# Motion

## ðŸ‘‰Â All Chapter ContentsÂ ðŸ‘ˆÂ

• 2.1 Rest and Motion
• 2.2 Different Types of Motion
• 2.3 Scalar and Vector quantities
• 2.4 Distance and Displacement
• 2.5 Speed and Velocity
• 2.6 Acceleration and Deceleration or Retardation
• 2.7 Equation of Motion
• 2.8 Laws of Falling Bodies

What is scalar quantity?

Physical quantities which can be fully expressed by magnitude only are called scalar quantities Length, mass, speed, work, energy, time, temperature, etc. are the examples of scalar quantities.

What is vector quantities?

Physical quantities which need both magnitude and direction to be fully expressed are called vector quantities. Displacement, velocity, acceleration, force, electric intensity, etc. are the examples of vector quantity.

What is the unit of displacement?

SI unit of displacement is meter (m).

What is speed?

The quantity by which we can measure how fast a body moves or distance travelled, is called speed.

What is the unit of speed?

The SI unit of speed is meter/second (ms-1).

What is the dimension of speed?

The dimension of speed is, [v] = [LT-1].

What is negative acceleration / retardation?

The rate of decrease of velocity of a body with time is called negative acceleration / retardation.

What is the dimension of acceleration?

The dimension of acceleration is [a] = [LT-2]

The is the nature of velocity-time graph in the case of uniform acceleration?

In the case of uniform acceleration velocity - time graph is a straight line.

What is the dimension of acceleration due toÂ  gravity?

The dimension of acceleration due to gravity is [g] = [LT-2]

In which place of the earth the magnitude of g is considered as standard?

The value of g at sea level altitude 45 degree is accepted as the standard value.

What is called the attraction between earth and moon?

The attraction between earth and moon is known as gravity.

What is the standard value of acceleration due to gravity.

The standard value of acceleration due to gravity is 9.81 ms-2.

What kind of quantity of velocity? Explain.

The rate of change of position in time with its direction is called velocity. Velocity is a vector quantity. Velocity has both magnitude and direction which means it needs both magnitude and direction to be fully expressed.

When will the velocity of a body become zero?

The rate of change of position in time with its direction is called velocity. If we put an external force on a body as long a there is force there will be displacement. when there is no displacement the velocity of body becomes zero.

What is the meaning of acceleration of a body is 5 ms-2 in the west direction?

The acceleration of a body 5 ms-2 in west means the velocity of the body increases 5 ms-1 per second in west direction. The direction of this increasement is west from initial position.

Can we say that acceleration due to gravity is uniform acceleration? If so, then why?

Acceleration due to gravity is uniform acceleration. The rate of increase of velocity of a freely falling body on earth due to force of gravity is called the acceleration due to gravity. From this definition it is clear that when a body falls its velocity increases with the same rate. So we can say that acceleration due to gravity is uniform acceleration.

What is the reason behind the attraction between earth and moon?

Every particle of this universe is attracted towards each other. The force of attraction between any two bodies or particles in this universe is called 'Gravitation'. If earth is one of the two bodies, then the force of attraction is called gravity. So the reason behind the attraction between moon and earth is force of gravity.

Force of gravitation is an attraction force. Explain it.

Force of gravitation is the attraction force between two bodies. Two charged bodies attract each other when the charges are opposite, which means one is positive and the other is negative. They repulse when the charges are same, which means either both are positive or both are negative. But force of gravitation is only force of attraction. Force of gravitation works in the direction of additional straight line of two bodies. It doesn't depend on the nature of the medium. No matter what is the medium there will be no change in force.

What is average velocity?

If a body does not move with uniform velocity, then the velocity obtained by dividing the total displacement by time is called average velocity.

In the universe every rest and speed is relative. No rest or motion is absolute. Explain it with example.

Actually whether an object is at rest or not depends on the reference object. If the reference frame is actually in rest, the object will be actually in rest with respect to that frame. This type of rest is called absolute rest. A body is said to be in absolutely rest when it is in rest respect to an absolutely rest object.

Similarly absolute motion of a body is its motion with respect to a reference object absolutely at rest. But in this universe it is not possible to get a reference object, which is at absolute rest. Since the earth is continuously moving round the sun, while the sun itself is moving along the galaxy with its planets and satellites. Thus when we say that a body is at rest or in motion, we mean it is to be so with respect to a body apparently at rest. So we can say that in this universe all rest and all motion are relative. No rest or no motion is absolute.

## 2.1 Rest and Motion

• What is rest?
• What is motion?
• What is a position?
• What is a reference point?
• What do you understand by reference frame?
• All the rests and motion of the universe are relative, no motion is absolute, no absolute rest - explain.

• What is linear motion?
• What is circular motion?
• What is translational motion?
• What is periodic motion?
• What is oscillatory motion?
• What is simple harmonic motion?
• Explain all oscillatory motions are periodic motions but all periodic motions are not oscillatory motions.

• What is quantity?
• What is the normal body temperature?
• What is a scalar quantity?
• What is a vector quantity?
• Write the difference between scalar quantities and vector quantities.
• Work is a scalar quantity - explain.
• Explain the intensity of electricity as a vector quantity.

• What is distance?
• What is displacement?
• The movement does not depend on the direction of the object - explain.
• What do you mean by the movement of an object is 60 m southward.

• What is speed?
• What is the unit of speed?
• What is the dimension of speed?
• What is average speed?
• What is instantaneous speed?
• What do you understand by the speed of a car is 45 km/h?
• What is velocity?
• What is the unit of velocity?
• What is the dimension of velocity?
• What is average velocity?
• What is uniform velocity?
• What is unequal velocity?
• When can the velocity of an object be zero?
• Write the difference between speed and velocity.

• What is acceleration?
• What is the unit of acceleration?
• What is the dimension of acceleration?
• What is uniform acceleration?
• What is unequal acceleration?
• Acceleration due to gravity is called uniform acceleration - explain.
• What is deceleration or retardation?
• Gravitational acceleration is called uniform acceleration - explain.

• Write all the equation of motion.
Mathematical Problems:

## 2.8 Laws of Falling Bodies

• What is gravity?
• What is gravitation?
• What is acceleration due to gravity?
• What is falling body?
• Write the laws of falling bodies.
• What is the first law of falling bodies? Explain.
• What is the second law of falling bodies? Explain.
• What is the third law of falling bodies? Explain.
Mathematical Problems: