ODU Flashcards
State the definition of acceleration
acceleration is the rate of change of velocity
the gradient of an s-t graph gives…
velocity
the gradient of a v-t graph gives…
acceleration
the area under a v-t graph gives…
displacement
the area under an a-t graph gives…
velocity
how do you know that the vector on a motion-time graph has started acting in the opposite direction?
The graph crosses the time axis
explain satellite motion
the satellite is in freefall around a planet. It follows a circular path because it has a constant velocity at a tangent to the planet and a constant acceleration towards the planet. The projectile does not it the planet because it has velocity at a tangent to the planet’s surface.
Projectiles have constant horizontal ________ and constant vertical ________ in the absence of friction
Projectiles have constant horizontal velocity and constant vertical acceleration in the absence of friction
Always consider _______ and ________ components separately
Always consider horizontal and vertical (i.e. perpendicular) components separately
state newton’s first law
newton’s first law states that an object at rest will remain at rest and an object in motion will remain in motion with constant velocity unless acted upon by an unbalanced force
State a corollary of newton’s first law (just checking you know the implications of newton 1)
an object will accelerate when acted upon by an unbalanced force
state what is meant by the phrase “balanced forces”
forces have the same size but opposite direction (i.e. there is no net force on an object)
state newton’s second law
the vector sum of forces on an object is equal to the product of the mass and acceleration of an object i.e. ΣF = ma
State newton’s third law
Every action force has an equal and opposite reaction force. Remember: The action and reaction force act on different objects. Newton 3 applies to interaction between objects
state what is meant by “friction”
Friction is a force which opposes the motion of an object
state what is meant by “tension”
Tension is a force which is transmitted from one object to another via a coupling. It acts in opposite directions on each object
State what is meant by “terminal velocity”
terminal velocity is the maximum velocity of an object in freefall when friction is taken into account. It happens when weight = -friction
What does the reading on a scale calibrated in newtons tell you?
the normal reaction force
Explain why the reading on a scale changes when in a lift
w = mg acts downwards and doesn’t change. N is the normal reaction force. This changes depending on the acceleration of the lift: ΣF = ma => N-mg = ma. The scales show N.
State the equation for calculating the component of an object’s weight acting down a slope
mgsin(θ)
State the equation for calculating the component of an object’s weight perpendicular to a slope
mgcos(θ)
State the law of conservation of momentum
The total momentum before a collision/explosion is equal to the total momentum after a collision/explosion in the absence of external forces
State what is meant by the term “elastic collision”
Both kinetic energy and momentum are conserved
State what is meant by the term “inelastic collision”
Momentum is conserved but kinetic energy is not
How is impulse calculated from a force-time graph?
By finding the area under the graph
State two equations for impulse
Impulse = Ft and Impulse = mv - mu
Explain how the force of an impact can be reduced
By increasing the time of the collision i.e. increasing t in F = (mv - mu)/t. t goes up, F goes down
When calculating the force of gravitational attraction between two masses, between where is their separation measured?
The centres of the masses
State Einstein’s postulates
- The laws of physics are the same in all inertial reference frames. 2. The speed of light is constant in all inertial reference frames and independent of the motion of its source
State what is meant by the term “time dilation”
Time dilation is the increase in time for an event occurring in a moving frame as measured by a stationary observer. t’ = dilated time
Identify the symbols t, t’, l and l’
t=proper time, t’=dilated time, l=proper length, l’=contracted length
Describe the Doppler Effect
The frequency of sound emitted by a moving source is observed to increase when it approaches an observer and fall as it moves away
Explain the Doppler Effect
Frequency increases on approach because the source catches up with the sound it is emitting, meaning that the wave peaks are closer together and the frequency increases. Frequency decreases as the source moves away because the source moves away from the sound it emits, stretching the wave peaks apart and decreasing its frequency.
In the equation for Doppler Effect, do you use a + sign when the source is coming towards you or moving away from you?
Moving away. Putting a + sign makes the denominator bigger and therefore the observed frequency smaller, which happens when the source moves away from the observer.
When a source of sound waves is moving towards you, do you observe a higher or lower frequency?
Higher because the waves become bunched up and the frequency increases
State 4 pieces of evidence to support the Big Bang theory and universal expansion.
CMBR, the relative abundances of hydrogen and helium, the darkness of the night sky, the large number of galaxies showing redshift rather than blueshift
How can the mass of a galaxy be estimated?
By measuring the orbital velocity of stars and using newton’s law of gravitation
Why does the high orbital velocity of stars near the edges of galaxies provide evidence for the existence of dark matter?
The orbital velocities of stars within a galaxy does not reduce as one might expect, rather it increases the eventually levels off. This suggests that there is matter which we cannot see located at the outer edges of a galaxy
State one piece of evidence for the existence of dark matter
The orbital velocities of stars within a galaxy is larger than expected due to all visible matter. This leads us to calculate the masses of galaxies which are much larger than can be accounted for by visible matter and suggests the existence an some unseen, dark matter.
State one piece of evidence for the existence of dark energy
The accelerating rate of expansion of the universe
As the temperature of a star increases, what happens to the peak wavelength at which it emits light?
It gets shorter
Which object will emit more radiation per unit surface area per unit time: a hot one or a cold one?
A hot one
How does the distribution of radiation emitted by a star change as its temperature increases?
Hotter objects emit more radiation at all wavelengths than colder ones and the peak wavelength at which they emit radiation decreases
What is an order of magnitude?
It is a power of 10
State what is meant by the term “fermion”
A fermion is a matter particle
State what is meant by the term “boson”
A boson is a force mediating particle
Quarks are ______
fermions (i.e. matter particles)
Leptons are ________
fermions (i.e. matter particles)
List the 6 quarks
Up down strange charm top bottom
List the 6 leptons
electron, muon, tau, electron neutrino, muon neutrino, tau neutrino
List the 4 force mediating particles and their associated force
Photon (electromagnetic force), Z & W+- bosons (weak force), gluon (strong force)
Which force is missing from the Standard Model
Gravity
What is the standard model?
A model of fundamental particles and their interactions
What are hadrons made up of?
Hadrons are composite particles made of quarks
Baryons are a type of ________ and they are therefore made-up of ________
hadron, quarks
Mesons are a type of ________ and they are therefore made-up of ________
hadron, quarks
Baryons are made of _______ quarks
3
Mesons are made of…
a quark-antiquark pair
Describe beta decay and how it is evidence for the existence of the neutrino
beta decay is when a neutron turns into a proton, electron and an anti electron neutrino. The mass after beta decay was much smaller than could be accounted for by mass-energy conversion and pointed to the existence of a new particle, the neutrino
State what is meant by “anti-matter”
Every particle in the standard model has a corresponding anti-particle, identical in every way except charge. These particles are called “anti-matter”.
State one piece of evidence for the existence of antimatter.
When matter meets antimatter they annihilate
