Year 9 Physics End of Term 3 Assessment Revision

Standard Unit System and Conversions

• Length Conversions:     * $1\,\text{cm} = 10\,\text{mm}$     * $1\,\text{m} = 100\,\text{cm}$     * $1\,\text{km} = 1000\,\text{m}$

• Time Conversions:     * $1\,\text{hour} = 60\,\text{minutes}$     * $1\,\text{minute} = 60\,\text{seconds}$     * $1\,\text{hour} = 60 \times 60 = 3600\,\text{seconds}$     * To convert from hours to seconds: $\text{Hours} \times 3600 = \text{Seconds}$     * To convert from seconds to hours: $\text{Seconds} \div 3600 = \text{Hours}$

Movement and Position

• Key Definitions and Principles:     * Speed: Defined as the distance travelled per unit time.     * Velocity: Defined as the speed in a given direction.     * Acceleration: The change in velocity per unit time. If speed is changing, the object is either accelerating or decelerating.     * Free Fall: The acceleration of free fall near to the Earth is constant.

• Units of Measurement:     * Distance: metres ($\text{m}$)     * Time: seconds ($\text{s}$)     * Speed and Velocity: metres per second ($\text{m/s}$)     * Acceleration: metres per second squared ($\text{m/s}^2$)

• Essential Formulas:     * Acceleration Calculation: $\text{acceleration} = \frac{\text{change in velocity}}{\text{time taken}}$     * Symbolic form: $a = \frac{v - u}{t}$     * Relationship between final speed, initial speed, acceleration, and distance: $\text{(final speed)}^2 = \text{(initial speed)}^2 + (2 \times \text{acceleration} \times \text{distance})$     * Symbolic form: $v^2 = u^2 + 2as$

• Distance-Time Graphs:     * Gradient: Represents the velocity.     * Horizontal Line: Indicates the object is stationary.     * Negative Gradient: Indicates the object is returning back to the starting point.     * Zero Displacement: If the distance/displacement is zero, the object is back at the starting point.

• Velocity-Time Graphs:     * Gradient: Represents the acceleration.     * Negative Gradient: Indicates deceleration (negative acceleration).     * Horizontal Line: Indicates constant speed.     * Speed is Zero: Indicates the object is at rest.     * Area Under the Line: Represents the total distance travelled.     * Curved Line: Indicates that the acceleration is changing.

Energy Stores and Transfers

• Energy Stores: Energy can be transferred between eight different stores as a result of a process or event:     * Chemical Store: Energy transferred into or away during chemical reactions.     * Kinetic Store: Energy held by moving objects.     * Gravitational Potential Store: Energy gained by objects lifted through a gravitational field.     * Elastic Potential Store: Energy held by objects that are stretched, squashed, or bent.     * Thermal Store: Energy held by all objects; the hotter the object, the more energy in this store.     * Magnetic Store: Energy held by magnetic materials interacting with each other.     * Electrostatic Store: Energy held by interacting charged objects (e.g., electrons and protons).     * Nuclear Store: Energy released from atomic nuclei during nuclear reactions.

• Energy Transfer Pathways:     * Mechanically: For example, when gravity accelerates an object and gives it kinetic energy.     * Electrically: For example, when a current passes through a lamp, emitting light and heat.     * By Heating: For example, using a fire to heat up an object.     * By Radiation: For example, vibrations causing sound waves through air, or an object emitting electromagnetic radiation.

• Law of Conservation of Energy: Energy is always conserved. The total energy before an event is equal to the total energy after.

• Efficiency:     * Efficiency is the ratio of useful energy output to total energy supplied.     * Formula: $\text{efficiency} = \frac{\text{useful energy output}}{\text{total energy input}} \times 100\%$

• Sankey Diagrams:     * Visual representations of energy transfers using splitting arrows.     * Left-hand side (flat end): Represents the energy transferred into the system.     * Straight arrow pointing right: Represents the useful energy output (desired store).     * Bending arrows (downward/away): Represent wasted energy.     * Example (Lamp): Total electrical energy ($100\,\text{J}$) splits into light energy ($10\,\text{J}$ useful) and heat energy ($90\,\text{J}$ wasted).

Thermal Energy Transfer

• Conduction:     * Primarily occurring in solids and liquids through particle vibration.     * Mechanism: Molecules are heated, vibrate more, and collide with adjacent molecules, transferring heat from hot to cool parts.     * Insulators (Non-metals): Poor conductors that transfer heat slowly; used to reduce unwanted energy transfer in homes.     * Metals: Good conductors. Free electrons move between positively charged ions. Both ions and electrons vibrate when heated; free electrons collide with ions throughout the metal to transfer heat rapidly.

• Convection:     * Occurs in fluids (liquids and gases) because molecules are not fixed.     * Mechanism: Heated fluid expands, particles move further apart, and the fluid becomes less dense. This less dense fluid rises. Colder, denser fluid falls to take its place.     * Reduction: Preventing fluid circulation reduces unwanted convection.     * Examples: Water boilers, hot air balloons.

• Radiation:     * Transfer of thermal energy via infrared radiation (part of the electromagnetic spectrum).     * Medium: Does not require a medium to travel.     * Emission and Absorption Factors:         * Black bodies with dull textures: Best absorbers and emitters.         * White bodies with shiny textures: Best reflectors; poor absorbers and emitters.         * Shiny surfaces: Used on vacuum flasks to reduce energy transfer.         * Temperature and Area: Higher temperatures and larger surface areas increase the amount of infrared radiation emitted.

• Summary Table of Surface Properties:

Solids, Liquids, and Gases

• Density and Pressure:     * Density ($\rho$): Mass per unit volume, measured in kilograms per metre cubed ($\text{kg/m}^3$).     * Formula: $\rho = \frac{m}{V}$     * Pressure ($P$): Force per unit area, measured in Pascals ($\text{Pa}$).     * Formula: $P = \frac{F}{A}$

• Measuring Density Experimental Procedures:     * Liquids:         1. Find the mass of an empty measuring cylinder using a balance.         2. Fill with liquid and measure the new mass.         3. Mass of liquid = (Total mass) - (Cylinder mass). Alternatively, use the 'tare' button to zero the balance.         4. Read volume from the cylinder straight-on to avoid parallax error.         5. Calculate $\rho = m/V$.     * Regular Solids:         1. Measure mass on a balance.         2. Measure dimensions with a ruler and use a mathematical formula for volume.         3. Calculate $\rho = m/V$.     * Irregular Solids:         1. Measure mass on a balance.         2. Submerge in water and measure the volume of water displaced. The displacement equals the solid's volume.         3. Calculate $\rho = m/V$.

• Pressure in Fluids:     * Pressure in a gas or liquid at rest acts equally in all directions and causes force at right angles to surfaces.     * Pressure Difference Formula: $\text{pressure difference} = \text{height} \times \text{density} \times \text{gravitational field strength}$     * Symbolic form: $p = h \times \rho \times g$     * Depth: Pressure increases with depth because there are more particles (greater weight) above the point.     * Density: Higher density fluids have more particles per unit volume, increasing weight and pressure.

• Changes of State:     * Heating increases internal energy, leading to either temperature rise or change of state.     * Temperature Rise: Energy increases molecular kinetic energy (molecules vibrate/move more).     * State Change: Temperature stays constant. Energy is used to break bonds/forces between molecules to make them freer.         * Melting: Solid to liquid; molecules move from fixed positions.         * Boiling: Liquid to gas; molecules break bonds to become separate. Occurs throughout the liquid strictly at the boiling point.         * Evaporation: Escape of high-energy molecules from a liquid surface. Remaining molecules have lower average kinetic energy, cooling the liquid (e.g., sweating). Can happen at any temperature.         * To increase evaporation: Increase temperature, surface area, or provide a draught.

• States of Matter Characteristics:     * Solids: Molecules close together in a regular pattern; strong intermolecular forces; vibrations only.     * Liquids: Molecules close together in a random arrangement; weaker forces than solids; molecules move around each other.     * Gases: Molecules far apart in a random arrangement; negligible forces; rapid movement in all directions.

• Specific Heat Capacity:     * The amount of energy required to raise the temperature of $1\,\text{kg}$ of a substance by $1\,^{\circ}\text{C}$.     * Unit: Joules per kilogram degree Celsius ($\text{J/kg}^{\circ}\text{C}$).     * Formula: $\Delta Q = m \times c \times \Delta T$

• Ideal Gas Behavior:     * Gas molecules move rapidly and randomly; pressure is created by collisions with container walls.     * Force is exerted on walls because molecules change direction/velocity/momentum upon rebounding ($\text{Force} = \frac{\text{change in momentum}}{\text{time}}$).     * Absolute Zero: The temperature at which gas pressure is zero. This occurs at $-273\,^{\circ}\text{C}$.     * Kelvin Scale: Absolute zero is $0\,\text{K}$. Increment size is the same as Celsius ($1\,^{\circ}\text{C} = 1\,\text{K}$).     * Conversion: $\text{Temperature in Kelvin} = \text{Temperature in degrees Celsius} + 273$     * Temperature and Kinetic Energy: The Kelvin temperature of a gas is proportional to the average kinetic energy of its molecules.

• Gas Laws:     * At Constant Volume (Pressure Law): If temperature increases, pressure increases because molecules move faster and collide harder/more frequently.     * Formula: $\frac{P_1}{T_1} = \frac{P_2}{T_2}$ or $\frac{P}{T} = \text{constant}$     * At Constant Temperature (Boyle's Law): If volume increases, pressure decreases because molecules collide less frequently over a larger area.     * Formula: $P_1 \times V_1 = P_2 \times V_2$ or $P \times V = \text{constant}$

Summary of Essential Physics Formulas

• Density: $\rho = \frac{m}{V}$
• Pressure: $P = \frac{F}{A}$
• Fluid Pressure Difference: $p = h \times \rho \times g$
• Basic Acceleration: $a = \frac{v - u}{t}$
• Advanced Motion Equation: $v^2 = u^2 + 2as$
• Efficiency: $\text{efficiency} = \frac{\text{useful energy output}}{\text{total energy input}} \times 100\%$
• Change in Thermal Energy: $\Delta Q = m \times c \times \Delta T$
• Gas Pressure/Temperature Relationship: $\frac{P_1}{T_1} = \frac{P_2}{T_2}$
• Gas Pressure/Volume Relationship (Boyle's Law): $P_1 \times V_1 = P_2 \times V_2$
• Temperature Conversion: $T\,(\text{K}) = T\,(^{\circ}\text{C}) + 273$