Physics Flashcards
In a distance time graph how is : Speed represent Stationary/stopped represented How fast Going backwards Acceleration and deceleration Speeding up Slowing down
Speed - gradient Stationary - flat line How fast - steeper the graph Going back - downhill sections Acceleration/deceleration - curved lines Speeding up - steepening curve Slowing down - levelling off
What is the difference between speed and velocity
Speed is how fast you are going (e.g 30mph or 20m/s)
Velocity how fast you are going in a given direction (e.g 20m/s north)
How to calculate speed on distance time graphs
Speed = gradient = vertical/horizontal
E.g 500/30 = 16.7
What is acceleration
Acceleration is how quickly a velocity is changing
What is the acceleration formula
Acceleration = change in velocity / time
OR
Acceleration = (v-u)
-----
a x t
V= final velocity
U= initial velocityIn a velocity time graph how is Acceleration is represented Steady speed Acceleration/deceleration Distance travelled in a time interval Changing acceleration
Acceleration- gradient
Steady speed- flat sections
Acceleration- uphill sections
Deceleration- downhill sections
Distance travelled in a time interval - the area under any section of the graph
Changing acceleration- curve
How do you calculate acceleration from a velocity time graph
Acceleration=gradient= vertical change/horizontal change
How do you find out velocity from a velocity time graph
Simply found by reading the value of the velocity axis
How do you find the distance travelled on a velocity time graph.
It is equal to the area under the graph
What is gravitational force
It is the force of attraction between all masses
Gravity gives every thing a ……..
Weight
Gravity make all things accelerate towards the ground
What is the approximate acceleration ?
10m/s. ( on earth )
What is the difference between weight and mass ?
Mass - the amount of stuff in a object for any given object on any universe
Weight- is caused by the pull of gravitational force
The weight of an object is just the force pulling it towards the centre of the earth
What is the difference between weight on a different planet and mass on a different planet
Mass is the same any where on the universe
Weight is different depending on where it is
E.g 1kg mass will weigh less on the moon (1.6N) than it does on earth (10N) simply because the gravitational pull is less.
What is the unit for measuring gravity
And what is the equipment used for it
The unit for measuring gravity is: Newtons
It is measured using a Newton meter or a spring balance
What is the unit for mass
Kg (kilograms)
What is the formula for weight
Weight = mass x gravitational field strength
What is the units for weight
Newtons
What is earths gravitational field strength
g = 10N/kg
g - strength of gravity
What is the earths gravitational field strength
1.6 N
What is the resultant force
The overall force on a point or object
There are normally ……… Forces acting on a object
2 forces
The overall effect of these will decide its motion
E.g accelerate, decelerates or stays at a steady speed
If the forces are all acting along the same line
E.g parallel or opposite
how do you work out the overall force
Adding or subtracting them
E.g the resultant force on a stationary teapot with 10N pushing up and 10N pushing down
Then 10N - 10N = 0N
If something is stationary then all the forces are …..
Balanced
What does a resultant force mean ?
Not definition of what it is
It means a change in velocity
As if there is a resultant force acting on a object then it will change its state of rest or motion
If a car has a driving force of 1000N and a air resistance of 600N. Then what is the resultant force
400N
Because 1000N - 600N = 400N
If a resultant force on a stationary object is zero, the the object will …………. …………..
Remain stationary
If there is no resultant force there is no change in what ?
Velocity
If there is no resultant force on a MOVING object then …………..
The object will carry on moving at the same velocity
Formula for resultant force
F = ma. OR. A = f/m
F - resultant force in newtons
M - mass in kilograms
A - acceleration in meters per second square
What are reaction forces
When two objects interact the forces they exert on each other are equal and opposite
What is friction
Friction always slows things down
Friction always act in the opposite direction to movement
How to you get friction
Friction happens when there are two surfaces in contact
Or when a object passes through a fluid (drag)
How can you reduce drag
Keep the shape of the object streamlined
When does drag increase
When speed increases
How does terminal velocity work
- the object starts to fall
- The force of gravity is much more than the frictional force
- As the speed increases the friction builds up this gradually reduces acceleration
- Eventually the frictional force becomes equal to the accelerating force.
- This is when it reaches the maximum speed or terminal velocity
The terminal velocity of a object depends on it ………… And ……………
Shape and size
What is stopping distance
The total stopping time of a vehicle is the distance covered in the time between the driver first spotting a hazard and the vehicle coming to a complete stop.
What is thinking distance
The distance the vehicle travels during the drivers reaction time
Reaction time is the time between the driver spotting a hazard and taking action
What are the 2 factors that effect thinking distance
- How fast you are going
2. How dopey you are . E.g tiredness, drugs and drunk
What is braking distance
The distance the car travels under the breaking force.
What are the 4 main factors that effect braking distance
- How fast you are going
- How good your brakes are (minimum tread depth 1.6mm)
- How good the tyres are
- How good the grip is
What is meant by ‘ work done ‘
When a force moves an object through a distance ENERGY IS TRANSFERRED and WORK IS DONE
( basically when something moves something else is providing some sort of effort to move it )
What is the formula for work done
Work done = force x distance
What is gravitational potential energy
Is the energy that a object has by virtue of its vertical position in a gravitational field
(Work is done against the force of gravity because of the effort needed to lift a object. Which gains the object gravitational potential)
What is the formula for gravitational potential
Gpe = mass x g x height
Gpe = gravitational potential energy
What is kinetic energy
The energy of movement
What is the formula for kinetic energy
Kinetic energy = 1/2 x mass x speed
What does Ep stand for ?
It stands for gravitational potential energy
Ep and gpe are the same thing
What is the law on conservation of energy
Energy cannot be created or destroyed but only converted into different forms
Kinetic energy transferred is ……… ………..
Work done
(For example when a car is moving it has a lot of kinetic energy.to slow the car down the kinetic energy needs to be converted into other types of energy)
What is the formula for kinetic energy transferred
Kinetic energy transferred = work done by brakes
1/2mv² = F x D
M= mass of car passenger in kg V= speed of car m/s F= maximum braking force in Newtons D= braking distance in meters
What happens when something falls
It’s potential energy is converted into kinetic energy
so the further it falls the faster it goes
What is the formula for kinetic energy gained
Kinetic energy gained = potential energy lost
Some kinetic energy is converted into ………. And ……….
Heat and sound
What happens when work is done to an elastic object
It is stored as elastic potential energy
When you apply a force to a object you may cause it to ……….. And …………. …… ………
Stretch and change shape
What is an object called if it can go back to its original shape after the force has been removed
An elastic object
When work is done to an elastic object to change its shape what happens to the energy
It is NOT lost but is stored by the object as elastic potential energy which is then converted to kinetic energy when the force is removed and the object returns back to original shape
E.g a spring or elastic band bouncing back
Extension of a elastic object is directly proportional to …………..
Force
E.g the extension of a spring is directly proportional to the load of force applied
What is the formula for force
F= k x e
K= spring constant E= extension
What is the limit of proportionality for an elastic object
It is the maximum force a the elastic object can take and still expand proptionally
What is power
Power is the rate of doing work
I.e how much per second
It is not how strong something is
E.g a powerful machine is a machine that can transfer a lot of energy in a short space of time
What is the formula for power
Power = work done(energy transferred)/time taken
What is power measured in
Power is measured in watts in or j/s
What is one watt equal to
One watt = 1 joule of energy transfer per second
How do you calculate your power output
There are 2 ways
- Energy transferred is the potential energy gained (mgh)
Hence, power = mgh/time - Energy transferred is the kinetic energy you gain = 1/2mv²
Hence, power = 1/2mv² / time
What is momentum
Momentum is the property of a moving object
What is the formula for momentum
Momentum = mass x velocity
The greater the mass of a object and the greater it’s velocity the more …………. It has
Momentum
The total momentum before an event is ………. ……….. ……..
Is the same after an event
this is the conservation of momentum
Momentum formula in a triangle
M x V
What happens when a force acts on the object
It causes a change in momentum
A larger force means
A faster change in momentum and so a greater acceleration
E.g in a car crash if the momentum changes very quickly the forces on the body will be very large
What do brakes do
They do work against the kinetic energy in the car by :
- reducing the kinetic energy in the car by transferring it into heat and sound energy
What is a regenerative braking system
They are used in electric and hybrid cars they make use of energy instead of converting it to heat or sound
How do regenerative braking systems work
The brakes put the vehicles motor into reverse. With the motor going backwards the wheels are slowed down
At the same time the Motor acts as a electrical generator converting kinetic energy that is stored into chemical energy in the vehicles battery
Cars are designed to covert ……… ……….. ……… In a crash
Kinetic energy safely
What are crumple zones
The cars kinetic energy is converted into other forms of energy by the car body as it changes shape
- they increase the impact time decreasing the force produced by the change in momentum
What are side impact bars
They are strong metal tubes fitted into car door panels.
They help direct the kinetic energy of the crash away from the passengers
What are seat belts and what are they used for
Seat belts stretch slightly increasing time it takes for wearer (who’s wearing the seatbelt) to stop
This reduces the forces acting in the chest
Some of the energy is absorbed by the seatbelt stretching
What are air bags and what are they used for
These are also used to slow the passenger down gradually
And to prevent you from hitting hard surfaces in the car
What determines power rating on a car
( how fast it can go) there are 2
- Size and design of engines
2. If the car is aerodynamically designed ( if air flows easily and smoothly past it minimising air resistance)
How is static electricity caused
- It is caused by friction
- when certain insulating materials are rubbed together, negatively charged electrons will be scraped off and dumped on the other
- this will leave a positive static charge on one and a negative static charge on the other.
2 examples of static electricity
- With a polythene rod, electrons move from the duster to the rod
- with a acetate rod, electrons move from the rod to the duster
What are +VE and -VE charges produced electrostatic charges produced by ?
They are only ever produced by the movement of electrons.
Never the positive charges
What happens when 2 opposite electric charges are attracted to each other
They will attract
What happens when 2 of the same electric charges are together
They will repel
Electrical charges can move easily through what material ?
Metals because they are good conductors
What is current
Current is the flow of electric round a circuit
current will only flow if there is a potential difference
What is the unit for current
Ampere , A
What is potential difference
It is the driving force that pushes the current round
What is potential difference measured in
Volts, V
What is resistance
Resistance is anything in the circuit which slows the flow down.
What is the unit for resistance
Ohms, Ω
What happens if there is a great resistance
There is a small current that flows
What is the formula for current
Current = charge/time
What is the triangle formula for current
I x T
Q = charge I = current T= time
What is the formula for potential difference
P.D. = work done / charge
What is the triangle formula for potential difference
V x Q
W = work done V = potential difference Q = charge
A standard test circuit has ……..
3 things
- A ammeter must be place anywhere in the series
- But it must never be parallel like a voltmeter
- The voltmeter must be placed in parallel around the component under test. - not around the variable resistor or battery
What is Potential difference graph for different resistors
- The current through the resistor is directly proportional which means that there are different resistors have different resistances hence the different slopes
What is a potential difference graph with a filament light bulb
As the temperature of the filament increases the resistance increases hence the curve
What is a potential difference graph with a diode
Current will only flow through A diode in one direction. The diode has very high resistance in opposite directions
What does resistance increase with
Temperature
- when a electrical charge flows through a resistor, some of the electrical energy is transferred to heat energy and the resistor gets hot
What is the formula for potential difference
Potential difference = current x resistance
What is a diode
- A diode is a special material made from semiconductor materials such as silicone
- Current only flows one way in a diode
- It is used to regulate the potential difference in circuits
What is a light emitting diode
LED
Are used for lighting as they use much less current
Current flows through it in a forward direction
What is a light dependant resistor
LDR
Used for automatic night lights
They are dependant on intensity of light
What are the properties of a series circuit
- if you remove or disconnect one component the circuit breaks
- connected in lines end to end between +VE and -VE
- potential difference is shared ( voltage ) so voltage around a series circuit always add up
- current is the same everywhere
- resistance adds up
- cell voltages add up
What are the properties of a parallel circuit
- each component is separately connected to the +VE and -VE of the supply
- if a component is removed it will not effect circuit
- potential difference is the same all across all components
- current is shared between branches
- ammeters are always arranged in a series circuit
- voltmeter are always arranged in a parallel circuit
Examples of series circuits
Example of parallel circuits
- Christmas fairy lights ( series )
- Everything electrical in a car ( parallel )
Mains supply is ……..
Battery supply is ……..
Mains = a.c ( alternating currents ) Battery = d.c ( direct current )
What is the U.Ks mains supply
230 volts
Also UKs main supply is a.c
A.c mains supply is 50 cycles per second OR 50Hz
What is a cathode ray ossciliope
- A voltmeter
- on a.c supply
- the trace goes up and down with a regular pattern
- if you plug a d.c supply in. You will just get a straight line
What is the formula for frequency
Frequency = 1 / time period
How do you measure the time period on a oscilliope trace
Measure the horizontal distance between the two peaks
Name 6 electrical hazards in the home
- Long cables
- Frayed cables
- Cables in contact of something hot or wet
- Water near sockets
- Shoving things into sockets
- Damaged plugs
What are the 3 separate wires on the cable
Brown live wire:
- supplies alternates between +VE and -VE voltage
Blue neutral wire:
- is always at OV electricity flows normally flows in and out through the live and neutral wire only.
Green and yellow earth wire:
- used for protecting the wiring for safety
- works with fuse to prevent fire and shocks
- carries electricity to the earth and away from you if live or neutral wire touches metal
What are the safety features of the plug
- The metal parts are made of copper or brass because they are good conductors
- The case and cables are made of rubber and plastic because they are good insulators
How do earths and fuses prevent electrical over loads
- If a fault develops in which the live wire touches the metal. The metal is earthed so it will send the current to the earth.
- The surge in the current melts the fuse causing the circuit to break
- Fuses should be rated as high as possible for safety
What does insulating materials make appliances
Double insulated
(this is because all cables are already in metal cases and earthed. If It has a plastic case and no metal showing it will make it double insulated)
Advantages of circuit breakers
- when circuit breakers detect a surge in current in circuit, they break the circuit by opening a switch ( however are more expensive )
- can be easily reset by flicking a switch - more convenient than fuses
Which have to be replaced after melting
What is a residual current circuit breaker
( RCCBs) and its advantages
- operate faster than a fuse
- when it detects a difference in a current it quickly cuts off the power
- can detect small current changes
Anything which supplies electricity supplies …………
Energy
So cells , batteries and generators all transfer energy
What do all resistors produce when a current flows through it
Heat
When a current flows through any electrical resistor. Then electrical energy is converted to heat energy
What is meant if a appliance is ‘efficient’
It wastes less energy
These appliances transfer more of their total electrical energy output to useful energy.
- however they do cost more, but will pay you back over time with the money you save
What is the formula for energy transferred
Energy transferred = power x time
- the total energy transferred by an appliance depends on how long the appliance is on and it’s power . The power is the energy that it uses per second
What is the formula for electrical power
Power = current x potential difference
OR triangle formula which is
P ---------- I x v
What is the formula for energy transferred
Energy transferred = charge x potential difference
OR triangle formula
E
-------
Q x VWhat does a bigger change in p.d mean
- more energy transferred
- battery will be bigger with a bigger voltage for more energy
Number of protons are equal to the number of ………..
Electrons
What was the plum pudding theory
- Atoms were spheres with positive charges
- with tiny negative electrons stuck in them like plums in a pudding
What did the two scientist which came up with the plum pudding theory would happen if they fired positive alpha particles into gold foil
- they expected the positively charged alpha particles would be slightly deflected.
- however most of the alpha particles went straight through and the odd one came back
- this meant that most of the mass was concentrated at the centre
in the tiny nucleus - it also showed that a tom is mostly empty space
What is a isotope
- Different forms of the same element
- they have the same number of protons but different number of neutrons
Where does background radiation come form
- Cosmic rays
- Man made sources e.g nuclear weapons and tests
- air, food and environment
Why is being in high altitudes increase amount of radiation
Because there is more exposure to cosmic rays
Why is being underground have a increase amount of radiation
It increases because of rocks all around
What are alpha particles
Helium nuclei
- 2 neutrons and 2 protons
- relatively big and slow moving
What are beta particles
Electrons
- quite fast and small
- penetrate moderately into material
What are gamma rays
Very short wave lengths - EM waves
- penetrate far into materials
- pass straight through air
Alpha particles and beta particles are deflected by what ?
Magnetic fields
This is because alpha particles are positive and beta particles are negative, so when they travel through a magnetic field they will be deflected because of opposite charges
What is a half life
Is the average time it takes for the number of nuclei in a radioactive isotope sample to halve
What are the uses of alpha particles
Smoke detectors:
- a weak source of alpha particles are placed into smoke detectors
- close to 2 electrodes
- the source causes ionisation and a current flows between electrodes.
What are the uses of beta and gamma
Tracers in medicine
2 uses of gamma rays
Radiotherapy - to treat cancer and kill cancer cells
Sterilisation of food and surgical instruments
How does radiation damage living cells
- they can collide with molecules which can destroy or damage molecules
- which can cause mutant cells which is cancer
Why is radiation good for the body
They can kill cancer cells
Why are beta and gamma rays dangerous outside the body
Because they can penetrate through skin and damage delicate organs
Why are alpha particles dangerous inside the body
Because they damage a very localised area
Whilst gamma and beta normally pass straight through
What are the safety precautions for holding radioactive materials
- Only use for short time so you are not exposed for too long
- Never allow skin contact
- Store in lead boxes as lead absorbs radiatio
What is the life cycle of a star if it is the same size as the sun
- Stars initially form from dust and gas
- They spiral together to become a protostar
- The star goes through a stable period at this point due to balanced forces
- Soon forces become unbalanced and gases run out, so the star swells up into a red giant (same size of the sun )
- Which will then become a white dwarf and eventually a black dwarf
What is nuclear fission
The splitting of a neutron into 2 or more pieces
What is the life cycle of a star if it is bigger than the sun
- Stars initially form from dust and gas
- They spiral together to become a protostar
- The star goes through a stable period at this point due to balanced forces
- Soon forces become unbalanced and gases disappear, so the star swells up into a red SUPER giant
- big stars become a supernova as they undergo more fusion and expand
- They become a neutron star and when big enough this will turn into a black hole
