Physics: Physical Quantities

• Physics is a natural science that studies matter, its motion, and behavior through space and time, and that studies the related entities of energy and force.

Physical Quantities

• A physical quantity is a quantity that can be measured.
• Physical quantities are typically expressed as a numerical value multiplied by a unit.
• Base quantities are a set of fundamental physical quantities from which all other physical quantities can be derived.
• Examples of base quantities include length, mass, time, electric current, temperature, amount of substance, and luminous intensity.
• Derived quantities are physical quantities that are defined in terms of base quantities.
• Examples of derived quantities include area, volume, density, speed, force, energy, and power.
• Scalar quantities are physical quantities that have magnitude only.
• Examples of scalar quantities include mass, time, temperature, and speed.
• Vector quantities are physical quantities that have both magnitude and direction.
• Examples of vector quantities include displacement, velocity, acceleration, force, and momentum.

Measurement Techniques

• Measurement is the process of determining the magnitude of a physical quantity.
• Accuracy refers to how close a measurement is to the true value of the quantity being measured.
• Precision refers to the repeatability or reproducibility of a measurement.
• Errors in measurement can be classified as systematic errors or random errors.
• Systematic errors are consistent errors that occur in the same direction each time a measurement is made.
• Random errors are unpredictable errors that occur due to chance variations in the measurement process.
• Parallax error occurs when the observer's eye is not properly aligned with the measurement scale, leading to an inaccurate reading.
• To minimize parallax error, the observer should position their eye directly in line with the scale.
• Significant figures are the digits in a number that are known with certainty plus one uncertain digit.
• When performing calculations with measured values, the result should be rounded to the same number of significant figures as the least precise measurement.

Density

• Density is a measure of how much mass is contained in a given volume.
• Density is defined as mass per unit volume.
• The formula for density is: density = mass / volume or ρ = m / V.
• The SI unit of density is kilograms per cubic meter (kg/m³).
• Density can also be expressed in grams per cubic centimeter (g/cm³).
• To convert g/cm³ to kg/m³, multiply by 1000.
• Density is an intrinsic property of a substance, meaning it does not depend on the amount of substance present.
• Density is affected by temperature and pressure.
• When temperature increases, volume usually increases, which decreases density (for most substances).
• Higher pressure typically increases density.
• Objects with lower density will float on top of objects with higher density.

Mass and Weight

• Mass is a measure of the amount of matter in an object.
• Weight is the force of gravity acting on an object.
• The SI unit of mass is the kilogram (kg).
• The SI unit of weight is the Newton (N).
• Mass is a scalar quantity, while weight is a vector quantity.
• Mass is constant, regardless of location.
• Weight varies depending on the gravitational field strength.
• The relationship between mass and weight is given by the equation: weight = mass × gravitational acceleration (W = mg).
• Gravitational acceleration (g) on Earth is approximately 9.8 m/s².
• An object's weight can change depending on the gravitational field, but the mass remains constant.

Forces

• A force is an interaction that, when unopposed, will change the motion of an object.
• Force is a vector quantity, having both magnitude and direction.
• The SI unit of force is the Newton (N).
• Forces can cause objects to start moving, stop moving, change direction, or change shape.
• Contact forces are forces that require physical contact between objects.
• Examples of contact forces include friction, tension, normal force, and applied force.
• Non-contact forces are forces that act at a distance, without physical contact.
• Examples of non-contact forces include gravitational force, electric force, and magnetic force.
• Newton's First Law of Motion (Law of Inertia) states that an object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by a net external force.
• Inertia is the tendency of an object to resist changes in its state of motion.
• Newton's Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on the object, is in the same direction as the net force, and is inversely proportional to the mass of the object (F = ma).
• Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction.
• Free-body diagrams are used to represent the forces acting on an object.
• Tension is the pulling force exerted by a string, rope, cable, or similar object.
• Friction is a force that opposes motion between surfaces in contact.
• The normal force is the force exerted by a surface on an object in contact with it, perpendicular to the surface.

Motion

• Motion is the change in position of an object with respect to time.
• Displacement is the change in position of an object. It is a vector quantity.
• Distance is the total length of the path traveled by an object. It is a scalar quantity.
• Speed is the rate at which an object is moving. It is a scalar quantity.
• Velocity is the rate at which an object is changing its position. It is a vector quantity.
• Average speed is the total distance traveled divided by the total time taken.
• Average velocity is the displacement divided by the total time taken.
• Instantaneous speed is the speed of an object at a particular instant in time.
• Instantaneous velocity is the velocity of an object at a particular instant in time.
• Acceleration is the rate of change of velocity. It is a vector quantity.
• Uniform motion is motion with constant velocity (zero acceleration).
• Uniformly accelerated motion is motion with constant acceleration.
• The equations of motion for uniformly accelerated motion are:
  • v = u + at, where v is the final velocity, u is the initial velocity, a is the acceleration, and t is the time.
  • s = ut + (1/2)at², where s is the displacement.
  • v² = u² + 2as
• Projectile motion is the motion of an object thrown or projected into the air, subject to only the acceleration of gravity.
• Air resistance is a force that opposes the motion of an object through the air.
• Terminal velocity is the constant speed that a freely falling object eventually reaches when the force of air resistance equals the force of gravity.
• Circular motion is the motion of an object along a circular path.
• Angular velocity is the rate at which an object is rotating or revolving.
• Centripetal force is the force that is required to keep an object moving in a circular path.
• Momentum is a measure of the mass in motion.
• Momentum is calculated as mass multiplied by velocity (p = mv).
• The principle of conservation of momentum states that the total momentum of a closed system remains constant if no external forces act on it.