FORCES AND MOTION

EQUATIONS $v = d/t$

$w = mg$

$a = Δv/t$

$M = mv$

$v^2 = u^2 + 2as$

Hookes law:

• for a spring: F = kx

• F is the force being applied

• k is the spring constant

• x is the extension

FORCES

• forces can be either contact or non contact

a force acts on an object.

• for an example, me using normal contact force to push a glass of water.

Forces are vectors

MMOVEMENT AND SPEED

• speed is measured in m/s or km/h

• movement can be easily graphed using a distance time graph or velocity time graph

STOPPIGN DISTANCE

$b.d = t.d + s.d$

braking distance = thinking distance + stopping distance

FACTORS THAT AFFECT THIS

ELECTRICITY

THINGS TO KNOW Current = I = measured in Amperes(A)

Voltage = V = measured in V, sometimes called P.d

Resistance = R = measured in ohms (Ω)

Power = P = measured in Watts (W)

Charge = Q = measured in couloumbs

conductivity = sigma

USEFUL FORMULAE:

• $V = IR$

• $P = IV$

• $E = IVt$

• $Q=It$

• $E = Qv$

CURRENT:

1. current is the rate of flow of charge, and can be thought of as how fast a train is going.

2. current is given by I = Qt,

3. Q is given in couloums and t is measured in seconds.

4. in metals, current is due to the flow of electrons, whereas in solutions , this can be the flow of ions.

5. current is measured with an ammeter connected in series with the component

VOLTAGE

1. voltage can be thought of as how many people each carriage is carrying in a train

2. Voltage is measured as the work done per unit of charge in moving between tow points in a circuit,

3. $V = EQ$

4. it is measured with a voltmeter placed in parallel across the component

1. the higher the voltage, the greater the current.

RESISTANCE

1. the resistance of a component is measured in ohms (omega) and can be found with

2. $V = IR$

3. the greater the resistance, the harder it is for current to flow through the component, and more heat is released leading to energy waster.

4. In an ohmic conductor (resistor), the current is directly proportional to the voltage.

5. A thermistor is a resistor whose resistance decreases as the temperature increases

6. a LDR ( light depended resistor is a resistor whose resistance decreases as light intensity increases.)

Electric circuits

CHARGE & STATIC ELECTRICITY

• measured in coulombs (C)

• there are positive and negative charges.

• opposite charges attract and negative charges repel

• Charge is how much total current passes over a period of time

Metals, as conductors, allow electron flow, while plastics, as insulators, restrict it. Friction from rubbing two insulators transfers electrons, charging them. The material losing electrons becomes positively charged, with charge magnitude equal on both due to identical electron loss/gain.

DANGERS OF ELECTROSTATIC CHARGES:

1. Static charges pose a risk of electric shock; if a person touches an object with a large amount of static charge, electrons will flow through the person’s body to the earth.

2. when fuelling aircraft and tankers, if enough charge builds up on the vehicle or pump, it can create a spark and ignite the fuel.

SAFTEY MEASURES WHEN USING ELECTROSTATIC CHARGES:

1. Earthing involves offering electrons an alternative pathway to the earth:

2. This prevents too much electrostatic charge from building up on the surface of an insulator, reducing electric shock and its harm.

USES OF ELECTROSTATIC CHARGES INCLUDE

INKJET PRINTER:

• drops of ink are charged and pass between two charged metal plates. the droplets are attracted to the plate with the opposite charge and repelled the the other one, effectively deflecting it towards a specific index on the page

PHOTOCOPIER

• the image of a document is projected onto a positively charge plate; where light falls onto the plate, the charge leaks away. Negatively charged toner particles are attracted to the remaining positive areas.

WAVES

GENERAL WAVES KNOWLEDGE

• $v = x$

• $v = fλ$

• $w = 1/t$

Waves are split into two different types:

here we can see the different aspects of a transverse wave, including the wavelength, amplitude, crests and peaks.

here we can see the different aspects of a longitudinal wave, incliuding compressions and rarefactions.

ELwctromagnetic spectrum

• radio waves, microwaves, infrared radiation, visible light, UV light, X rays, Gamma rays

• the electromagnetic waves in each of these bands have different characteristics such as

• - how they are produces

• - how they interact with matter

• -their practical applications.

WAVE BEHAVIOUR

When a wave meets a boundary between two materials, 3 things can happen:

1. Absorption

2. Transmission

3. Reflection

TRANSMISSION:

1. Waves travel at different speeds in materials with different densities

2. If the wave hits a boundary it changes speeds

3. If the wave hits a wave at a boundary at an angle, the change in speed causes a change in direction → this is called rare-fraction

4. The greater the change in speed the more the wavelength

5. The frequency of a wave stays the same when crossing a boundary, because of $v = fλ$, this means a change in speed is caused by a change in wavelength

REFLECTION:

We can use ray diagrams to visualise this:

SOUND

Sound travels as a wave

• sound waves are caused by oscillating objects

• The vibrations are passed through the surrounding medium as a collection of compressions and rare-fractions → sound is a type of longitudonal wave

• Sound cant travel in space because its mostly a vacuum

HEARING SOUND Sound waves that reach your eardrums cause it to vibrate

These vibrations are passed onto tiny bones in your ear called

• Ossicles

• semicircular canals

• Cochlea

MAGNETISM

RADIOACTIVITY

Atomic Structure:

• Nucleus made of neutrons and protons surrounded by shells of electrons

• Protons and neutrons have roughly the same mass, while electrons are much lighter

• Protons are positively charged, electrons are negatively charged, and neutrons have no charge

• The number of protons in an atom's nucleus determines the atomic number and identifies the element

ALPHA PARTiCTLES

• an alpha particle consists of 2 protons and 2 neutrons
  • They do not pentrate very far
  • They are strongly ionising

A: 4 2

BETA PARTICLES:

• Beta minus particles are fast moving electrons released by the nucleus

• Beta plus particles are fast moving positrons

• They are moderately ionising

B; 0 -1

GAMMA PARTIACLES

• Penetrate far into materials without being stopped and will travel a long distance through air

• This means they are weakly ionising

• They can be absorbed by thick sheets of lead or metres of concrete

Types of background radiation:

• Medical use

• Cosmic rays

• Buildings

• Radon Gas

• Rocks

• Short half life means → activity falls quickly

• Long half life means → activity falls slowly