Our Dynamic Universe Flashcards
Prefixes
pico, p, x10^-12
nano, n, x10^-9
micro, u, x10^-6
milli, m, x10^-3
centi, c, 10^-2
kilo, k, x10^3
mega, M, x10^6
giga, G, x10^9
tera, T, x10^12
What is an uncertainty?
The measurement of any physical quantity is liable to an error or uncertainty
What is a systematic uncertainty and what are examples on how they are caused?
These are cause by some constant value.
It is an error which affects all the measurements the same way.
E.g. Scale not properly set to 0, measuring tape ‘stretched’, or faulty apparatus (zero on ruler scale isn’t at the edge)
What is a reading uncertainty and how do you calculate them?
This indicates how well and instrument scale can be read.
For analogue scales, uncertainty is +/-half of the least significant digit.
For digital scales, uncertainty is +/- 1 in the least significant digit.
What is a random uncertainty?
These show up when you make a series of measurements of the same quantity, when the measurement is repeated and slight variations occur.
Random uncertainty’s may be reduced by increasing the number of repeated measurements.
Small uncertainty = more reliable
What is a percentage uncertainty and how do you calculate them?
Allows us to indicate how precise a value is.
% = random uncertainty/mean value x 100%
The overall uncertainty will be the highest percentage uncertainty.
What does ‘motion’ mean?
The word motion is used to describe something that is moving.
What is the definition of speed?
The distance travelled by an object in one second.
What is average speed and experiment?
Average speed is the average speed throughout the whole journey. You need two pieces of information; total distance travelled and time for total journey.
You need a QED timer, metre stick, light gates, cart and mask.
Allow for the trolley to run down the slope, measure the difference between the two light gates using a metre stick to get the distance. Record the time for the trolley to run between light gates on the QED timer and sub into formula to get the average speed.
What is instantaneous speed and experiment?
The instantaneous speed is the speed of an object at a particular point on the journey.
You need a ruler, a cart and mask, a light gate and a QED timer.
Let the trolley run down the slope and the timer will start recording when the mask cuts the light beam and stops once the light beam is restored. Use the length of the mask and time to travel through the light gate to get instantaneous speed.
The smaller the time interval, the more accurate the value of instantaneous speed.
What is acceleration and experiment?
Acceleration is the change is velocity per unit time.
Acceleration is directly proportional to force.
Acceleration of any object is in the same direction as the unbalanced force acting on it.
SINGLE CARD, DOUBLE BEAM EXPERIMENT (state apparatus)
- measure the length of the mask.
- QED timer records the time for the mask to pass the first light gate
- QED timer record the time for the mask to pass the second light gate.
- QED timer record the time to move inbetween the light gates.
initial velocity = length of card/t1
final velocity = length of card/t1
(use acceleration formula)
DOUBLE CARD, SINGLE BEAM
- QED timer record time for the first mask to pass the light gate.
- QED timer records time for the second mask to pass the light gate.
- QED timer records time between passing the two masks passing through the light gate.
(use same three formulas as before)
If an object is slowing down, the acceleration will be negative = deceleration.
When the acceleration is vertical, a=9.8ms^-2 due to gravity which acts downwards.
What’s the speed/time graph formula?
D= AreaUnderGraph
What are vectors and scalars and what are examples of them?
A scalar quantity is defined by magnitude.
A vector quantity is defined by magnitude and direction.
VECTORS
- Displacement
- Acceleration
- Impulse
- Force
- Weight
- Momentum
- Velocity
SCALARS
- Pressue
- Power
- Volume
- Distance
- Work
- Mass
- Speed
- Kinetic energy
- Potential energy
- Temperature
Addition of vectors
Two or more vectors can be added to get a resultant vector.
Magnitude and direction need to be taken into account.
Pythagoras, SOHCAHTOA, Sine rule, and cosine rule can be used to solve these.
Pythagoras: c^2 = a^2 +b^2
SOHCAHTOA
Sine rule: Can be used if cosine can’t be used, a/sinA = b/sinB = c/sinC
Cosine rule: Can be used if you have all 3 sides of a triangle, or if you have two sides and an angle al next to each other, a^2 = b^2 + c^2 -2bccosA
What is velocity?
The rate of change of displacement.
The speed of something in a given direction.
What is displacement and distance?
Displacement (vector) - The direct length from start to finish.
Distance (scalar) - The total path length.
Velocity/time graph formula
s=AreaUnderGraph
Bouncing ball example
- When a ball is bouncing, it constantly changes direction.
- As it moves upwards it has a high initial velocity that slows down to 0 as it reaches maximum height.
- As it travels back down, it starts at 0 but accelerates due to gravity until it hits the ground and changes direction again.
- A v/t graph for a bouncing ball shows motion both above and below the horizontal axis to show the content change in direction.
(Above the horizontal axis = moving upwards)
What is a projectile?
When a projectile is fired, it takes a curved path.
The motion of projectiles consist of two independent components:
- constant horizontal velocity (a=0)
- constant vertical acceleration (caused by gravitational pull).
The vertical velocity t maximum height is 0.
The time taken to reach maximum height from a surface is equal to the time to return from maximum height back to the surface. The time to reach maximum height is half of the total time taken.
Horizontal and vertical velocity components
Vh = vcos(theta)
Vv = vsin(theta)
What is Newton’s first law?
An object will remain stationery or at constant velocity unless acted upon by an unbalanced force.
What is Newton’s second law?
For a change in motion to occur, forces must be involved. This is the idea of acceleration.
What is Newton’s third law?
Is A exerts a force on B, B will exert an equal but opposite force on A.
What is resolution?
Any vector can be resolved into two components at right angles to each other.
Force component calculations
Fh = Fcos(theta)
Fv = Fsin(theta)
What is the resultant number of forces?
A single force which will have the same effect as all the other forces.
Experiment to compare the resultant of two forces
Apparatus: 2 newton balances, elastic bands, one wooden board, white paper and drawing pin
- set up apparatus
- With the elastic pulled to a point, more the values of F1, F2 and trace their direction on paper. Mark the point on the paper.
- Using one spring balance, pull the elastic until the point is reached and note the value required Ft.
- Now combine F1 and F2 with the value of Ft.
What are the forces of weight acting on a slope and how do you calculate them?
If an object is on a slope, its weight acts vertically downwards. The weight can be split into two components at right angles to each other.
Component of weight acting down slope: F = mgsin(theta)
Component of weight perpendicular to slope: F = mgcos(theta)
What is Terminal velocity?
When an object falls towards the earth, it has two vertical forces acting on it, air resistance and weight.
As the object falls, the velocity increases due to the acceleration of gravity.
As the speed increases, so does the air resistance.
Eventually, the two forces will even out and the object will no longer accelerate (balanced forces = constant velocity). This is terminal velocity.
Idea of a parachute
When doing a parachute jump, the parachute is released to increase the surface area and as a result the air resistance increases which slows down the parachute’s to allow them to land safely.
Lift problems
In all lift problems, there will always be a tension in the cable supporting it and a weight, w=mg.
R = reaction force exerted on person by floor = tension
LIFT ACCELERATING UPWARDS
R = m x a - (-w)
LIFT DECELERATES UPWARDS
R = m x (-a) - (-w)
LIFT ACCELERATES DOWNWARDS
R = m x -(a) - (-w)
LIFT DECELERATES DOWNWARDS
R = m x a - (-w)
If the lift is at rest or constant speed, tension = weight
Conservation of energy (What is work done, gravitational potential and kinetic energy?)
Work is done when a force is used to move the objects to a certain distance (energy transfer).
Power is measured in watts (the rate of doing work).
Gravitational potential energy is the energy that an object has due to its position in a force field.
Kinetic energy is the energy possessed due to motion. This is the amount of energy needed to get the object to its travelling velocity and the same amount of energy is required to bring it to rest.
Acceleration causes and increase in kinetic energy.
Energy is measured in joules
The total energy of any closed system is conserved, although the energy may change its form. Energy can’t be created or destroyed.
Using Ep and Ek to find ‘v’
v = /2gh
What is momentum?
Momentum is the measure of the velocity and mass of a moving object.
Elastic collisions, Inelastic collisions, Explosions - Is kinetic energy and momentum conserved?
An elastic collision is when both kinetic energy and momentum are conserved.
An inelastic collision is one where only momentum is conserved. (objects may stick together) (kinetic energy changes to heat and sound so it isn’t conserved).
In an explosion, only momentum is conserved (kinetic energy after is greater than before).
What is impulse and what is it measured in?
An object is accelerated by a force, for a time.
The unbalanced force is given by:
mv-mu/t. ( = impulse)
Impulse = change in momentum
Impulse = force x time
Impulse is measured in Ns.
How to improve experimental results
Repeat readings and use meters with smaller divisions.
Cosine rule and Sine rule
a^ = b^ + c^ - 2bccosA
(use cosine rule when you have 2 sides and an angle or all three sides)
a/sinA = b/sinB = c/sinC
Graphs of motion
CONSTANT VELOCITY GRAPH
- constant increasing displacement
- constant velocity
- constant acceleration = 0
COSTANT ACCELERATION GRAPH
- increasingly increasing displacement
- constant increasing velocity
- constant acceleration
CONSTANT DECELERATION GRAPHS
- decreasingly decreasing displacement
- constants decreasing velocity
- constant deceleration
What is friction?
Friction always acts against the direction of motion (opposes motion). When the applied force and friction is balanced, Newton’s first law tells us that the objects will remain at constant velocity.
What type of force does friction represent?
A negative vector quantity
What factors increase frictional force?
- Velocity
- Surface area
- Contact pressure between surfaces
What are some components of friction force acting on a car?
- Air resistance
- Friction in the wheel bearings
- Resistance between the tyres and the road
What happens to a mass released at a distance from the Earth?
It experiences a force in the direction towards the Earth.
This force is due to the gravitational field created by the Earth.
What is a gravitational field?
A region where a mass experiences a force due to gravity.
They can be illustrated using lines with arrows indicating strength and direction.
How is gravitational field strength defined?
It is a measure of the force on a unit mass.
Expressed in units of N/kg.
What is the value of gravitational field strength on Earth?
g = 9.8 ± 0.05 N/kg.
This value is considered constant for most practical purposes on Earth’s surface.
Newtons thought experiment
Isaac Newton studied the effect of gravity on projectiles.
He arrived at his famous thought experiment. Imagine a cannonball fired horizontally. The ball has a constant horizontal velocity but also a constant vertical acceleration which brings it down to the ground. Now Newton imagined what would happen if the ball could be fired with a greater height and greater horizontal speed. The
ball will travel further each time but the curvature of the Earth will start to be noticed. Although the ball is always accelerating towards the ground, due to gravity, a point will come when the ball will never reach the ground but be in orbit around the Earth.
If there was no gravity the ball would travel in a straight line out into space.
The path without gravity is obeying Newton’s 1st law of motion.
The path with gravity is obeying Newton’s 2nd law of motion.
What is a satellite and how do they work? What is an example of a natural satellite?
A satellite is an objects that orbits around another object. Satellites are in free fall around an object.
Satellites are constantly falling towards the Earth because they have a great enough horizontal speed. They don’t move off into space because there is a force of gravity towards the Earth.
A satellite has a constantly changing velocity whilst the distance is also constantly changing which means that a satellite can be accelerating when it has a constant speed.
A natural satellite would be the Moon orbiting the Earth.
True or false: The speed of light in a vacuum is the same for all observers
True
What is the definition of mass?
How much matter is in an object and is measured in kg
What is the definition of weight?
The force of gravity acting on an object measured in N.
True or false: The smaller the mass, the bigger the gravitational pull.
False - The bigger the mass, the bigger the gravitational pull.
How were stars believed to be formed?
Scientists believe that stars were formed by the gravitational pull between hydrogen molecules in space.
This attraction built up over time to a large enough mass of gas that the forces at the centre were so big that it caused the hydrogen molecules to fuse together, generating energy. (the centre of the sun).
This energy radiating outwards counteracts the gravitational force moving trying to compress the sun inwards.
Eventually the hydrogen will be used up and the sun will collapse under its own gravity in about 4 billion years time.
How were planets believed to be formed?
Once a star is formed, there will be debris orbiting around it.
This debris might join together to form planets, again due to the gravitational attraction between particles.
This is the most common explanation to explain the formation of our solar systems.
What is the ‘slingshot’ method when launching a spacecraft?
A spacecraft is sent close to a planet, where it accelerates due to its gravitational field.
If the trajectory is right then the craft will speed past the planet with an increased speed. If not, the spacecraft will crash into the planet.
Apollo 13 used this method when returning to Earth.
True or false: Zero gravity is bad for human health as it causes huge muscle wastage.
True
What is Newtons Inverse Square Law of gravitation?
There is a force of attraction between any two objects in the Universe.
(The size of the force is proportional to the produce of the masses of the two objects, and inversely proportional to the square of the distance between them.)
True or false: The speed of light in a vacuum is different for all observers.
False - The speed of light in a vacuum is the same for all observers.
What is special relativity?
Special relativity describes the behaviour of objects travelling at a very high speeds. It is ‘special’ because it is the special case when the motion between observers is uniform.
What is time dilation?
The increase in time of an object moving relative to an observer.
The stationary observer will record a greater time than the moving observer for the same journey travelling at speeds close to the speed of light.
What is the difference between t’ and t?
t’ - Time reference for the stationery observer.
t - Time reference for the moving observer.
What is the evidence to support Einstein’s theory on time dilation?
There is a partial called a muon that is created in the upper atmosphere. They have a half life of 1.56x10^-6s and only exist for a short time. This means for every million muons created at a height of 10km, only 3 should reach the Earth. But 5000 are actually detected because the ‘muon clock’ runs slower compared to the observer on Earth.
Potential answer: (For an observer on Earth’s frame of reference the mean life of the muon is much greater).
What is length contraction?
The decrease in length of an object moving relative to an observer.
What is the difference between l’ and l?
l’ - length for the stationary observer.
l - length for the moving observer.
True or false: When moving at velocities close to the speed of light, for the stationary observer, time is longer and length is shorter.
True
What is the lorentz factor?
The Lorentz factor is a quantity expressing how much the measurements of time, length, and other physical properties change for an object while it moves.
The lorentz factor appears in special relativity questions.
Only velocities close to the speed of light (c) have an effect on time dilation or length contraction.
Velocities much less than c correspond to a lorentz factor of approximately 1.
What is the Doppler effect?
The change in frequency you notice when a source of sound waves move relative to you.
When the source moves towards you, more waves reach you per second and the frequency is increased (-).
When the source moves away from you, fewer waves reach you per second and the frequency is decreased (+).
What is Redshift?
Redshift (Doppler shift) is how much frequency of a light from a far away object has moved towards the red end of the spectrum (ROYGBIV).
It is a measure of how much apparent wavelength of the light has been increased.
If a galaxy is redshifted, they were moving away at speed.
What is Blueshift?
This is when the redshift equation gives you a negative answer. This means the object is moving closer to you and is said to be blue shifted.
It is a measure of how much the apparent wavelength has been decreased.
What is Hubble’s Law?
The bigger the shift, the faster the galaxy moves.
The relationship between distance and speed of a galaxy is known as Hubble’s law.
What is a light year?
One light year is the distance travelled by light in one year.
((3x10^8) x 365 x 24 x 60 x 60) = One light year
True or false: An object with more momentum requires a large amount of force to get it moving and a large amount of force to bring it to rest.
True - Large mass + large velocity = large momentum
What is the Law of conservation of momentum?
The total momentum before a collision or explosion is equal to the total momentum after a collision or explosion in the absence of net external forces.
What is momentum measured in?
kgms^-1
What formula is used for two masses that collide and move apart with different velocities?
mAuA + mBuB = mAuA + mBuB
What formula is used for two masses that collide and stick together?
mAuA + mBuB = (mA + mB) x vAB
What is an explosion and what are examples?
One body original at rest will explode into two parts which move in different directions. Therefore the momentum at the beginning is 0 so at the end must also be 0.
e.g. Cannon ball firing, gun shooting.
What formula is used for explosions ? (one body becoming two seperate bodies)
mABu = mAvA + mBvB
How is the concept of impulse useful in situations including safety features?
It is useful in situations when the force isn’t constant and acts for a short period of time e.g. a golf ball being hit by a golf club. During this contact, the unbalanced force varies with time.
Impulse can help with safety features. If the force is decreased, the time of contact is increased. This is why cars have a crumple zone and helmets have padding. Increasing the time of contact also decreases the average force applied (reducing the damage on the human body).
NOTE: change in momentum doesn’t change.
How can the concept of impulse be seen in relation to Sport balls?
This can be seen in bouncing balls: a hard ball only deforms a little bit whilst a soft ball deforms more and so the time of contact is longer.
How do you find impulse from a force/time graph?
Ft = AreaUnderGraph
True or false: In any collision involving impulse, the unbalanced force calculated is the average force and the minimum force experienced would be less than the calculated average value.
False: In any collision involving impulse, the unbalanced force calculated is the average force and the maximum force experienced would be greater than the calculated average value.
How is the universe believed to have started?
With a big bang. All matter began with the big bang. It was expanding extremely fast from the moment the universe was created. Because the universes mass was so close together, gravity began slowing the universe down. But in the background there has always been a repulsive force called Dark Energy.
Do scientists believe that the Universes expansion is speeding up or slowing down?
As the Universe is so full of mass, scientists thought that all the mass and subsequent gravity would start to slow the expansion of the universe down. They believed that exploding stars were key to finding out about the expansion of the universe (known as type 1a supernovae). You can tell how far away a start is by observing its brightness. Exploding stars always give off approximately the same brightness. The process of an exploding star can take a few weeks and are observed over this period.
After finding some exploding stars, scientists discovered that the exploding stars where actually dimmer than they should have been and had been moving away. They were so far away that the only explanation would be that they were accelerating away and not slowing down meaning the universe is expanding.
Scientists also calculated the mass of the universe to be a negative value which is impossible. They then realised that their calculations were based on the expansion of the universe slowing down. Re-doing the calculations, assuming the expansion to be speeding up, showed that the universe must be expanding.
How can we estimate the mass of the universe and in what relation does this have to Dark matter?
The mass of objects in space can be estimated due to their orbital speed. The masses measured seem to be bigger than the mass that can be accounted for by the number of stars present in our galaxy. Therefore it is theorised that there is something else making up this mass which we can’t see called Dark Mattee.
What did Dark Energy do?
As the distance between the universe’s mass became greater, the gravitational pull faded. As gravity weekend, the repulsive force took over and began forcing the universes expansion to speed up
What are the two possible outcomes for the universe in the future?
- Closed universe - the universe will begin to slow its expansion and eventually begin to contract.
- Open universe - the universe will continue to expand forever.
True or false: The further away the galaxy is, the higher the average velocity. This shows that the universe is accelerating. This can be represented on a Hubble’s Law graph.
True
True or false: The objects within the universe are expanding with the universe and the expansion of the universe is decelerating.
False: The objects within the universe aren’t expanding, whereas the distance between them is. The expansion of the universe is accelerating.
What is the estimated overall mass of the Milky Way?
760 billion to 1 trillion solar masses.
True or false: The orbital speed of the Sun and other stars gives a way of determining the mass of our galaxy.
True.
True or False: The faster the galaxy expands, the faster the acceleration of the objects within the galaxy.
True
What happens to the colour of objects as they are heated and what is an application of this?
When an object is heated, it radiates large amounts of infrared radiation.
As an object becomes hotter and begins to glow, it becomes a dull red, then a bright red, then orange, then yellow and finally white. At extremely high temperatures it becomes a bright blue - white colour.
Pottery - Potters used this fact to determine the temperature inside their kilns.
True or false: The temperature of an objects is linked to both frequency and wavelength of the light it emits.
True
Planck distribution graph description.
Intensity of wavelength x temperature.
As the temperature of the object increases, the peak intensity wavelength decreases so frequency increases.
As the temperature of the object increases, the intensity of the energy increases.
SUMMARY
As temperature goes up, wavelength goes down therefore frequency goes up and energy goes up.
What is the Big Bang theory?
It took place 13.8 billion years ago.
The universe was originally very hot and very dense concentrated in a tiny point known as a singularity. It caused our universe to expand suddenly bringing time and space into existence. Following the Big Bang, temperatures rapidly cooled and tiny particles of matter began to form. The first particles to form were hydrogen and helium. This matter created stars, galaxies and planets.
What three pieces of evidence are there to support the big bang?
- The expanding universe - Darkness of the sky. The only explanation is that the stars are moving away from us (redshifted)
- Cosmic Microwave Background Radiation - This radiation can be detected on Earth coming from all directions in space. This radiation is constant throughout the universe. As the universe expands the wavelength of the radiation emitted increases (less frequency) down to the microwave region. The radiation provided a constant temperature throughout the universe (3K). The radiation curve of microwaves match the black body radiation which is some of the main evidence of the big bang.
- Abundance of light elements - The universe has an abundance of light elements such as Hydrogen and Helium, as the universe grew these elements fused together to create other known elements.
How to measure the temperature of the universe?
We can find the average temperature of the universe which can provide evidence for the big bang. We can measure the temperature of a star by looking for a peak in the wavelengths emitted. High temperature = emit more radiation = shorter wavelengths.
What is a black hole?
They are formed when large dense stars collapse near the end of their life. The collapse creates a gravitational field which is so strong that all matter and light are attracted into the star. Nothing can escape a black hole.
UNIFORM AND RADIAL FIELDS
don’t need to know for assessment
What is dark energy?
Gravity is the force which slows down the expansion of the universe. But the rate of expansion appears to be increasing. This implies that there is an energy opposing gravity, called dark energy.
What is black body radiation?
Thermal radiation emitted by bodies.
The curve following a planck distribution graph.
Each curves correspond to a different black body temperature.
The expanding universe experiment
If another point orbits half way between the star and the orbiting point, how many times greater will the gravitational force between star A and the new point be?
4 times greater
What is ‘c’ always equal too?
The speed of light unless told otherwise.
True or false: If a graph has a systematic uncertainty, the line of best fit does not go through the origin.
True
If a weight reduces and the upward force remains constant, what will happen to the vertical motion of the object?
It would accelerate upwards as the upwards force is greater than the weight.
Why must a force be increased with time to remain constant acceleration?
Frictional force increased with speed so the force must be increased to ensure a constant unbalanced force.
