PHYSICS PART 1 and 2 Flashcards
What is velocity?
When something has both speed and direction
m/s or km/h or mph
What is acceleration?
A change in velocity
m/s^2
What is speed?
How fast you’re going with no regard to direction
m/s or km/h or mph
What is force?
A push or pull that changes the way an object is moving or is shaped
(newtons)
What is mass?
The amount of matter in an object
Kilograms
What can reduce the acceleration for a particular force?
A greater/larger mass of an object
In distance time graphs, what does the gradient suggest?
The speed
In a distance time graph, what do flat sections suggest?
It is stationary and has stopped
In a distance time graphs, what does a straight uphill/downhill line suggest?
It is travelling at a steady speed
In a distance time graph, the steeper the graph…
The faster it’s going
In a distance time graph, what do downhill sections suggest?
It is returning to its starting point
What do curves suggest on a distance time graph?
Acceleration or deceleration
What does an increasing gradient (steepening curve) suggest?
It’s speeding up
What does a decreasing gradient (levelling off curve) suggest?
It slowing down
Distance formula
Distance (m)
Speed (m/s)
MULTIPLIED BY
Time (s)
(Rearrange for speed and time)
What can a change in velocity suggest?
A change in speed, direction, or BOTH
Acceleration formula
Acceleration (m/s^2)
Change in velocity (speed) (m/s)
DIVIDED BY
Time taken (s)
What does the gradient in a velocity time graph suggest?
Acceleration
What does a flat section suggest in a velocity time graph?
Steady speed
In a velocity time graph, the steeper the graph…
The greater the acceleration of deceleration
In a velocity time graph, what do uphill sections suggest? (/)
Acceleration
In a velocity time graph, what do downhill sections suggest? ()
Deceleration
What does a curve in a velocity time graph suggest?
A change in acceleration
What does the area under any section of a velocity time graph suggest?
The distance travelled in that time interval
How can the velocity be given for a given time on a velocity time graph
Reading of the value off the correct axis
Gravitational force is the force between all…
Masses
What are the effects of gravity attracting masses?(2)
- It makes all things accelerate towards the ground with the same acceleration
- It gives everything a weight
What is weight?
The force of gravity pulling something towards the centre of the earth
(newtons)
How is weight measured?
Spring balance or newton metre
How is mass measured?
Using a mass balance
Weight formula
Weight (newtons)
Mass (kg)
MULTIPLIED BY
Gravitational field strength (N/kg)
What is the gravitational field strength on Earth?
Roughly 10 N/kg
What is the gravitational field strength on the Moon?
Roughly 1.6 N/kg
What is the resultant force?
The overall force on a point it on an object
The overall effect of forces, can decide what about the motion of an object? (3)
Whether it will:
- Accelerate
- Decelerate
- Stay at a steady speed
How can the resultant force be found if both forces work in the same direction?
You add them:
ForceX + ForceY= Resultant Force
How can the resultant force be found if both forces are working in opposite directions?
You subtract them:
ForceX - ForceY = Resultant Force
What can be suggested if the resultant force is 0? (2)
- a stationary object remains stationary
- a moving object continues at the same velocity
If a resultant force is acting upon an object it causes a…
Change in the objects velocity
When answering questions about resultant forces what should always be included in your answer?
The direction that the forces are pointing to
E.g 400N to the left in a positive direction
Who worked out the laws of motion?
Sir Isaac Newton
What are the laws of motion? (3)
- an object needs a force to start moving
- no resultant force means no change in velocity
- a resultant force means acceleration
If there is a non zero resultant force, what happens to the motion of the object?
It will accelerate in the direction of the force
A non zero resultant force always results in…
Acceleration or deceleration
The acceleration produced by a non zero resultant force can lead to…(5)
- Starting
- Stopping
- Speeding up
- Slowing down
- Changing direction
Why do we need a driving force to keep us travelling at a steady speed?
Because of air resistance and friction
Resultant force formula
Resultant force (newtons, N)
Mass (kg)
MULTIPLIED BY
Acceleration (m/s^2)
When two objects interact, the forces they exert on each other are…
Equal and opposite
If forces are always equal when 2 objects interact, how does anything move?
The forces are opposite and a different mass can cause one object to accelerate away faster (and in the opposite direction)
What effect does friction have on an object that has no force propelling on it?
It will always slow down and eventually stop (except in space)
Friction acts in which direction?
Opposite direction to the movement
To travel at a steady speed, the frictional force must…
Balance the driving force
When do you get friction? (2)
When two surfaces become in contact
When an object passes through a fluid (drag)
Most resistive forces are caused by…
Air resistance or drag
How can you reduce drag in fluids?
Keeping the shape of the object streamlined
An example of when the drag force is very high
Parachute
Drag increases as…
Speed increases
How do forces affect a parachutist?
- When they first set off, gravity is larger than than air resistance do they accelerate
- As the speed increases so does the air resistance and therefore the acceleration reduces
- The forces then become balanced and a terminal velocity is reached and will no longer accelerate, it will just fall at a slower steady speed
All objects flowing through … reach a terminal velocity
Fluids
The terminal velocity of falling objects depends on their…(2)
Shape and area
On earth, why do things fall to the ground at different speeds?
Because air resistance acts on all objects different
Define total stopping distance
The distance covered in the time between the driver first spotting a hazard and the vehicle coming to a complete stop
Define stopping distance
The sum of the thinking and braking distance
Define reaction time
The time between the driver spotting a hazard and taking action
Define thinking distance
The distance the vehicle tracked during the drivers reaction time
What is thinking distance affected by? (2)
- how fast you’re going
- how dopey you are
(tiredness, alcohol, drugs, careless attitude)
What is braking distance affected by? (4)
- how fast your going
- how good your breaks are
- how good the tyres are (min tread depth of 1.6mm)
- how good the grip is (this depends on:)
road surface, weather conditions and tyres
What is work done/energy transferred?
When a force moves an object through a distance
joules
Work done formula
Work done (joules)
Force (newtons, N)
MULTIPLIED BY
Distance (m)
What is gravitational potential energy?
The energy an object has because if its vertical position in a gravitational field
(Joules)
Gravitational potential energy formula
Gravitational potential energy (j) = Mass (kg) MULTIPLIED BY Gravitational field strength (N/kg) MULTIPLIED BY Height (m)
What is kinetic energy?
The energy of movement
Joules
Kinetic energy formula
Kinetic energy (joules) = 1/2 MULTIPLIED BY Mass (kg) MULTIPLIED BY Speed^2 (m/s)
The kinetic energy of something depends on…(2)
Mass and speed, the faster/bigger these are the higher the kinetic energy will be
Kinetic energy transferred is what?
Work done (Joules)
Kinetic energy transferred formula
Kinetic energy transferred (j) = Work done by brakes (j) Or 1/2(mass)x(speed^2)=max braking force(N)x braking distance(N)
Conservation of energy
Energy can never be created or destroyed, only converted into different forms
Potential energy lost means…
Kinetic energy is gained
Why do meteors never completely hit the earth?
They have very high kinetic energy
Friction (due to collisions) causes some of the energy to transfer into heat and sound
The temperature become so extreme that most meteors burn up and so never hit the ground
What is elastic potential energy?
When work is done to an object to change its shape, the energy is not lost but stored as elastic potential energy.
It then is converted back into kinetic energy where the force is done and as a result for e.g an elastic band bounces back
The extension of an elastic object is … to the force
Directly proportional
Force formula
Force (N)
Spring constant (N/m)
MULTIPLIED BY
Extension (m)
What is the limit of proportionality?
The maximum force that the elastic object can take and still extend proportionally
What is power?
The rate of energy transferred
Watts or j/s
Power formula
Power (Watts or j/s)
Work done/energy transferred (j)
DIVIDED BY
Time taken (s)
One watt is equal to…
1 joule of energy transferred per second
How can you calculate the power output of a person? (2)
- The timed run upstairs
- The time acceleration
(Must repeat these experiments and calculate an average for accurate results)
What is momentum?
Properly of moving objects
It has a size and direction (but not speed)
(Kg m/s)
Momentum formula
Momentum (kg m/s)
Mass (kg)
MULTIPLIED BY
Velocity (m/s)
An object has a higher momentum if it has…(2)
A greater mass of an object
A greater velocity
Conservation of momentum
Momentum before = momentum after
When a force acts on an object it causes a…
Change in momentum
A larger force acting on an object causes a…
Faster change of momentum (and so greater acceleration)
How do breaks reduce kinetic energy?
Work is done when the breaks are applied
Brakes transfer energy into heat and sound
What are regenerative brakes?
Use the system that drives the vehicle to do most of the braking
They store energy of braking instead of wasting it
It causes the motor to run backwards so the wheels are slowed down
How do crumple zones lessen the force on passengers during a crash?
At the front and back, they crumple on impact
Kinetic energy is converted to other forms as the car body changed shape
They increase the impact time, decreasing the force produced
How do side impact bars reduce force on passengers during a crash?
They direct kinetic energy away from passengers to areas such as crumple zones
How can seat belts reduce forces on passengers during a crash?
They stretch causing an increase in time
This reduces the forces acting on the chest
Some kinetic energy is absorbed by the belt stretching
How do air bags reduce forces felt by passengers in a crash?
They slow you down more gradually
Stop you from hitting hard surfaces
What determines how powerful a car is? (2)
Size of car engine
Design of car engine
What is static electricity?
Charges that are not free to move e.g. In insulating materials
How are electric shocks caused?
If the charges are not free to move they can build up in one area which often results in a shock when they eventually do move
How can an insulting materials charge change?
When certain insulating materials get rubbed together the (negatively charged) electrons are rubbed off and moved onto the other material
This makes it gain a positive static charge and the other gain a negative static charge
Example of static charge experiment
Polythene and acetate rod with cloth
Polythene rod - rod loses electrons and becomes positively charged, the cloth gains electrons and is now negatively charged
Acetate rod - rod gains electrons and becomes negatively charged, cloth loses electrons and becomes positively charged
Like charges…
Repel
Opposite charges…
Attract
Electrical charges can move easily though materials called…
Conductors e.g. Metals
What is current?
The flow of electric charge around a circuit, current only flows if there is a voltage
(Ampere, A)
What is voltage/ potential difference?
The driving force that pushes the current around
Volts, V
What is resistance?
Anything that slows the flow in the circuit down
Ohms
The greater the resistance for a given voltage…
The smaller the current
Total charge though a circuit depends on… (2)
Current and time
Current formula
Current (A)
Charge (Coulombs, C)
DIVIDED BY
Time (seconds)
Potential difference formula
Voltage (Volts)
Work done (joules)
DIVIDED BY
Charge (Amperes)
What does the “standard test circuit” allow you to find out?
The resistance of a component
The ammeter (3)
- Measures the current (amps)
- Placed in series
- Can be placed anywhere, except in parallel
Voltmeter (2)
- Measures voltage (volts)
2. Placed in parallel around component NOT variable resistor or battery
5 key points about the “standard test circuit”
- Used to test components and create V-I graphs
- Component, ammeter and variable register are in series and therefore any order. Voltmeter only in parallel around component.
- Varying the variable resistor alters current
- You can take several readings from the ammeter and voltmeter
- Plotting the value for current and voltage on a V-I graph allows you to going the resistance
Electrons move wrong circuits from…
-ve to +ve
What do V-I graphs show you?
How the current varies as you change the voltage
What 3 V-I graphs should you know?
- Different resistors
- Filament lamp
- Diode/LED
What does the “Different Resistors” V-I graph show?
(Straight diagonal line)
The current through a resistor is DIRECTLY PROPORTIONAL to the voltage.
Differ resistors have different resistances
What does the “Filament lamp” B-I graph show?
(S shaped curve)
As the temperature increases, the resistance increases
As temp increases particles in the metal gain more energy and vibrate, making it harder for electrons to flow (so resistance increases)
What does the “Diode/LED” V-I graph show?
Current will only flow in one direction, in a forward direction
Little current flows in the opposite direction so the resistance in the opposite direction is very high
Resistance increases with…
Temperature
Who does an increase in temperature increase the resistance?
When a charge flows, energy can be transferred to heat which makes the resistor heat up
The ions then vibrate more making it hard for the charge carrying electrons to get through the resistor
Why is there a limit to the amount of current that can flow in resistors?
More current means an increase in temperature
This means an increase in resistance
Therefore the current decreases again
(This causes the graph for the filament lamp to level off at high currents)
Voltage formula
Potential difference (volts, v)
Current (amps, a)
MULTIPLIED BY
Resistance (ohms)
Diode features (4)
- Special device made from a semi conductor material (such as silicon)
- Regulates the voltage in circuits
- Allows current to flow in only one direction
- Useful in electronic circuits
LED(Light emitting diode) features (4)
- emits light when current flows through it in a forward direction
- uses a smaller current than most forms of lighting so are quite common
- indicate the presence of a current (e.g. Used in TVs to show they are switched on)
- also used for numbers on digital clocks, traffic lights and remote controls
LDR(light dependent resistor) features (4)
- dependent on the intensity of light
- in bright light, the resistance falls
- in darkness, the resistance is highest
- uses include automatic night lights, outdoor lighting and burglar detectors
Thermistor features (4)
- temperature dependant resistor
- when hot, the resistance falls
- when cold, the resistance increases
- uses as temperature detectors (e.g. car engine temperature sensors and electronic thermostats)
Series circuits RULES (5)
- Removing a component breaks the circuit, everything stops
- Voltage is shared
(total voltage = V 1+ V2…) - Current is the same everywhere (A1=A2)
- Resistance adds up (R = R1 + R2)
- Cell voltages add up
Parallel circuits RULES
- Each component is connecting separately, removing one will not affect the others
- Voltage is the same (V1 = V2 = V3)
- Current is shared (A = A1 + A2)
- The total current entering a junction is equal to the total current leaving
- Ammeters are an exception and are connected in series even if the circuit is parallel
Mains voltage is…
230 Volts
Example of when series circuits are used
Christmas fairy lights
Parallel connection is essential in a car to give which features? (2)
- everything can be turned on and off separately
- everything always gets the full voltage from the battery
Why do alternating currents work?
Because to transfer energy, it doesn’t matter which way the charge carriers are going
What is the UK mains supply?
Approx. 230 Volts
What is an AC supply?
Alternating current
The current is constantly changing direction
What is the frequency of the AC mains supply?
50 cycles per second
Or 50 Hertz
What is DC?
Direct current, supplied by cells and batteries
Current always flows in the same direction
How can electricity supplies be seen?
On an oscilloscope screen
What is a cathode ray oscilloscope? (CRO)
Similar to a voltmeter
Voltage for AC supply in an oscilloscope
If you plug an AC supply into the oscilloscope
-A trace appears on the screen that shows how the voltage changes with time
(The pattern is regular)
( looks like a wave)
What does the trace look like when you plug a DC supply into an oscilloscope?
A straight line
The vertical height of the AC trace at any point shows…
The input voltage
Measure the height to find voltage
How do you find the voltage for DC?
The distance from the straight line trace to the centre line
What does the gain dial do?
Controls how many volts each cm division represents on the vertical axis
What does the timebase dial control?
How many milliseconds each division represents on the horizontal axis (1ms=0.001s)
What is a time period?
The time to complete one cycle (a whole wave)
X axis on the oscilloscope is
Time
Y axis on the oscilloscope is
Voltage
Frequency formula
Frequency (Hz) = 1 DIVIDED BY Time period (seconds)
Mains supply is
AC
Battery supply is
DC
AC’s current can be increased/decreased using a
Transformer
The lower the current in power transmission lines
The less energy is wasted (as heat)
Hazards in the home (9)
- Long cables
- Frayed cables
- Cables touching something hot/wet
- Water near sockets
- Shoving items into sockets
- Damaged plugs
- Too many plugs in one socket
- Lighting sockets without bulbs
- Appliances with no covers in
What does the Earth Pin do?
Connects to Earth wire
Transfers energy away from device if there is a fault
What does the neutral pin do?
Connects to the neutral wire
Completes the circuit
Voltage of 0
What does the live pin do?
Connects to live wire
Provides the energy to the device
Voltage of 230V
Earth wire
Protects the wiring
For safety
Works with a fuse to prevent shocks/fires
Electricity flows normally through which wires?
Live and neutral only
Live wire
Alternates between a positive and negative voltage
Each wire has…
A core of copper
A coloured plastic covering
Most cables have … wires
3
The separate wires are called
The Earth wire (green and yellow)
The Neutral wire (blue)
The Live wire (brown)
Safety features of wiring inside a plug and cable (4)
- the correct wire must be tightly screwed to the correct pin
- no bare wires should be shown inside the plug
- the cable grip must be tightly fastened over the cable outer layer
- thicker cables have less resistance and carry more current
Why are the metal parts of the plug made it brass or copper?
Good conductors
Why is the case, case grip/ insulation made of rubber or plastic?
Good insulators
Flexible
Earthing and fuses prevent…
Electrical overloads
How does the Earth wire along with a fuse/circuit breaker work?
- if a fault eg live wire touches metal casing, then too big a current flows though live wire, case and out down the Earth wire because the case is heavily earthed
- this melts the fuse as it goes beyond the fuse rating so the circuit gets broken
- this makes it impossible to get an electric shock and prevents the risk of a fire
Why does the fuse rating increase with cable thickness?
The larger the current, the thicker the cable you need to carry it
Define earthing
The case must be attached to an Earth wire
Why are appliances with metal cases earthed?
To reduce the risk of an electric shock
An earthed wire can never…
Become live
When is an appliance double insulated?
If it has a plastic casing with no metal showing
Anything that is double insulated doesn’t require a … wire
Earth
What are circuit breakers?
Electrical safety devices used in circuits to protect it if too much current flows
Advantages of circuit breakers over fuses
They can be reset by flicking the switch (instead of being replaced)
They are quicker
Advantages of fuses over circuit breakers
They are much cheaper
Name a type of circuit breaker
Residual Current Circuit Breaker (RCCBs)
Explain how RCCBs work
Detects a difference in current and cuts of power by opening a switch
Much faster than fuses
Time is not wasted on melting fuses so it’s safer
Work for small current changes
Effective
ALL Resistors produce … when a … flows through them
Heat, current
Why do resistors produce heat when a current flows through them?
Electrical energy is converted to heat energy
Filament bulbs
Works by passing a current through a thin wire and heating it up so it glows
It therefore wastes a lot of energy as heat
If an appliance is efficient…
It wastes less energy
How can you make sure as little energy is wasted on heat?
Buy energy efficient electrical appliances
Energy transferred formula
Energy transferred (J)
Power (w)
MULTIPLIED BY
Time (seconds)
Electrical power formula
Power (w)
Current (a)
MULTIPLIED BY
Voltage (v)
Fuse needed formula
Fuse (a)
Power (w)
DIVIDED BY
Voltage (v)
Energy transformed formula
Energy transformed (j) = Electrical charge (c)
MULTIPLIED BY
Voltage (v)
The bigger the change in voltage, the … energy is transferred for a given amount of charge
More
Why did the plum pudding experiment take place in a vacuum chamber?
So the alpha particles do not bounce or come into contact with the air particles
What was the plum pudding experiment?
Alpha particles were fired onto a thin gold foil in the expectancy they would be slightly deflected by the electrons
