Physics: Force and Pressure

• Physics is the branch of science studying nature and natural phenomena.
• Physics involves the study of matter, energy, and their interactions.

Force

• A force is a push or pull on an object from its interaction with another object.
• Forces initiate motion, halt movement, alter speed, or change direction.
• Forces also change an object's shape or size.
• Measured in Newtons (N).
• Force = mass × acceleration (F=ma)

Types of Forces

• Contact forces necessitate physical touching between objects.
  • Examples include frictional force, tension force, normal force, and applied force.
• Non-contact forces act between objects without physical contact.
  • Examples include gravitational force, electrostatic force, and magnetic force.

Pressure

• Pressure is force acting perpendicularly on a unit area of a surface.
• Pressure = Force / Area (P=F/A).
• Pascals (Pa) or N/m² are the units of measurement.
• Fluids (liquids and gases) exert pressure in all directions.

Friction

• Friction opposes motion between contacting surfaces.
• Friction turns kinetic energy into thermal energy (heat).
• Types of friction:
  • Static friction prevents an object from starting to move.
  • Sliding friction opposes an object sliding over a surface.
  • Rolling friction opposes an object rolling over a surface.
  • Fluid friction opposes an object through a fluid (liquid or gas).
• Factors influencing friction:
  • The nature of the surfaces.
  • The force pressing the surfaces together.
• Friction can be reduced by:
  • Using lubricants like oil or grease.
  • Using ball bearings or rollers.
  • Streamlining shapes moving through fluids.
• Friction can be increased by:
  • Increasing surface roughness.
  • Increasing the force pressing surfaces together.

Sound

• Sound is energy that produces a sensation of hearing.
• Sound is produced by vibrating objects.
• Sound travels as a wave through mediums like solids, liquids, or gases.
• Sound cannot travel through a vacuum.

Characteristics of Sound Waves

• Frequency: Vibrations per second, measured in Hertz (Hz).
  • Determines the pitch of sound (high or low).
• Amplitude: Maximum wave displacement from equilibrium.
  • Determines loudness or intensity.
• Wavelength: Distance between two consecutive crests or troughs.
• Time Period: The time for one complete oscillation

Speed of Sound

• Sound speed varies depending on the medium.
• Sound moves faster in solids than liquids, and faster in liquids than gases.
• Sound speed increases with temperature.
• Approximate sound speeds:
  • Air: 343 m/s
  • Water: 1480 m/s
  • Steel: 5960 m/s

Human Ear

• The human ear detects sound.
• Three main parts:
  • Outer ear collects sound waves.
  • Middle ear amplifies sound waves.
  • Inner ear converts sound waves into electrical signals for the brain.

Noise Pollution

• Noise pollution is excessive or unwanted sound, negatively impacting health and the environment.
• Sources:
  • Traffic, construction, industry, loudspeakers.
• Effects:
  • Hearing loss, stress, sleep disturbance, high blood pressure.
• Reduction measures:
  • Planting trees, noise barriers, source control.

Light

• Light is energy that enables sight.
• Light travels in a straight line.
• Light displays wave properties.

Reflection of Light

• Reflection is light bouncing back from a surface.
• Laws of reflection:
  • Incidence angle equals reflection angle.
  • Incident ray, reflected ray, and normal all lie in the same plane.
• Types of reflection:
  • Regular reflection: Light reflects from a smooth surface to form a clear image.
  • Irregular reflection (diffusion): Light reflects from a rough surface, scattering light in different directions.

Refraction of Light

• Refraction is light bending when it passes between media.
• Bending amount depends on refractive indices.
• Light bends toward the normal when moving from a rarer to a denser medium.
• Light bends away from the normal when moving from a denser to a rarer medium.

Dispersion of Light

• Dispersion is white light splitting into its colors (spectrum) through a prism.
• Spectrum colors: red, orange, yellow, green, blue, indigo, violet (ROYGBIV).

Human Eye

• The human eye detects light for sight.
• Main parts:
  • Cornea: Transparent outer layer that refracts light.
  • Iris: Controls light entering the eye.
  • Pupil: Opening in the iris.
  • Lens: Focuses light onto the retina.
  • Retina: Contains photoreceptor cells (rods and cones).
  • Optic nerve: Transmits signals to the brain.
• Rods are sensitive to dim light for black and white vision.
• Cones are sensitive to bright light for color vision.

Electric Charge

• Electric charge is a fundamental property that causes matter to experience force in an electromagnetic field.
• Two types: positive and negative.
• Like charges repel, unlike charges attract.
• The SI unit is the coulomb (C).

Electric Current

• Electric current is the rate of electric charge flow through a conductor.
• Current = Charge / Time (I=Q/t).
• Measured in Amperes (A).
• Conventional current flows from positive to negative.

Electric Circuits

• An electric circuit is a closed loop allowing electric current to flow.
• Basic components:
  • Source of electrical energy (e.g., battery).
  • Conducting wires.
  • Load (e.g., light bulb, resistor).
  • Switch.
• Types of circuits:
  • Series circuit: Components connected in a single path.
  • Parallel circuit: Components connected in multiple paths.

Effects of Electric Current

• Heating effect: Electric current through a resistor produces heat (e.g., electric heater).
• Magnetic effect: Electric current creates a magnetic field (e.g., electromagnet).
• Chemical effect: Electric current can cause chemical changes (e.g., electrolysis or electroplating).

Static Electricity

• Static electricity is electric charge accumulation on an object's surface.
• Often produced by friction.
• Examples: Lightning, balloon on hair.

Lightning

• Lightning is a large static electricity discharge between clouds or between a cloud and the ground.
• Dangerous, causing fires, injuries, or death.
• Lightning conductors protect buildings.

Some Natural Phenomena

• Earthquakes: Sudden energy release in the Earth's crust, creating seismic waves.
• Volcanoes: Ruptures in the Earth's crust where molten rock, hot ash, and gases escape the surface.
• Cyclones: Large air masses rotating around a low-pressure center.

Explanation of force as a push or pull affecting motion and object shape. Covers contact and non-contact forces like friction, gravity, and magnetism. Defines pressure as force per unit area, measured in Pascals.