Physics Notes Part 1

  Physics Important Notes

• The complete measurement is called a physical quantity.
• Numbers written using powers of ten are in scientific notation or standard form.
• Scientists use SI units (Le Systéme International d'Unités). SI unit of mass is the kilogram. SI unit of time is second.
• SI unit of length is metre. SI unit of volume is cubic metre. SI unit of work is joule. SI unit of frequency is hertz. SI unit of power is work. Force is measured in newtons. The time taken for one complete oscillation is a period.
• Quantities which have only magnitude are scalars. Quantities which have a direction, as well as a magnitude (size), are vectors.  Velocity is the speed of something and its direction of travel.
•  Reading shown when the result is known to be zero is zero error.
• Acceleration is a change in velocity per time. A negative acceleration is deceleration or retardation. Uniform acceleration means constant (steady) acceleration. Objects fall with the same downward acceleration 9.8 m/s² is the acceleration of freefall. If acceleration is not steady, it’s non-uniform.
•  On the graph, the line’s rise on the vertical scale divided by its rise on the horizontal scale is a gradient.
• Force is a push or a pull, exerted by one object on another. Types of force: upthrust, weight, tension, friction, air resistance, thrust. Upthrust, is an upward force from a liquid or gas that makes some things float. Weight is the gravitational force on an object. Tension, force in a stretched material. Thrust, is the forward force from an aircraft engine. Air resistance is a type of friction. Friction is, a force that opposes the motion of one material sliding past another. Two unbalanced forces are equivalent to a single force is the resultant force. The inward force needed to make an object move in a circle is centripetal force.
•  Newton’s first law of motion is if no external force acting on an object, it will remain stationary, if stationary. If no external force acting on an object, it will move at a steady speed in a straight line, if moving.
•  Newton’s second law of motion is force is equal to mass in acceleration.
• Newton’s third law of motion, if object A exerts force on object B, then object B will exert an equal but opposite force on object A. To every action, there is an equal but opposite reaction.
• When air resistance and weight are balanced, with no more speed is terminal velocity. The resistance to change in velocity is inertia.
• A downward pull from Earth is a gravitational force known as weight. A gravitational field is a region in which a mass experiences force due to gravitational attraction. Earth’s gravitational field strength is 10N/kg.
•  Momentum is mass into velocity. The resultant force is equal to the rate of change of momentum. Force into time is impulse.
•  Law of conservation of momentum, when two or more objects act on each other, their total momentum remains constant, provided no external forces are acting.
•  Law of conservation of energy is that energy can be stored or transferred, but it cannot be created or destroyed.
•  Laws of reflection: The angle of incidence is equal to the angle of reflection. The incident ray, reflected ray, and normal all lie in the same plane.
• The turning effect of a force is called a moment. The moment of a force (torque) about a point is force into a perpendicular distance from the point. If an object is in equilibrium, the sum of clockwise moments about any point is equal to the sum of anti-clockwise moments about that point.
• Although weight is distributed through an object, it acts as a single, downward force from a point called the centre of mass or centre of gravity.
• Object that is stretched and keeps a new shape is plastic. The force applied to the spring is load. Till a point, where the extension is proportional to load, is the limit of proportionality. A material obeys Hooke’s Law if, beneath its elastic limit, the extension is proportional to load. Dividing load by extension gives the same value as the spring constant.
• The lowest temperature is absolute zero. (-273 Degree Celsius) Kelvin scale is a thermodynamic scale.
• Instruments that measure atmospheric pressure are barometers. In weather forecasting, the millibar(mb) is used as a pressure unit. The manometer measures the pressure difference. The method of finding the density of a liquid is to use a small float called a hydrometer.
•  Boyle’s Law: For a fixed mass of gas at a constant temperature, the pressure is inversely proportional to the volume.
•  Work done is force into distance moved in the direction of force. The rate at which work is done is power.
• Kinetic energy is energy stored by an object because of its motion. Gravitational potential energy is energy stored by an object lifted upwards against the force of gravity. Elastic (strain) energy is a stretched rubberband that stores energy so does a compressed spring. Potential energy is when objects or particles store energy because of their position. Chemical energy is energy stored in chemical bonds. Electrostatic energy: Electric charges attract each other but are held apart, they store energy. In nuclear energy, when particles are rearranged or the nucleus splits, the stored energy is released. Thermal energy, when a hot object cools, its particle slows down, so the energy is lost. It is related to internal energy. Magnetic energy: Two magnets attract each other but are held apart, they store energy.
• Efficiency: An engine does useful work with some of the energy supplied to it, but the rest is wasted as thermal energy (heat).
• Energy released by the nuclear reaction which splits uranium atoms is nuclear fission. Coal, oil and natural gas are called fossil fuels. Shale gas is extracted from shale by the process of fracking. (hydraulic fracturing).
• Scientists have developed a model called kinetic theory to explain how solids, liquids and gases behave. Solid particles are held closely together by strong forces of attraction called bonds. Everything is made from about 100 simple substances called elements. An atom is the smallest possible amount of an element. Most materials are groups of atoms called molecules. As particles drift through the air, they wobble about in zigzag paths known as Brownian motion. The total kinetic and potential energies of all atoms or molecules in the material are internal energy. In atoms, tiny particles are electrons.
• Objects at the same temperature have the same average kinetic energy per particle. The higher the temperature, the greater the average kinetic energy per particle. If the bar is heated, its volume increases slightly, this effect is thermal expansion. Thermal energy transferred from the hot end to the cold end faster is conduction.
• Less dense water/air moves upwards and denser goes downwards, which is a convection current. Energy travels in electromagnetic waves. They heat things that absorb them, known as thermal radiation.
• When liquid below its boiling point changes into gas, is evaporation. Sweating and refrigerators use the cooling effect of evaporation. The energy needed to raise the temperature of 1 kg by 1 degree Celsius is the specific heat capacity.