Physics - Motion

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Motion

A body is said to be in motion, if it changes its position wrt time and frame of reference.

Motion is a relative term. Raman is in state of rest wrt his friend sitting next to him on Merry-Go-Round. He is simultaneously in a state of motion wrt his mother waiting on the ground.

Types of Motion

1. Rectilinear Motion: When an object moves along a straight path, it is said to be in rectilinear motion. For example, a car moving along a straight road.

2. Circular Motion: When an object moves in a circular path, it is in circular motion. For example, a spinning top.

3. Periodic Motion: Motion that repeats itself at regular intervals is called periodic motion. For example, the motion of a pendulum.

4. Rotational Motion: This occurs when an object spins about an axis. For example, the rotation of the Earth on its axis.

5. Oscillatory Motion: Oscillatory motion is back-and-forth motion around a central point. For example, a swinging pendulum.

Scalar and Vector Quantities

• Scalar: They are the physical quantities that have only magnitude, but no direction. For example, length, speed, etc.
• Vector: These physical quantities have both magnitude as well as direction. For example, displacement, velocity, acceleration, etc.

Distance and Displacement

• Distance: It is the length of the actual path covered by an object. Distance is a scalar quantity and is always positive.
• Displacement: It is the shortest distance between the initial and final position of an object in a particular direction. Displacement is a vector quantity and can be positive, negative, or zero.

Speed and Velocity

• Speed: Speed is the rate of change of distance with respect to time. It is a scalar quantity and is always positive.
• Speed = distance/time
• Average Speed = Total distance / total time
• Velocity: Velocity is the rate of change of displacement with respect to time. It is a vector quantity and can be positive, negative, or zero.
• Acceleration = (Final velocity - Initial Velocity)/ time

Equations of Motion

1. First Equation of Motion: $�=�+��$

   • $�$ = final velocity
   • $�$ = initial velocity
   • $�$ = acceleration
   • $�$ = time taken

2. Second Equation of Motion: $�=��+\frac{1}{2}�{�}^2$

   • $�$ = displacement
   • $�$ = initial velocity
   • $�$ = acceleration
   • $�$ = time taken

3. Third Equation of Motion: ${�}^2={�}^2+2��$

   • $�$ = final velocity
   • $�$ = initial velocity
   • $�$ = acceleration
   • $�$ = displacement

Acceleration

Acceleration is the rate of change of velocity with respect to time. It can be positive (when an object is speeding up), negative (when an object is slowing down), or zero (when an object is moving at a constant velocity).

Graphical Representation of Motion

Graphs, such as distance-time graphs and velocity-time graphs, are useful tools for representing and analyzing motion.

• A straight line on a distance-time graph represents uniform motion.
• The slope of a distance-time graph gives the speed of the object.
• A horizontal line on a velocity-time graph indicates constant velocity.
• The area under a velocity-time graph represents the displacement of the object.

Newton's Laws of Motion

1. Newton's First Law of Motion (Law of Inertia): An object at rest tends to stay at rest, and an object in motion tends to stay in motion with the same speed and in the same direction unless an external force acts on it.

2. Newton's Second Law of Motion: The force acting on an object is equal to the product of the mass of the object with its acceleration. $�=��$

3. Newton's Third Law of Motion (Action-Reaction): For every action, there is an equal and opposite reaction.

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