Physics definitions

Base Quantities and SI Units

Length: meters (m)
Time: seconds (s)
Mass: kilograms (kg)
Temperature: Kelvin (K)
Electric Current: Ampere (A)

Common Prefixes

mega (M): *10^6

kilo (k): *10^3
centi (c): *10^-2
milli (m): *10^-3
micro (μ): *10^-6

Time

Measured using stopwatches, clocks, and digital timers. 1hr = 60 mins, 1 min = 60 secs

Measuring Length

Use a meter rule for up to 1 m, measuring tape for >1 m, and a micrometer for small lengths like wire thickness.

Measuring Volume

For liquids, use a measuring cylinder. For regular solids, use volume = lengthwidth height, area of base*height. For irregular solids, use the displacement method: measure initial water volume V1, submerge the object, measure new volume V2, and calculate V2 - V1

Measuring thickness of paper

Measure thickness of 100 sheets of people, divide the reading by number of sheet to get the thickness of 1 sheet, repeat and take average

Measuring oscillation period of pendulum

Reset your stopwatch to zero before making measurements. Measure time of 20 oscillations/cycles in one go, divide the reading by number of oscillations, repeat and take average

Mass

A measure of the quantity of matter in an object at rest relative to the observer; it is measured using a balance. To find the mass of a liquid measure the mass of the empty container first (m1). Then measure the mass of the container and liquid together (m2). Finally calculate the difference to get the mass of the liquid alone (m2-m 1).

Weight

The gravitational force on an object that has mass. W=mg where g= 9.8 N/kg and is equal to the acceleration of freefall

Gravitational field strength (g)

force per unit mass (N/kg)

Density

Mass per unit volume of a substance. row = mass/volume. (kg/m^3 or g/cm^3) Objects made of the same material have the same density, even if these objects are of different sizes and masses. Temperature can affect the density of a substance. Increasing the temperature decreases the density. Decreasing the temperature increases the density.

Measuring the density of a regular solid

1. Measure the mass of the object using a balance. 2. Measure the length, width and height and calculate the volume of the object. 3. Calculate density using mass/volume

Measuring the density of a liquid

1. Measure the mass of an empty measuring cylinder. 2. Pour the liquid into the cylinder and measure the new mass. 3. The difference is the mass of the liquid. 4. Record the volume of the liquid from the measuring cylinder scale. 5. Calculate density using mass/volume

Measuring the density of an irregular solid

1. Measure the mass of the object using a balance. 2. Pour some water into a measuring cylinder and measure the initial volume. 3. Gently put the object into the measuring cylinder and record the new volume. 4. Calculate the difference to find the volume of the object. 5. Calculate density using mass/volume

Floating and Sinking

Objects or liquids that are less dense than water will float on top of water. Objects or liquids that are more dense than water will sink in the water.

Scalars

Quantities with only magnitude (size). distance, speed, time, mass, energy, temperature

Vectors

Quantities with magnitude and direction. force, weight, velocity, acceleration, momentum, electric field strength, gravitational field strength

Speed

Speed is distance per unit time s=d/t or v=d/t (m/s or km/h)

Average speed

total distance travelled/total time taken

Velocity

speed in a given direction

Acceleration

Change in velocity per unit time. a = delta v/t or v-u/t (m/s^2) Deceleration is when velocity decreases aka Negative acceleration

Distance-Time Graph

The slope/gradient represents speed. If its an upwards line, its at constant speed, if its horizontal then its at rest. Steeper the line, higher the speed. If the slope is curved, its acceleration because speed is changing.

Speed-Time Graph

The slope represents acceleration, and the area under the graph represents distance travelled. If its an upwards line, its acceleration, downwards line then deceleration. If its horizontal then its constant speed. If the slope is curved, its increasing or decreasing acceleration.

Hooke’s Law

The extension of a spring is directly proportional to load on it, as long as limit of proportionality is not exceeded F=kx (N/cm). LOP curves towards extension

Spring constant

force per unit extension

Resultant of Forces in a Straight Line

If forces are in the same direction, they are added. If forces are in opposite directions, they are subtracted

Solid friction

the force between two surfaces that may impede motion and produce heating (kinetic to heat).

Drag

acts on an object moving through a liquid or a gas. Drag increases if: 1. Speed of the object increases and 2. Area of the object increases.

Newton's First Law of Motion

An object either remains at rest or continues in a straight line at constant speed unless acted on by a resultant force. A resultant force may change the velocity of an object by changing its direction of motion or its speed.

Newton's Second Law

Resultant Force = mass x acceleration F= ma (N). Force and acceleration are in the same direction.

Circular Motion

Motion in a circular path is due to a force perpendicular to the motion. The resultant force is always towards the center of the circle. The acceleration is towards the center of the circle. With mass and radius constant, if force↑, speed ↑. With mass and speed constant if force↑, radius decreases. An increased mass requires an increased force to keep speed and radius constant

Objects falling in a vacuum (no air resistance)

Falls at constant acceleration of 9.8 m/s^2, called the acceleration of freefall, due to the weight of the object.

Objects falling in air (with air resistance)

1. Only weight acts downwards, so object falls at constant acceleration of 9.8 m/s^2

2. As speed increases, upward air resistance increases, so downward resultant force decreases, which decreases the acceleration.

3. Upward air resistance becomes equal to downward weight, resultant force and acceleration are zero, so object falls at a constant maximum speed (called terminal velocity)

Momentum

Product of mass and velocity. p=mv (kg m/s or Ns)

Impulse

Force * change in time. = Ft = mv-mu (impulse = change in momentum)

Resultant force

change in momentum per unit time. F = mv-mu/delta t. (N)

Law of Conservation of Momentum

total momentum of a closed system is always conserved (constant) sum of momentum before = sum of momentum after

Moments

force * perpendicular distance from the pivot (Ncm or Nm). Clockwise and anticlockwise. At pivot there is no moment.

Equilibrium

No resultant force, There is no resultant moment.

Principle of moments

Total clockwise moments = Total anticlockwise moments

Centre of Gravity (CoG): A point in an object where weight is considered to act. Regular shapes: The CoG is at the geometrical center. Irregular shapes: The CoG is typically located nearer to the heavier portion of the object.

Finding CoG of a Plane Lamina

Hang the card using a pin, stand and clamp from one end. When the card balances, the center of mass is somewhere below the pin.
Attach a plumb line on the pin and draw a vertical line along the thread.
Repeat steps 1 & 2 from another point on the card. The point of intersection of the lines is the center of mass.

Stability

To Increase Stability: Lower the center of mass and widen the base of the object. To Decrease Stability: Raise the center of mass and narrow the base.

Kinetic

Increases as speed of object increases. 1/2mv^2 (Joules J)

Gravitational Potential

Increases as height of object from ground increases. mgdeltah (J)

Chemical

Food, fuel, batteries, wood, humans, plants, animals.

Elastic (Strain)

Increases when an object is stretched, compressed or bent (springs, bows, etc.)*
Nuclear

Internal (thermal)

Total kinetic energy of the molecules of a substance, increases when temperature of an object increases.

Electrostatic and Magnetic

Energy stored in an electric field and magnetic field respectively.

Methods of energy transfers

1. Force → mechanical work

2. Electric current → electrical work

3. Heating

4. Waves (light or sound)

Law of Conservation of Energy

energy cannot be created nor destroyed but can only be changed from one form to another

Work Done: the transfer of energy. mechanical work: W = delta E = Fd (J). Force and distance in same direction

Power

work done per unit time or energy transferred per unit time. P = W/t = delta E/t = fd/t (Watt W)

Efficiency (%)

useful energy output/total energy output * 100 or useful power output/total power input *100

Pressure

force per unit area. P = F/A (Pascal Pa). Pressure↑ as force ↑ or SA decreases. Pressure decreases as Force decreases or SA increases. Total pressure = sum of liquid amd atmospheric pressure

Pressure in Liquids

delta P liquid = rowgdeltah. Pressure beneath liquid ↑ if depth and density of liquid. Pressure decreases if depth and density of liquid decreases

Sun

Radiation from the Sun is the main source of energy for all our energy resources except geothermal, nuclear and tidal. The energy in the Sun is produced by nuclear fusion.

Geothermal resources

thermal -> kinetic -> electrical. Renewable, reliable, no pollution but difficult to find a location where rocks are hot enough

Nuclear fuel

nuclear -> heat -> kinetic -> electrical. Reliable, high-energy output but nuclear waste, ionizing radiation, non-renewable

Energy in tides

gravitational -> kinetic -> electrical. Renewable, no pollution but unreliable, low energy output, difficult to find a location to build

Fossil fuels

Fossil fuels were originally living creatures which were previously alive because of the Sun

Chemical energy in fossil fuels, biofuels

chemical -> heat -> kinetic -> electrical. Reliable, high-energy output but air pollution, greenhouse gases, non-renewable

Hydroelectric

The Sun evaporates the ocean's water, creating clouds that rain down to form lakes and rivers.

Energy in hydroelectric

gravitational -> kinetic -> electrical. Renewable, no pollution but unreliable as it relies on rain and rivers, difficult to find a proper location to build

Wind

temperature differences between different regions of the earth due to the Sun cause the air to flow

Heat from sun warms atmosphere to produce wind

kinetic -> electrical. Renewable, no pollution but unreliable as it relies on wind speed that can changr, low energy output, needs a lot of space with high-speed wind

Energy in waves

kinetic -> electrical. Renewable, no pollution but unreliable as it relies on waves coming and going, low energy output.

Solar

light and heat (infrared) energy from the sun

Light from sun, solar cells

light -> electrical. Renewable, no pollution but unreliable as it does not generate electricity at night, needs a lot of space with good sunlight

Unit 2:
Kinetic Particle Model of Matter
Solid - Separation: Fixed shape and a fixed volume, particles are tightly packed no separation
Arrangement: regular, organised pattern
Motion: particles vibrate about their position in the structure. Very strong bonds between molecules

Liquid - Separation: Fixed volume but not a fixed shape, particles are close together and some separation, most are touching,
Arrangement: Irregular. particles are randomly arranged.
Motion: particles slide over each another and move with random motion throughout the container. Strong bonds between molecules

Gases - Separation: No fixed shape nor volume, particles are widely spaced
Arrangement: particles are randomly arranged
Motion: particles move rapidly in all directions, colliding with each other and the sides of the container. Very weak bonds between molecules

Temperature

Average Kinetic Energy of the molecules in a substance (C degrees celcius). If the temperature of an object increases, the molecules move faster. If temperature decreases, the molecules move slower.

Absolute Zero

The lowest possible temperature at which particles have the least kinetic energy (-273 degrees Celcius)

Celsius to Kelvin

C degrees + 273

Melting and freezing

happen at the same temp called melting point. MP of ice is 0 degrees C

Melting and Boiling

Molecules gain heat energy to weaken or break bonds and move farther apart. They do NOT gain kinetic energy, so the temperature remains constant.

Boiling and condensing

happen at the same temp called boiling point. BP of water is 100 degrees C

Condensation and Freezing

Molecules lose heat energy to strengthen bonds and move closer together. They do NOT lose kinetic energy, so the temperature remains constant.

Evaporation: The most energetic molecules on the surface of the liquid break their bonds and escape. Cooling Effect: Less energetic molecules remain, so the temperature of the remaining liquid decreases. If this liquid is on an object or body , it will absord heat from the object, cooling it.

Increasing Rate of Evaporation

Increase temperature; molecules have more energy. Increase surface area; more molecules are on the surface that can escape. Increase air movement above the surface; wind or air currents push molecules away from the liquid surface

Boiling vs Evaporation

Thermal Expansion

Increase in volume of a substance when its temperature increases. Molecules move faster and farther apart (spacing increases). Contraction: Decrease in volume of a substance when its temperature decreases

Properties that affect the amount of thermal expansion

1. State, gases expand more than liquids, liquids expand more than solids, because gases have weaker bonds than liquids, and liquids weaker than solids.

2. Temperature, the higher the temperature the more a substance expands.

3. Initial volume, the higher the initial volume the more a substance expands.

Applications of Thermal Expansion

1. Thermometers use liquid expansion to show temperature
2. Bimetallic strips are made of two different solid strips stuck together. When heat one expands more than the other so the strip bends. Used in thermostats and old fire alarms.
3. Fitting rings over rods (rings over wheels), heating iron rings make them expand so they can fit on wheels

Consequences of Thermal Expansion

1. Railway tracks can can deform (buckle) at very high temperatures. Solved by leaving small gaps between sections of a railway track.
2. Bridges and roads can deform and fracture at very high temperatures. Solved by leaving small gaps between sections of bridges.
3. Hanging electric cables can expand if it gets too hot and touch cars on the road. They can also contract during cold seasons and tear if they contract too much.

Brownian Motion

The random and irregular motion of microscopic particles (like smoke or pollen) in a suspension caused by random collisions with air or water molecules from all directions.

How gas particles apply pressure

Gas particles move freely, collide with the walls of the container, experience a change in momentum over time, which applies force over the area of the walls.

Effect of Temperature on Gas Pressure (constant volume)

Describe: Temperature and pressure of a gas, in a closed container, are directly proportional.
Explain, in terms of molecules: When temp increases pressure increases, particles have larger velocity, higher rate of collision frequency, and collide with larger force

Effect of Volume on Gas Pressure (constant temperature)

Describe: Volume and pressure of a gas, at a constant temperature, are inversely proportional.
Explain, in terms of molecules: When volume decreases pressure increases, spacing between gas molecules decreases, so higher rate of collision frequency

Boyles Law

when temp is constant. P1V1 = P2V2

Internal Energy: Total kinetic energy of the molecules in a substance

Specific Heat Capacity c

Energy needed to raise the temperature of a unit mass (1kg) by a unit temperature (1 degree C). c = delta E/m delta t (J/kg degree C) or just deltaE = mcdeltaT (J)

Experiment to measure c of a solid object or liquid

Conduction

Non-metals: When heated, the atoms (molecular lattice) vibrate and transfer heat to nearby atoms (lattices.) Metals: When heated, the atoms (molecular lattice) vibrate and transfer heat to nearby atoms (lattices) AND free electrons move to transfer heat to distant atoms (lattices.)

Good conductors of heat

copper, iron, steel, aluminium

Poor conductors of heat

plastic, rubber, wood, glass, cloth, wool. Liquids and gases are poor conductors of thermal energy because their molecules are farther apart.

Experiment to demonstrate good and poor conductors of heat

1. Stick balls to both rods using wax
2. Heat the rods from one at the same rate
3. The better conductor will melt the wax faster so more balls will fall.
4. The worse conductor will melt the wax slower so less balls will fall.

Convection

Hot liquids or gases rise and cold liquids or gases sink because hot fluids/gases are less dense. when liquids/gases are heated their volume increases, without a change in mass, so their density decreases.

Radiation

Thermal energy transferred using infrared (electromagnetic) waves. Can travel through vacuum, in straight lines, and in all directions

Factors affecting rate of radation emission

1.Surface area, as area increases the rate of emission of infrared waves increases

2. Surface temperature, as the temperature increases the rate of emission of infrared waves increases