# Physics Definitions

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## Forces and Motion - Linear Motion

Distance
Distance is defined as the total path traveled by an object from one point to the other.

Displacement
Displacement is defined as the shortest distance between two point in a specific direction.

Speed
Speed is defined as the rate of change of distance.

Velocity
Velocity is defined as the rate of change of displacement.

Acceleration
Acceleration is defined as the rate of change of velocity.

Deceleration
Deceleration is the rate of decrease of velocity or how fast a velocity of a moving object decreases.

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## Forces and Motion - Inertia and Momentum

Inertia
Inertia is the tendency of an object resist to change its motion state. An object at rest will tend to remain at rest, or if moving will tend to continue its motion in a straight line.

Momentum
The momentum of an object is the product of the mass and the velocity of the object.

Law of Conservation Of Momentum
In a reaction between objects (collision or explosion), the total momentum before the reaction is equal to the total momentum after the reaction, provided that no external force acts on the system.

Elastic Collision
Elastic collision is the collision where the kinetic energy is conserved after the collision.

Inelastic Collision
Inelastic collision is the collision where the kinetic energy is not conserved after the collision.

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## Forces and Motion - Effects of Force

Newton’s First Law
In the absence of external forces, an object at rest remains at rest and an object in motion continues in motion with a constant velocity (that is, with a constant speed in a straight line).

Newton’s Second Law
The rate of change of momentum of a body is directly proportional to the resultant force acting on the body and is in the same direction.

Newton’s Third Law
Newton's third law of motion states that for every force, there is a reaction force with the same magnitude but in the opposite direction.

Friction
Friction is a force opposing motion.
How the crumble zone of a car can reduce injuries to passenger?

Friction Compensated Runway
A friction compensated run way is a runway which the friction of an object placed on it is balanced by the weight of the object itself.

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## Forces and Motion - Impulse and Impulsive Force

Impulse
Impulse is defined as the product of a force F acting on an object for a time, t.

Impulsive Force
Impulsive force is a force which acts on an object for a very short interval during a collision or explosion. It is equals to the change in momentum per unit time.

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## Forces and Motion - Gravity

Mass
Mass is defined as quantity of matter. The S.I. unit of mass is kg.

Weight
Weight of an object is the gravitational force acting on the object.

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## Forces and Motion - Forces in Equilibrium

Equilirium of Force
Forces acting on an object are in equilibrium if the net force acting on the object is zero. (Stationary or moving at unifrom velocity)

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## Forces and Motion - Work, Power and Efficiency

Work
Work done by a constant force is given by the product of the force and the distance moved in the direction of the force.

Energy
Energy is capacity to do work.

Power
Power is the rate of work done or the rate of energy conversion.

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## Forces and Motion - Elasticity

Elasticity

Elasticity is the property of a material to return to its original shape and size after force exerted is removed.

Spring Constant

Spring/force constant is the force required to extend the spring by one unit of extension.

Hooke’s Law

Hooke's law states that the extension of a spring is directly proportional to the applied force provided the elastic limit is not exceeded.

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