paper 2 physics

• Force is any push or pull, contact forces occur when objects are physically touching like pushing a door, while non-contact forces include magnetism, electrostatic forces, and gravity
• Even contact forces are due to electrostatic repulsion between electrons, for example, pushing a door involves a normal contact force, other contact forces could be friction, air resistance, and tension
• Forces can be represented with vectors, arrows showing direction and magnitude, with the length of the arrow indicating the force's size
• If two forces act on an object, there's a resultant force found by adding the vectors, if they're in opposite directions, one must be negative, e.g., a resultant force of 3 Newtons to the right
• If vectors are at right angles, Pythagoras is used to find the resultant, trigonometry (SOHCAHTOA) can be used to find angles, especially tan for balanced forces adding up to zero, meaning no acceleration
• A scalar quantity has magnitude but no direction, e.g., displacement is distance traveled with a direction, while velocity is the vector form of speed
• Weight is the force due to gravity acting on an object, calculated by multiplying mass in kg by gravitational field strength (9.8 N/kg on Earth)
• Energy used to lift an object is calculated using the work done equation: work done = force × distance moved, which is also the equation for gravitational potential energy gained
• Deforming objects can be described by Hooke's Law: Force = spring constant × extension, where the spring constant is measured in N/m
• The energy stored in a spring is equal to half the spring constant multiplied by the square of the extension
• Moments are turning forces, calculated as force × distance to the pivot, with the unit being newton meters, and balanced moments prevent an object from turning
• Pressure is force divided by area, measured in N/m² or pascals (Pa), and can be calculated using the equation p = hρg for liquid pressure
• Gas pressure is due to gas particles colliding with surfaces, increased by adding more gas, reducing volume, or raising temperature to make particles move faster
• Acceleration is the rate of change of speed, measured in m/s², with negative values indicating deceleration or downward motion, and gravitational acceleration is 9.8 m/s²
• Velocity-time graphs can show distance traveled, with the area under the graph representing displacement, and Newton's equations of motion predict an object's behavior when accelerating
• Newton's first law states that with no resultant force, an object's motion is constant, inertia describes the tendency for motion to stay constant unless acted on by a force
• Newton's second law involves unbalanced forces, F = ma, proving it can be done practically using a trolley on a track with varying masses to measure acceleration
• Newton's third law states that for every action force, there is an equal and opposite reaction force, explaining interactions between objects like skaters or the Earth and a ball
• Stopping distance for a car is the sum of thinking distance and braking distance, with doubling speed quadrupling braking distance due to kinetic energy calculations
• Doubling your speed quadruples your braking distance because your car needs to lose all of its kinetic energy, which is equal to half MV squared
• If you double the velocity, the kinetic energy increases by a factor of 4; if you triple the speed, kinetic energy goes up by a factor of 9, increasing both braking distance and momentum
• Factors affecting thinking distance: distractions, alcohol, drugs; braking distance can be influenced by the condition of brakes, tires, road, and weather
• Momentum is equal to mass times velocity; it's a vector, meaning negative momentum occurs if velocity is negative
• In collisions, kinetic energy isn't always conserved, but total momentum always is; calculations may involve careful handling of pluses and minuses
• Total momentum before an event equals total momentum after; for two objects moving, it's M1U1 + M2U2 or M*V if they couple together
• Newton's second law states F=ma; force can also be expressed as change in momentum over time, showing the relationship between force and momentum change
• Seat belts, airbags, and crumple zones in cars increase the time taken for momentum change, reducing the force felt in accidents
• Waves transfer energy without transferring matter; longitudinal waves have oscillations parallel to energy transfer, like sound waves, while transverse waves have perpendicular oscillations, like light
• Sound waves cause the eardrum to vibrate, converting into signals for the brain; the human ear can hear frequencies between 20 Hz and 20 kHz
• EM waves can travel through a vacuum; the EM spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays
• Light waves change speed and direction when moving between mediums, known as refraction; specular reflection occurs off smooth surfaces, while diffuse reflection happens off rough surfaces
• Lenses use refraction to converge, diverge, or spread out light rays; convex lenses can make rays converge to a focal point
• When objects are very close to a lens, the image formed can be magnified and virtual; concave lenses always produce virtual images that are diminished and upright
• Color perception results from different wavelengths of light being absorbed and reflected by objects, affecting the colors we see
• A black body is an object that perfectly absorbs and emits all wavelengths of radiation, a concept applied to objects like stars or planets
• If a body absorbs radiation at a greater rate than it emits, its temperature will increase, leading to increased radiation emission
• A permanent magnet is a metal with molecules permanently aligned to produce a magnetic field, exerting a force on particles and electrons
• The two ends of a magnet are named North and South Pole, aligning with the Earth's magnetic field; magnetic field lines are complete loops from North to South Pole
• Current flowing through a wire produces a magnetic field, with field lines as concentric circles around it; the motor effect causes a wire in a magnetic field to experience a force
• The force on a wire due to the motor effect is calculated using the equation F = BIL, where F is force, I is current, L is length of the wire, and B is magnetic flux density