Physics P2


Resultant Forces

Reultant force is overall force on an object

Stationary object - resultant force of 0 Newtons

No resultant force means no change in velocity

Resultant force - acceleration

Along straight line just add and subtract

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Distance Time Graphs

Gradient = speed

Flat = stopped

Straight up/down = steady speed

Steeper = faster

Downhill = back to starting point

Upward curve = acceleration

Downward curve = deceleration

Speed = vertical/horizontal

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Velocity Time Graphs

Gradient = acceleration

Flat = steady speed

Steeper = greater acceleration

Uphill = accelerating

Downhill = decelerating

Curve = changing acceleration

Acceleration = vertical change/horizontal change

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Forces and Breaking

When a vehicle travels at a steady speed the resistive forces balance the driving force

Stopping distance = distance covered in tme between driver spotting hazard and coming to stop

Reaction time could be affected by alcohol

Work done = energy transfered

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Forces and Terminal Velocity and Elasticity

Friction - slows everything down

Air resistance increases as speed increases

Terminal velocity - when resultant force is zero as frictional force = accelerating force

Streamlined = less drag

Force applied to elastic object results in stretching and elastic potential energy

Extension of elastic object is proportionate to the force applied until point of proportionality is reached and material permanently stretched 

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Momentum and Car Design

Momentum - a property of moving objects

Greater mass + greater velocity = greater momentum

When a force acts on an object it cause change in momentum

Momentum before an event = momentum after an event

Cars are designed to convert kinetic energy safely in a crash 

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Static Electricity

Build-up of static is caused by friction

Occurs when negative charges rub with positive charges and the charged objects attract small objects nearby

Opposites attract

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Circuit Symbols


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Current - flow of eleectrical charge in circuit

Potential difference = voltage - pushes current round

Resistance - something in circuit that slows the flow down and increases with temperature

Ammeter - Current                                                                                                                             Series                                                                                                          

Voltmeter - Voltage                                                                                                                              Parallel around component being measured

Series circuit - Circuit broken if anything removed                                                                                        Voltage shared                                                                                                                  Current same everywhere                                                                                                    Resistance adds up                      

Parallel circuits - Voltage same across components                                                                                       Current shared

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Circuits (2)

Diode  - used to regulate voltage in circuits and lets current flow freely in one direction

Light-Emitting Diodes (LEDs) - diode that emmits light when a current flows through it

Light-Dependant Resistor (LDR) - resistor that depends on intensity of light (works best in darkness)

Thermistor - heat dependent resistor (resistance highest in cool conditions)

Energy is transferred in circuits

More efficient = wastes less energy

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Household Electricity

AC - Alternating current that constantly changes direction

DC - from cells and batteries and one direction

Oscilliscope - time for one cycle = one peak to another

Blue cable - neutral 

Brown cable - live wire

Green and yellow earthwire - prevents fire by carrying electricity to the earth

Plug - metal parts made of copper and brass to conduct electricity and case + cable insulators made of rubber and plastic as good insulators

Wiring plug - right coloured wire connected to each pin and screwed in and cable pin fastened

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Fuses and Earthing

If the live wire touches the metal case the current flows through the case and down out the earth wire

If a current in a fuse wire exceeds the fuse rating it will melt and break the circuit

Same occurs with circuit breakers but instead a switch is flicked so easily reset

Double insulation - no earth wire

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Atomic Structure

Nucleus - tiny but has large mass, contains protons + neutrons and positively charged

Electrons whizz around rest of atom

Proton: Mass = 1  Charge = +1

Neutron: Mass = 1  Charge = 0

Electron: Mass = 0  Charge = -1

Number of protons = number of electrons

If atom is charged it's an ion

Isotopes - atoms with same number of protons but different number of neutrons

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Atoms and Radiation

Radioactive atoms give out radiation from the nuclei of their atoms

Radioactive decay is random

Background radiation is from - unstable isotopes/space/nuclear accidents

Half life - the average time it takes for the number of nuclei in a radioactive isotope to half

Can be used in: smoke detectors (alpha), tracers (beta) and radiotherapy (gamma)

Radiation kills cells

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Alpha, Beta and Gamma

( penetrative = more ionising

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Nuclear Fission

The splitting of an atomic nucleus

Occurs with Uranium -235 or Plutonium -239

Chain reaction

1) Nucleus absorbs a neutron

2) Makes nucleus unstable and makes it split

3) From this more neutrons are given off by nucleus 

4) These neutros are absorbed by other nucleus and chain reaction ocurs

Produces lots of energy but is dangerous

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Nuclear Fusion

When two light nuclei join together to create a larger nucleus

Produces lots of energy

No waste or nuclear danger

Requires extremely high temperatures so no reactor in the world is producing electricity yet

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Life Cycle of Stars


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absolutely brilliant. thanks very much.

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