**Chapter 8 Motion Class 9 Notes**

**Topics to be discussed –**

Here is the list of topics that we are going to study in this Motion Chapter of Class 9.

- What is Motion?
- Distance and Displacement
- Physical Quantities
- Types of Motion
- Speed
- Acceleration
- Distance time Graph
- Equations of uniform accelerated Motion
- Derivation of Equations of Motion by Graphical Method
- Uniform Circular Motion

**What is Motion?**

A body is said to be in motion, if its position changes with time, with respect to a reference point.

**What is Distance?**

Distance between two points is the total path length covered in travelling between these two points.

Example- Let say AB = 4 m and BC = 7 m, then **distance **is the **total path travelled/covered**, i.e., AB+BC = 4 m + 7 m = 11 m.

**SI Unit**of Distance is**metre**(m).

**What is Displacement?**

It is th estraight line path between initial and the final positions. It is the lenght od shortest line between initial and final position.

**SI Unit**of displacement is**metre (m).**

**Physical Quantities**

There are two types of physical quantities –

**Scalar Quantities:**defined by only**magnitude**. Example- distance**Vector Quantites:**defined by both**magnitude**and**direction**. Example- displacement.

**Types of Motion**

- Uniform Motion
- Non-Uniform Motion

**Uniform Motion**

**What do you understand by Uniform Motion?**

When an object covers equal distance is covered in equal interval of time, it is said to be in uniform motion.

**What do you understand by Non-Uniform Motion?**

When unequal distances are covered in equal interval of time.

**What is Speed?**

The distance covered per unit time is called speed.

Example- distance is 10 cm, and time taken is 2 seconds.

Speed = Distance/time = 10/2 = 5 m/s.

- The
**SI Unit**of Speed is**metre/second (m/s).** - Speed is a
**scalar quantity.**

**What is Average Speed?**

The average speed of a body is the total distance travelled divided by total time taken to cover this distance.

**Also Read: Physics Numerical Class 9 Motion**

**Average Speed**is a**non-uniform motion.**

**What is Velocity?**

Velovity of a body is the distance travelled per unit time in a given direction.

or

Velocity of a body is the displacement produced per unit time .

**Velocity = Displacement/time taken**

**What is an Odometer?**

Odometer is a device or an instrument that measures the distance covered by a vehicle.

**What is a Speedometer?**

Speedometer is a device or an instrument that measures speed.

**Average Velocity = (Initial Velocity + Final Velocity)/2**

**What is Acceleration?**

**Acceleration **of a body is defined as the rate of change of its velocity with time.

or, Accelration = Change in velocity/2

**Acceleration**is a vector quantity.**SI Unit**of accelration is**metre/second² (m/s²).**

**Graphical Representation of Motion**

**Distance-Time Graphs**

Important Points:

- The distance time grpah of a body moving at uniform speed is always a straight line.
- It can be used to calculate the speed of a body.
- If the speed of a body is non-uniform, then the graph between distance travelled and time is a curved line (parabola).
- If the displacement time graph is drawn, then it will specifically repreesnt velocity.
- The speed-time graph is also known as velocity time graph.

**Equations of Uniformly Accelerated Motion**

**First Equation of Motion**

The first eqaution of Motion is – **v = u + at**

where, v = Final velocity, u = Initial Velocity, t = time, and a = acceleration

- It gives the velocity acquired by a body in time t.

**Second Equation of Motion**

It gives the distance travelled by body in time ‘t’.

The 2nd equation of motion is – **s = ut + ½at²**

**Third Equation of Motion**

The third equation of motion is – **v² = u² + 2as**

- It gives the velocity acquired by a body in travelling a distance ‘s’.

**Note: For Derivation Watch the videos below**

**Derivation of Equations of Motion by Graphical Method**

Watch The video for Derivation.

**What is Uniform Circular Motion?**

When a body moves in a circular path with a uniform speed (constant speed), its motion is called unifom circular motion.

**Examples of Uniform Circular Motion**

- Artificial satellites move in a uniform circular motion around the earth.
- The moon moves in uniform circular motion around the earth.
- The earth moves around the sun in uniform circular motion.
- An athelete (or cyclist) moving on a circular track with a constant speed exhibits uniform circular motion.
- The tip of a seconds’ hand of a watch exhibits uniform circular motion on the circular dial of the watch.

You can also downlaod the Motion Notes PDF from the below link.

**Download the Motion Class 9 Notes Pdf**