Physics Keypoints; Motion; Motion can be defined as the change in position of an object with respect to its surroundings over time. It is the movement of an object from one place to another.
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Physics Keypoints; Motion
(a) Types of Motion
Motion can be classified into different types:
- Translational Motion: when an object moves in a straight line.
- Rotational Motion: when an object rotates around an axis.
- Oscillatory Motion: when an object moves back and forth repeatedly.
- Random Motion: when an object moves in a random manner without any fixed path.
- Spin Motion: when an object rotates around its own axis.
(b) Relative Motion
Relative motion refers to the motion of an object in relation to another object. It is important to note that motion is always relative, and objects are always in motion in relation to something else.
(c) Causes of Motion
Motion is caused by the application of force on an object. Force can be defined as a push or pull that changes or tends to change the state of motion of an object.
(d) Types of Force
Forces can be classified into two types:
(i) Contact Force: a force that is applied through physical contact.
(ii) Force Field: a force that is applied without physical contacts, such as gravitational force.
(e) Linear Motion
The linear motion refers to the motion of an object in a straight line. Important concepts of linear motion include:
(i) Speed, Velocity, and Acceleration: Speed is the rate at which an object moves. Velocity is the rate at which an object moves in a specific direction. Acceleration is the rate at which an object changes its velocity.
(ii) Equations of Uniformly Accelerated Motion: These equations are used to calculate the motion of an object with constant acceleration.
(iii) Motion under Gravity: Motion under gravity refers to the motion of an object when it is affected by the force of gravity. The acceleration due to gravity is 9.81 m/s^2.
(iv) Distance-time graph and Velocity-time graph: These graphs are used to visualize the motion of an object and its velocity over time.
(v) Instantaneous Velocity and Acceleration: These are the velocity and acceleration of an object at a specific instant in time.
(f) Projectiles:
(i) Calculation of range, maximum height, and time of flight from the ground and height:
Projectiles are objects that are launched into the air and then move under the influence of gravity alone. Examples of projectiles include cannonballs, arrows, and even a thrown ball. The motion of a projectile can be broken down into two components: horizontal motion and vertical motion. Horizontal motion is constant and is not affected by gravity. Vertical motion is affected by gravity, which causes the projectile to follow a curved path.
To calculate the range of a projectile, we need to know the initial velocity, angle of projection, and gravitational acceleration. The range of a projectile is the distance covered by it on the horizontal plane before hitting the ground.
The maximum height attained by a projectile can be calculated by using the equation:
h = (v₀² sin²θ)/(2g)
where h is the maximum height, v₀ is the initial velocity, θ is the angle of projection, and g is the gravitational acceleration.
The time of flight is the total time taken by the projectile to hit the ground. It can be calculated using the equation:
t = 2v₀ sinθ/g
where t is the time of flight.
(ii) Applications of Projectile Motion:
Projectile motion has numerous applications in real life. It is used in sports like basketball, volleyball, and cricket, where players use projectile motion to hit the ball or throw it toward a target. Projectile motion is also used in the design of missiles, rockets, and satellites. Understanding projectile motion is important for understanding how objects move through the air and can be used to design more efficient and accurate systems.
(g) Newton’s laws of motion:
(i) Inertia, mass, and force:
Newton’s laws of motion are three fundamental laws that describe the relationship between a body and the forces acting upon it. The first law of motion states that a body at rest will remain at rest, and a body in motion will continue to move with a constant velocity unless acted upon by an external force. This property of matter is called inertia.
The second law of motion states that the acceleration of an object is directly proportional to the force applied and inversely proportional to the mass of the object. This law can be expressed mathematically as F = ma, where F is the force, m is the mass of the object, and a is the acceleration.
(ii) Relationship between mass and acceleration:
The second law of motion states that the acceleration of an object is directly proportional to the force applied and inversely proportional to the mass of the object. This means that the greater the mass of an object, the more force is required to accelerate it to a given speed. On the other hand, a smaller mass requires less force to achieve the same acceleration.
(iii) Impulse and momentum:
The third law of motion states that for every action, there is an equal and opposite reaction. When a force is applied to an object, it will accelerate, and its momentum will change. The change in momentum of an object is directly proportional to the force applied and the time for which it is applied. This relationship is expressed as:
J = Ft
where J is the impulse, F is the force, and t is the time for which the force is applied.
(iv) Force–time graph:
A force-time graph is a graphical representation of the force applied to an object over a period of time. The area under the curve of the graph represents the impulse applied to the object. The slope of the graph represents the rate at which the force is changing, which is equivalent to the acceleration of the object.
(v) Conservation of linear momentum:
The conservation of linear momentum is a fundamental principle of physics. It states that the total momentum of a system remains
(h) Motion in a Circle:
When an object moves in a circular path, it is said to be in a circular motion. The motion of an object in a circle is described in terms of its angular velocity and angular acceleration.
(i) Angular Velocity and Angular Acceleration: Angular velocity is the rate of change of angular displacement with respect to time. It is measured in radians per second (rad/s). Angular acceleration is the rate of change of angular velocity with respect to time. It is measured in radians per second squared (rad/s^2).
(ii) Centripetal and Centrifugal Forces: Centripetal force is the force that keeps an object moving in a circular path. It always points towards the center of the circle. Centrifugal force is the apparent force that seems to push an object away from the center of the circle. It is a reaction force to the centripetal force and does not actually exist.
(iii) Applications: The motion in a circle has many practical applications, such as the motion of planets around the sun, the motion of electrons around the nucleus, the motion of a car around a bend, etc.
(i) Simple Harmonic Motion (S.H.M): Simple harmonic motion is a type of periodic motion where the restoring force is directly proportional to the displacement of the object from its equilibrium position.
(i) Definition and Explanation of Simple Harmonic Motion: Simple harmonic motion is a type of motion where an object oscillates back and forth about its equilibrium position. The motion is said to be harmonic because the motion follows a sinusoidal curve.
(ii) Examples of Systems that Execute S.H.M: Some examples of systems that execute S.H.M are a simple pendulum, a mass-spring system, a tuning fork, etc.
(iii) Period, Frequency, and Amplitude of S.H.M: Period is the time taken for one complete oscillation. It is denoted by T and is measured in seconds (s). Frequency is the number of oscillations per unit of time. It is denoted by f and is measured in Hertz (Hz). Amplitude is the maximum displacement of the object from its equilibrium position.
(iv) Velocity and Acceleration of S.H.M: The velocity and acceleration of an object executing S.H.M can be found by differentiating the displacement equation. The velocity is maximum at the equilibrium position and is zero at the ends of the oscillation. The acceleration is maximum at the ends of the oscillation and is zero at the equilibrium position.
(v) Simple Treatment of Energy Change in S.H.M: The total mechanical energy of an object executing S.H.M remains constant throughout the motion. At the equilibrium position, all the energy is in the form of potential energy, while at the ends of the oscillation, all the energy is in the form of kinetic energy.
(vi) Force Vibration and Resonance (Simple Treatment): Forced vibration is the motion of an object that is subjected to an external force. Resonance occurs when the frequency of the external force matches the natural frequency of the system. This causes the amplitude of the oscillation to increase significantly. Resonance can be useful in many applications, such as tuning a musical instrument. However, it can also be dangerous, such as when a bridge collapses due to resonance caused by strong winds.
