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Motion is the change in the position of an object with respect to time. It refers to the movement of an object with respect to some stationary object. A person walking on the road, a pen falling from the table, a dog running on the road, etc. are all examples of motion.
- Everything in the universe is in a state of motion of some sort.
- Distance, Speed, Displacement, and Time are the four parameters that are used to describe the motion of an object.
- Motion of an object depends on the type of force acting on the object.
- Linear Motion, Rotatory Motion, and Oscillatory Motion are the three main types of motion based on movement.
Read More: NCERT Solutions for Class 9 Science Motion
Key Terms: Motion, Distance, Displacement, Speed, Uniform Motion, Non-Uniform Motion, Laws of Motion, Motion in a Straight Line
What is Motion?
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Motion is the change in the position of an object with respect to its surroundings in a given time interval. Everything in the universe is in a state of continuous motion. Atom, the fundamental particle of matter, is in constant motion too. Thus, motion can be slow, but it exists.
- The states of rest and motion are said to be relative to each other.
- An object may appear to be moving to one observer, while it appears to be stationary to another.
Car in Motion
For example, when a car is moving on the road,
- Trees on the road appear to be moving backward to the passenger.
- A person standing on the road finds the car and its passengers moving forward.
- A person inside the moving car finds his fellow passenger at rest.
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Factors Affecting Motion
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Motion of an object is affected or described by four major factors which are as follows:
- Distance (d)
- Displacement (s)
- Speed (v)
- Time (t)
Distance
Distance is the complete path travelled by an object during a given period of time.
- It is a scalar quantity, with only magnitude and no direction.
- Distance is always positive in nature.
- It gives complete information about the route being followed by an object from one point to another.
- It can be calculated for linear as well as zigzag paths.
- Distance is denoted by the symbol ‘d’ and the SI unit of distance is ‘meter’ (m).
The distance traveled by an object is given by the formula:
| Distance = Speed x Time |
Displacement
Displacement is the shortest possible distance between the initial and final position of an object.
- It has direction as well as magnitude, thus, it is a vector quantity.
- Displacement of an object could be positive, negative as well as zero.
- It depends upon the direction in which the object is traveling.
- It does not provide complete information about the route being traveled.
- Displacement is denoted by ‘s’ and is also measured in ‘meters’ (m).
For any object in motion, the Displacement Formula is given as
| Δx = xf − x0 |
Where
- xf: Final position on the Object
- x0: Initial position of the Object
Read More: Unit of Displacement
Speed
Speed is the rate at which an object or body moves from one location to another.
- It is the ratio of the distance covered by an object to the total time taken to cover that distance.
- It is a scalar quantity, with only magnitude and no direction.
- The SI unit of speed is ‘meters per second’ (m/s).
Speed is calculated using the given formula,
| \(Speed = {Distance \over Time}\) |
Read More: Difference between Speed and Velocity
Time
Time is integral for evaluating the change in state and motion of the objects.
- It is defined as the interval over which any object changes its motion, orientation, and structure.
- The SI unit of time is the second (s).
- Time and motion are interdependent on each other because when a body moves, its position changes with time.
- The dimensional formula of time is [M0L0T1].
Motion
Motion in a Straight Line
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Motion of an object is called rectilinear motion when it moves in a straight line. Motion in a straight line states that the motion of a given object is in a particular straight line, and uses only one dimension. An example of such motion would be the motion of an automobile on the highway.
Motion in a Straight Line can be of two types namely:
- Uniform Motion in a Straight Line
- Non-Uniform Motion in a Straight Line
Uniform Motion in a Straight Line
If a body travels in a straight line and covers an equal amount of distance in an equal interval of time, it is said to have uniform motion.
Example: A train covers 30 km in the first hour, another 30 km in the second hour, again 30 km in the third hour, and so on. The motion of the train is uniform motion as it covers an equal distance in equal intervals.
Uniform Motion
Non-Uniform Motion in a Straight Line
Non-Uniform Motion is a type of motion in which an object moves at different speeds. In simple words, when an unequal distance is covered in equal intervals of time by an object, it is said to be in non-uniform motion.
Example: A car covers 40 km in the first hour, 30 km in the second hour, 25 km in the third hour, and so on till it reaches its destination. Here, the motion of the car is said to be non-uniform as it is traveling unequal distances in equal intervals of time.
Non-Uniform Motion
Read More: Motion Class 9 Important Questions
Types of Motion
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Motion differs from object to object and can be classified into various types depending upon the same. The various types of motion are as follows:
- Rotational Motion: In this motion, an object moves along a circular path about a fixed axis.
- Translational Motion: It is the motion in which an object moves along a path in any of the three dimensions.
- Linear Motion: It is a sub-type of translational motion in which an object moves in a single direction along a single dimension.
- Periodic Motion: It refers to the motion that repeats itself after certain intervals of time.
- Simple Harmonic Motion: It is a motion where a restoring force acts in the direction opposite to the direction of motion of the object.
- Projectile Motion: In this motion, there is a horizontal displacement as well as vertical displacement.
- Oscillatory Motion: It is a motion that is repetitive in nature within a given time interval.
Examples of Motion
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Motion is present everywhere in the universe. It is seen in the particles of matter, bodies, radiation, radiation fields, radiation particles, curvature, and space-time.
- Motion is seen in daily activities such as walking, running, playing, etc.
- Breathing, which is the flow of air in and out of our lungs is also an example of motion.
- A car or an automobile moving from one place to another is motion.
- The revolution of planets around the sun is another instance of motion.
Laws of Motion
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Sir Issac Newton gave the foundational principles for motion, which are popularly referred to as ‘Newton’s Laws of Motion’. There are three laws of motion given by Newton which are described as follows:
- Newton’s First Law of Motion: Any object will continue to be in motion or rest unless a net external force acts on it.
- Newton’s Second Law of Motion: For an object with a certain mass, the greater the mass of the object, the greater will be the force required to accelerate the object.
- Newton’s Third Law of Motion: To every action, there is an equal and opposite reaction.
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| Related Topics | ||
|---|---|---|
| Speed, Distance and Time Formula | Velocity Formula | Law of Inertia |
| Average Speed Formula | Molecular Motion | Average Velocity Formula |
Difference between Distance and Displacement
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Distance and Displacement are two important terms in motion that are often used interchangeably, however, they are two different parameters to measure motion. The difference between distance and displacement is as follows:
| Distance | Displacement |
|---|---|
| It is the complete length of the path traveled by an object. | It is the shortest distance between the initial and the final position of an object. |
| It is either positive or zero. | Displacement can be positive, negative, or zero. |
| It is a scalar quantity with only magnitude. | It is a vector quantity with both direction and magnitude. |
| It is denoted by the symbol ‘d’. | It is denoted by the symbol ‘s’. |
| Distance Formula: Speed × Time | Displacement: Velocity × Time |
Graphical Representation of Motion
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Graphical Representation of Motion refers to the process of depicting the motion of an object pictorially using line graphs. The three main types of graphs in Graphical Representation of Motion are:
- Distance-Time Graph
- Velocity-Time Graph
- Acceleration-Time Graph
Distance-Time Graph
Distance is defined as the total path covered by an object. In the distance-time graph, the time is taken on the x-axis and the distance on the y-axis. The slope of the distance-time graph gives us the speed of the object.
Distance-Time Graph for Body at Rest
Distance-Time Graph for Rest
Distance-Time Graph for Uniform Motion
Distance-Time Graph for Uniform Motion
Distance-Time Graph for Non-Uniform Motion
Distance-Time Graph for Non-Uniform Motion
Velocity-Time Graph
Velocity-Time Graph shows the change in the velocity of an object with time. In the velocity-time graph, the time is taken on the x-axis and the velocity on the y-axis. The slope of the velocity-time graph gives us the acceleration of an object.
Velocity-Time Graph for Uniform Velocity
Velocity-Time Graph for Uniform Velocity
Velocity-Time Graph for Acceleration
Velocity-Time Graph for Acceleration
Velocity-Time Graph for Retardation
Velocity-Time Graph for Retardation
Acceleration-Time Graph
The acceleration-time graph describes whether the velocity of an object is increasing or decreasing. The time is taken on the x-axis, and the acceleration is taken on the y-axis.
Things to Remember
- Motion is the change in the position of an object over time.
- When an equal distance is covered in equal intervals by an object, it is said to be in uniform motion.
- When an unequal distance is traveled in equal intervals of time, the object is said to be in non-uniform motion.
- Distance is the total length of the path covered by an object in a given time interval.
- The shortest path or distance between an object's initial and final positions is known as displacement.
- Speed of an object is defined as the distance it travels in a given amount of time.
- Distance-Time Graph, Velocity-Time Graph, and Acceleration-Time Graph are the three main graphs used in motion.
Sample Questions
Ques. What is Motion? What are the two main types of motion? (3 Marks)
Ans. Motion is defined as the change in the position of an object with respect to time. There are two types of motion:
- Uniform Motion
- Non-Uniform Motion
When an object covers equal distances in equal intervals of time, it is said to be in uniform motion. While when an object covers unequal distances in equal intervals of time, it is said to be in non-uniform motion.
Ques. An artificial satellite is moving in a circular orbit with a radius of 42250 km. Calculate its speed if it takes 24 hours to revolve around the earth. (3 Marks)
Ans. Given that,
- Radius of the circular orbit, r = 42250 km
- Time is taken to revolve around the earth, t = 24 h
Speed of Satellite = v = (2πr)/t
Speed of Satellite = (2 x 3.14 x 42250)/24 = 1.105 x 104 km/hr = 3.069 km/s
Hence, the speed of the artificial satellite is 3.069 km/s.
Ques. Distinguish between speed and velocity. (3 Marks)
Ans. The difference between speed and velocity is as follows:
| Speed | Velocity |
|---|---|
| Speed is the distance traveled by an object in a given interval of time. It does not have any direction. | Velocity is the displacement of an object in a given interval of time. It has a unique direction. |
| Speed = Distance/Time | Velocity = Displacement/Time |
| The speed of an object can never be negative. At the most, it can become zero. This is because the distance traveled can never be negative. | The velocity of an object can be negative, positive, or equal to zero. This is because displacement can take any of these three values. |
Ques. When will you say a body is in
(i) Uniform Acceleration
(ii) Non-uniform Acceleration (3 Marks)
Ans. (i) A body is said to have uniform acceleration if it travels in a straight path in such a way that its velocity changes at a uniform rate, i.e., the velocity of a body increases or decreases by equal amounts in an equal interval of time.
(ii) A body is said to have non-uniform acceleration if it travels in a straight path in such a way that its velocity changes at a non-uniform rate, i.e., the velocity of a body increases or decreases in unequal amounts in an equal interval of time.
Ques. A train starting from a railway station and moving with uniform acceleration attains a speed of 40 km h-¹ in 10 minutes. Find its acceleration. (3 Marks)
Ans. Given that,
- Initial Velocity of Train, u = 0 (since the train is initially at rest)
- Final Velocity of Train, v = 40 km/h = 11.11 m/s
- Time taken, t = 10 min = 10 × 60 = 600 s
Acceleration, a = (v-u)/t
a = (11.11 - 0)/600 = 0.0185 m/s2
Hence, the acceleration of the train is 0.0185 m/s².
Ques. A racing car has a uniform acceleration of 4 m s-². What distance will it cover in 10 s after the start? (3 Marks)
Ans. According to the question,
- Initial velocity of the racing car, u = 0 (since the racing car is initially at rest)
- Acceleration, a = 4 m/s²
- Time taken, t = 10 s
According to the second equation of motion,
s = ut + 1/2at2
Where s is the distance covered by the racing car. Thus,
s = 0 + ½ x 4 x 102 = 400/2 = 200 m
Hence, the distance covered by the racing car 10 s from start is 200 m.
Ques. Joseph jogs from one end A to the other end B of a straight 300 m road in 2 minutes 30 seconds and then turns around and jogs 100 m back to point C in another 1 minute. What are Joseph’s average speeds and velocities in jogging
(a) From A to B
(b) From A to C (5 Marks)
Ans. (a) From end A to end B
- Distance covered by Joseph while jogging from A to B = 300 m
- Time taken to cover that distance = 2 min 30 seconds = 150 s
Average Speed = Total Distance Covered / Total Time Taken
Average speed = 300 / 150 = 2 m/s
Average Velocity = Total Displacement/Total Time
- Displacement = Shortest distance between A and B = 300 m
- Time interval = 150 s
Average velocity = 300 / 150 = 2 m/s
The average speed and average velocity of Joseph from A to B are the same and equal to 2 m/s.
(b) From end A to end C
Average Speed = Total Distance Covered / Total Time Taken
- Total Distance Covered = Distance from A to B + Distance from B to C = 300 + 100 = 400 m
- Total Time Taken = Time taken to travel from A to B + Time taken to travel from B to C = 150 + 60 = 210 s
Average Speed = 400 / 120 = 1.90 m/s
Average Velocity = Total Displacement/Total Time
- Displacement from A to C = AC = AB − BC = 300 − 100 = 200 m
- Time interval = time taken to travel from A to B + time taken to travel from B to C = 150 + 60 = 210 s
Average velocity = 200 / 210 = 0.95 m/s
The average speed of Joseph from A to C is 1.90 m/s and his average velocity is 0.95 m/s.
Ques. A tortoise moves a distance of 100 meters in 15 minutes. What is the average speed of a tortoise in km/h? (3 Marks)
Ans. Given that,
- Total distance = 100m = 0.1 km
- Total time taken = 15 minutes = 15/60 = 0.25 hour
Average Speed = Total Distance Travelled/ Total Time Taken
Average Speed of Tortoise = 0.1/0.25 = 0.4km/h
Ques. If a sprinter runs a distance of 100 meters in 9.83 seconds, calculate his average speed in km/h. (3 Marks)
Ans. Given that,
- Total distance travelled = 100m
- Total time taken = 9.83 sec
Average Speed = Total Distance Travelled/ Total Time Taken
Average Speed of Sprinter = 100/9.83 = 10.172m/s
Average speed in km/h = 10.172 x (3600/1000) = 36.62 km/h
Ques. How is distance different from displacement? (2 Marks)
Ans. The main difference between distance and displacement is direction. In distance, the direction is not required for the calculation, while one needs direction to calculate displacement. Displacement is a vector quantity while distance is a scalar quantity. Distance offers a complete information about the route being traveled which is not offered by displacement.
Ques. What are Vector and Scalar Quantities? (1 Mark)
Ans. The term "vector" refers to a quantity with both magnitude and direction. For example, force, position, and displacement. A scalar quantity is one that has no related direction. For example, mass, temperature, and time.
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