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# Physics Keypoints; Scalars and Vectors

Posted by on March 22, 2023 0 Physics Keypoints; Scalars and Vectors; Scalars and vectors are two types of physical quantities used to describe the properties of objects and their motion. In this topic, we will discuss the differences between scalar and vector quantities, provide examples of each, and explore how to resolve vectors in two perpendicular directions. ### (i) Definition of Scalar and Vector Quantities:

A scalar quantity is a physical quantity that has only magnitude, or size, and no direction. Examples of scalar quantities include temperature, mass, time, distance, speed, and energy.

A vector quantity, on the other hand, has both magnitude and direction. Examples of vector quantities include displacement, velocity, acceleration, force, and momentum.

### (ii) Examples of Scalar and Vector Quantities:

Some examples of scalar quantities are:

• Mass of an object
• The temperature of an object
• Time
• Distance
• Speed
• Volume

Some examples of vector quantities are:

• Displacement of an object
• The velocity of an object
• Acceleration of an object
• Force acting on an object
• The momentum of an object

### (iii) Relative Velocity:

Relative velocity is the velocity of an object with respect to another moving object. It is calculated by subtracting the velocity of one object from the velocity of the other. For example, if a car is traveling at 60 km/h and a person is walking at 5 km/h in the same direction, then the relative velocity of the person with respect to the car is 55 km/h.

### (iv) Resolution of Vectors into Two Perpendicular Directions:

The resolution of vectors is the process of breaking down a single vector into two perpendicular components. This is done to simplify the vector’s direction and magnitude and is often used in physics and engineering to analyze motion.

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There are two methods for resolving vectors into two perpendicular directions: graphical and algebraic.

Graphical method: In the graphical method, a vector is drawn to scale and then resolved into two perpendicular components using a ruler and protractor. The components can then be calculated using trigonometry.

Algebraic method: In the algebraic method, the vector is expressed as the sum of two perpendicular components, and the components can be calculated using basic algebraic equations.

Overall, understanding scalar and vector quantities, as well as how to resolve vectors, is crucial for understanding many concepts in physics and engineering.

## Keypoints

Scalars and vectors are two types of physical quantities used in physics to describe different aspects of an object’s motion. Scalars have only magnitude, whereas vectors have both magnitude and direction.

Examples of scalar quantities include distance, speed, time, and temperature. These quantities are described only by their magnitude, without any direction. In contrast, examples of vector quantities include displacement, velocity, acceleration, force, and momentum. These quantities are described by both their magnitude and direction.

To determine the resultant of two or more vectors, we use vector addition. The magnitude and direction of the resultant vector are calculated by adding the magnitudes and directions of the individual vectors. The graphical method of vector addition involves drawing the vectors to scale, placing them head to tail, and drawing the resultant vector from the tail of the first vector to the head of the last vector.

Relative velocity is the velocity of one object as observed from the perspective of another object that is also in motion. To calculate relative velocity, we use vector subtraction. The relative velocity vector is the difference between the velocity vectors of the two objects.

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When a vector is given, we can resolve it into two perpendicular components. These components are called the x and y components. The x-component is the magnitude of the vector projected onto the x-axis, and the y-component is the magnitude of the vector projected onto the y-axis. The Pythagorean theorem can be used to find the magnitude of the vector, and the tangent function can be used to find the angle that the vector makes with the x-axis.

The graphical method of vector resolution involves drawing the vector to scale and constructing a right triangle with the vector as the hypotenuse. The x-component is the adjacent side of the triangle, and the y-component is the opposite side of the triangle. The magnitudes and directions of the components can be found using trigonometry.

In conclusion, understanding the difference between scalar and vector quantities, how to determine the resultant of vectors, how to calculate relative velocity, and how to resolve vectors into two perpendicular components is crucial for success in physics.

Here are some of the commonly used formulas:

1. Magnitude of a vector: |a| = sqrt(a1^2 + a2^2 + a3^2)
2. Vector addition: a + b = (a1 + b1)i + (a2 + b2)j + (a3 + b3)k
3. Vector subtraction: a – b = (a1 – b1)i + (a2 – b2)j + (a3 – b3)k
4. Dot product: a · b = a1b1 + a2b2 + a3b3
5. Cross product: a x b = (a2b3 – a3b2)i – (a1b3 – a3b1)j + (a1b2 – a2b1)k
6. Magnitude of the cross product: |a x b| = |a| |b| sin θ
7. Resolution of a vector: a = a1 + a2
8. Relative velocity: vAB = vA – vB
9. Law of cosines: c^2 = a^2 + b^2 – 2ab cos C
10. Law of sines: a/sin A = b/sin B = c/sin C

These formulas can be used to solve various problems related to scalars and vectors. 