speed of this car is given by:, 2. A car travels 30 km at a uniform speed of 40 km/h and the next 30 km at a uniform speed of 20 km/h . Find the average speed., 3. A car travels a distance of 200 km from Delhi to Noida towards North in 5 hours. Calculate the velocity of the car., 4. A racing car has a uniform acceleration of 4m/s2. What distance will it cover in 10 s after the start?, Answers:, 25 km/h 2. 26.6 km/h 3. 40 km/h towards North , 4. 200m
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Speed Time Graph
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RESULTS –, 1)Area under s-t graph = distance travelled by the body, 2)Slope under s-t graph = speed
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RESULTS –, 1)Area under v-t graph = distance travelled by the body, 2)Slope under v-t graph = acceleration, SPEED –TIME GRAPHS
