Summary
Highlights
Every measurement or quantity has a unit. For very large or small numbers, prefixes like kilo or micro are used. Converting units requires understanding if a larger or smaller number is needed, multiplying or dividing by the conversion factor accordingly. Standard form (e.g., 5 * 10^-6) is used for very small or large numbers.
Forces are pushes or pulls and can be contact (friction, tension) or non-contact (magnetism, gravity). Forces are represented by vectors, showing both direction and magnitude. The resultant force is the sum of all forces on an object. Balanced forces result in no acceleration, while unbalanced forces lead to acceleration (Newton's Second Law: F=ma). Scalars have magnitude only, while vectors have both magnitude and direction. Weight is the force due to gravity (mass * gravitational field strength).
Speed and velocity are measured in meters/second, with velocity also including direction. Distance-time graphs show speed as the gradient, while velocity-time graphs show acceleration as the gradient. The area under a velocity-time graph represents distance traveled. Newton's equations of motion (SUVAT) predict an object's behavior under constant acceleration.
Newton's First Law states that an object's motion is constant if no resultant force acts on it (inertia). Newton's Second Law (F=ma) describes motion under unbalanced forces. Newton's Third Law states that for every action, there is an equal and opposite reaction force, acting on different objects. Car stopping distance comprises thinking distance and braking distance, both affected by speed and other factors like distractions or road conditions.
Momentum (mass * velocity) measures how difficult it is to stop an object. It's a vector quantity. In collisions, total momentum is always conserved, even if kinetic energy is not. Newton's Second Law can also be expressed as force equals the rate of change of momentum, explaining the effectiveness of safety features like seatbelts and airbags.
Energy is an abstract concept that describes interactions within a system; it is conserved, meaning it cannot be created or destroyed. Energy exists in various 'stores': kinetic (1/2 mv^2), gravitational potential (mgh), elastic potential (1/2 kx^2), and thermal (mcΔT). Energy is transferred between these stores or objects. In a closed system, energy is conserved, allowing calculations where one energy type converts to another.
Energy sources are how we obtain energy. Finite (non-renewable) sources include fossil fuels and nuclear fuel. Renewable sources include wind, hydroelectric, solar, geothermal, and biofuel. Each source has its method of generating power, usually for electricity.
All waves transfer energy without transferring matter. Longitudinal waves (sound, seismic P-waves) have oscillations parallel to energy transfer. Transverse waves (water waves, seismic S-waves, light) have oscillations perpendicular to energy transfer. Key wave properties include amplitude, wavelength (lambda), time period (T), and frequency (f). The wave equation is V = f * lambda, and frequency is the reciprocal of the time period.
Sound waves cause ear drums to vibrate, sending signals to the brain. Humans hear frequencies between 20 Hz and 20 kHz; above this is ultrasound. Ultrasound is used for imaging inside bodies (e.g., baby scans) and for sonar due to its reflection properties at material boundaries.
Specular reflection occurs from smooth surfaces, where the angle of incidence equals the angle of reflection. Diffuse reflection happens on rough surfaces. Refraction is the change in direction of waves as they pass from one medium to another, due to a change in speed. When light slows down, it bends closer to the normal. Total internal reflection occurs when the angle of incidence exceeds the critical angle, a principle used in fiber optics for high-speed data transfer.
Electromagnetic (EM) waves are unique as they travel through a vacuum, unlike other waves. The EM spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. EM waves are produced when electrons lose energy (except gamma rays, from nuclei). Higher frequency means more energy and a shorter wavelength. UV, X-rays, and gamma rays are ionizing and can damage cells, leading to cancer. EM waves have diverse uses in communication, heating, imaging, and medicine.
Lenses use refraction to converge (convex) or diverge (concave) light rays. A convex lens can form real, inverted, and diminished images or virtual, upright, and magnified images depending on object distance. Concave lenses always produce virtual, diminished, and upright images. Magnification is the ratio of image height to object height. Color perception depends on wavelengths of light absorbed and reflected by objects and detected by the retina. A black body absorbs and emits all wavelengths of radiation, influencing an object's temperature.
The modern atomic model evolved through discoveries by J.J. Thompson (plum pudding model), Ernest Rutherford (small, positive nucleus), Niels Bohr (electron shells), and James Chadwick (neutrons). Atoms consist of protons (positive), neutrons (neutral), and electrons (negative). The atomic number defines the element, and the mass number is protons + neutrons. Isotopes are atoms of the same element with different numbers of neutrons (different mass numbers).
Radiation refers to particles or waves emitted from an atom, including gamma waves from the nucleus. Ionizing radiation (gamma, UV, X-rays, alpha, beta) can knock electrons off atoms, damaging cells and causing cancer. Unstable nuclei undergo decay, emitting alpha (2 protons, 2 neutrons) or beta (an electron from a neutron decaying into a proton) particles. Decay equations balance atomic and mass numbers.
Alpha particles have high ionizing ability but low penetrating power (stopped by air/paper). Beta particles have moderate ionizing and penetrating power (stopped by aluminum). Gamma rays have low ionizing ability but very high penetrating power (reduced by lead/concrete). Background radiation comes from natural and man-made sources. Activity (radioactivity) is the decay rate, measured in Becquerel (Bq). Half-life is the time for activity (or number of unstable nuclei) to halve.
Nuclear fission is when a neutron is absorbed by a large nucleus (e.g., Uranium-235), causing it to split into two smaller nuclei, releasing energy and more neutrons, leading to a chain reaction. This controlled reaction generates electricity in nuclear reactors. Nuclear fusion, occurring in stars, involves two light nuclei fusing to form a heavier one, releasing immense energy. Fusion reactors are still under development due to engineering challenges.
In a nuclear reactor, fuel rods contain fissionable material. A moderator (water, graphite) slows down released neutrons to 'thermal speeds' for further fission. Control rods (boron) absorb neutrons to regulate the reaction rate. Nuclear waste is radioactive and hot, requiring safe, long-term disposal in vitrified form deep underground.
Our solar system includes the sun, eight planets, and an asteroid belt. Natural satellites (moons) orbit planets. Stars form from nebulae (clouds of dust and gas) collapsing under gravity, initiating fusion. A star remains stable in its 'main sequence' if fusion pressure balances gravity. Stars evolve into red giants (then white/black dwarfs) or super red giants (then supernovae, forming neutron stars or black holes).
Artificial satellites orbit Earth. Geostationary satellites maintain a constant position above the equator with a 24-hour orbit, used for communication. Satellites in circular motion experience a centripetal force towards the center. Other satellites use elliptical orbits for reconnaissance or GPS. Redshift of light from distant galaxies indicates they are moving away from us, with more distant galaxies receding faster. This is evidence for the Big Bang Theory and an expanding universe, supported by cosmic microwave background radiation (CMBR) – faint microwave radiation detected from all directions.