Physics P2
- Created by: felixshears
- Created on: 17-01-17 13:52
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
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
Velocity Time Graphs
Gradient = acceleration
Flat = steady speed
Steeper = greater acceleration
Uphill = accelerating
Downhill = decelerating
Curve = changing acceleration
Acceleration = vertical change/horizontal change
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
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
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
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
Circuit Symbols
Circuits
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
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
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
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
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
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
Alpha, Beta and Gamma
Less penetrative = more ionising
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
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
Life Cycle of Stars
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