Physics: Describing Motion

• Physics is the study of general science

Mechanics

• Motion is defined as the change in position with respect to a reference point.

Physical Quantities Describing Motion

• Distance refers to the length of a path covered by an object moving from an initial to a final position and is a scalar quantity.
• Displacement measures how far an object has moved in a specific direction from its original position and is a vector quantity.
• Speed indicates how fast something is moving, a scalar quantity.
• Instantaneous speed is the speed at a specific moment (e.g., speedometer reading).
• Average speed is the total distance traveled divided by the total time of travel.
• Velocity is the rate of change in displacement of an object over a given time interval and is a vector quantity.
• Acceleration is the rate of change of velocity over time and is a vector quantity.

Uniform Motion

• An object in uniform motion has constant speed and velocity, resulting in zero acceleration.
• A moving object will cover the same distance in equal time intervals.
• The net force acting on the object is zero.
• Velocity equals distance divided by time: v = d/t.

Accelerated Motion

• Accelerated motion happens when a moving object changes its velocity.
• Velocity can be altered by: changing speed, changing direction, or changing both speed and direction.

Uniformly Accelerated Motion

• Free fall occurs when an object moves solely under the influence of gravity.
• Acceleration due to gravity is constant at 9.8 m/s².
• Velocity in uniformly accelerated motion equals gravity times time: v = gt.

Useful Equations for Acceleration

• Acceleration = change in velocity / time taken
• Acceleration = (final velocity - initial velocity) / time taken
• Abbreviated: a = (Vf - Vi) / t

Force

• Force is an interaction that causes objects to change motion.
• Balanced forces are equal in magnitude and opposite in direction, resulting in a net force of zero.
• Unbalanced forces are not equal resulting in a net force.

Newton's Laws of Motion

Law of Inertia

• An object at rest stays at rest, and an object in motion stays in motion with constant velocity unless acted upon by an external force.

Law of Acceleration

• Applying enough force causes an object to accelerate.
• An object's acceleration is directly proportional to the net force and inversely proportional to its mass.
• Expressed mathematically: F = ma, where F is force, m is mass, and a is acceleration.

Law of Interaction

• For every action, there is an equal and opposite reaction.
• When one object exerts a force on another, the second object exerts an equal force in the opposite direction on the first object.

Newton's Law of Universal Gravitation

• Every particle in the universe attracts every other particle with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
• F = Gm₁m₂ / r²
  • F = Force
  • G = Gravitational constant
  • m₁ = Mass of object 1
  • m₂ = Mass of object 2
  • r = Distance
• The Gravitational constant G = 6.67 x 10⁻¹¹ Nm²/kg².

Energy

• Energy is the capacity of an object to do work.

Potential Energy

• Potential energy is stored energy, object at rest.
• PE = mgh, where PE = mass x gravity x height.

Kinetic Energy

• Kinetic energy is energy of motion; object in motion.
• KE = (1/2)mv², where KE = 1/2 mass x (velocity)².

Law of Conservation of Energy

• The total energy of an isolated system remains constant.
• Energy can neither be created nor destroyed, but transformed from one form to another.

Work

• Work is done when a force causes a displacement of an object.
• Work occurs when a force applied to an object causes it to move in the direction of the force.
• No work occurs when a force is applied without causing displacement or when the displacement is perpendicular to the force.
• Mathmatically, work is W = Fd where Work = Force x distance

Heat and Temperature

Temperature

• Temperature is a measure of the average kinetic energy of the molecules in a substance; higher temperature means greater molecular motion.

Temperature Scales

• Fahrenheit (°F)
  • Freezing point: 32 °F
  • Boiling point: 212 °F
  • Absolute zero: -459.67 °F
  • Conversion formula: °C = (°F - 32) × 5/9
• Celsius (°C)
  • Freezing point: 0 °C
  • Boiling point: 100 °C
  • Absolute zero: 273.15 °C
  • Conversion formula: °F = (°C × 9/5) + 32
• Kelvin (K)
  • Freezing point: 273.15 K
  • Boiling point: 373.15 K
  • Absolute zero: 0 K
  • Conversion formula: K = °C + 273.15

Heat

• Heat is the measure of internal energy absorbed or transferred.
• Heating is the process of increasing internal energy.
• Cooling is the process of decreasing internal energy.

Heat Transfer

• Heat transfers from higher to lower temperature regions until thermal equilibrium.
• Conduction is heat transfer through direct contact.
• Convection is heat transfer through fluid movement.
• Radiation is heat transfer through electromagnetic waves.

Thermodynamics

• Thermodynamics is the study of heat and its transformation to work or mechanical energy.

First Law of Thermodynamics

• The First Law of Thermodynamics based on the conservation of energy; energy cannot be created nor destroyed, only transformed.
• When heat is added, it converts to other forms of energy.

Second Law of Thermodynamics

• The Second Law of Thermodynamics emphasizes the direction of heat flow.
• Heat naturally flows from a hot to a cold object.
• A heat engine is a device that absorbs heat and partially converts it to mechanical work.
• A heat pump transfers heat from a cooler area to a warmer area by using mechanical work, effectively reversing the natural direction of thermal energy flow, and are used in referigerators.

Electricity

• Conductors are materials that allow charges to flow through them.
• Insulators present significant resistance to the flow of charges.

Ohm's Law

• Ohm's Law is that electric current is directly proportional to voltage and inversely proportional to electrical resistance.
• Voltage (V) is the pressure that creates current flow in a circuit.
• Current (I) is the flow of electrons through a circuit.
• Resistance (R) is the opposition to current flow.

Ohm's Law Equations

• V = I * R (volts = amps times ohms)
• I = V / R (amps = volts divided by ohms)
• R = V / I (ohms = volts divided by amps)

Coulomb's Law

• Coulomb's Law describes the force between two point charges and is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them.
• F = ke (q1q2 / r²) where:
  • F is the magnitude of the force in Newtons
  • q1 is the magnitude of the first charge in coulombs
  • q2 is the magnitude of the second charge in coulombs
  • r is the distance between the charges in meters
  • ke is Coulomb's constant = 9.0 x 10⁹ Nm²/C²
• Like charges repel each other; unlike charges attract each other.

Waves and Optics

• Waves transfer energy through a medium/space via oscillations or vibrations.

Longitudinal Waves

• Longitudinal wave vibrates parallel to the direction of propagation (back-and-forth motion).

Transverse Waves

• Transverse waves vibrate perpendicular to the direction of propagation (up and down motion).

Properties of Waves

• Wavelength (λ) is the distance between two consecutive points in phase on a wave measured in meters (m).
• Amplitude (A) is the maximum displacement of a wave from its rest position.
• Frequency (f) is the number of complete wave cycles passing a point per second = hertz (Hz).
• 1 Hz = 1 cycle per second.
• Period (T) the time is taken for one complete wave cycle to pass a given point; measured in seconds (s) = T=1/f.
• Wave speed describes the speed and direction of the wave motion.
• Useful equation: wave speed = wavelength (λ) x frequency (f).

Electromagnetic Spectrum

• Radio wave
• Microwave
• Infrared
• Visible light
• Ultraviolet
• X-ray
• Gamma ray

Properties of Light

• Reflection is the bouncing back of light when it strikes a surface.
  • Regular reflection occurs when light strikes a smooth, flat and shiny surface, reflects in one direction.
  • Diffuse reflection light reflects from a rough/uneven surface and scatters in many different directions.
• Refraction is the bending of light as it passes through a different medium, which is caused by a change in its speed.
• Dispersion is the separation of white light into rainbow colors after passing through a prism.
• Interference occurs when two or more light waves overlap, producing constructive and destructive interference patterns. constructive interference occurs Constructive interference occurs when adding waves that are in in phase increases the amplitude.
• Destructive interference occurs when adding waves that are out of phase reduces or cancels out the amplitude.
• Diffraction is the bending/spreading of waves around obstacles or narrow openings.
• Polarization restricts light vibrations to a plane perpendicular to propagation.
  • Unpolarized light consists of transverse waves vibrating in all directions.
  • Polarized light vibrates in one direction.

Mirrors

• Mirrors are reflecting surfaces that create images.
• Plane mirrors have a flat reflecting surface, creating virtual, upright images of the same size.
• Concave mirrors are spherical with an inward-curving reflective surface, which produces real/virtual, inverted/upright images of varying sizes.
• Convex Mirror is a spherical mirror with an outward-curving reflective surface; always forms virtual, upright, and smaller images, regardless of the object's position.