Main definitions Flashcards
a Torque
when a force causes a rotation around an axis
Moment of inertia
the measure of an object’s resistance to angular acceleration around a given axis
moment of inertia equations
point mass-hoop or hollow cylinder
rod about centre-horizontal rod with vertical axis down its middle
rod about end-end of horizontal rod touching vertical axis at right angle
disc about centre-hollow cylinder or disc
sphere about centre-sphere
The principle of conservation of angular momentum
In the absence of external torques, total angular momentum before equals the total angular momentum after
I1wo1+I2wo2=I1w1+I2w2
Gravitational field strength
defined as the gravitational force acting on a unit mass by a gravitational field
Conservative field
A field in which the work done (energy required) to move mass between two points in the field is independent of the path taken
e.g. gravitational field
gravitational potential (at a point in a field)
The work done (energy) in moving 1kg of mass from infinity to that point in the field.
Escape velocity
the minimum velocity needed for a mads to escape the gravitational field of an object completely (ie to reach infinity)
The equivalence principle
It is not possible to distinguish between the effects on an observer of a uniform gravitational field and of a constant acceleration
A geodesic
the shortest distance between two points
Freely moving objects and light (due to gravitational lensing) will follow geodesics in spacetime
Schwarzschild radius
radius/distance from the singularity (up to the event horizon) where spacetime is so distorted that not even light can escape it
(its escape velocity exceeds the speed of light)
Distance from the centre of a black hole to the event horizon
What interpretation does general relativity lead to?
that mass curves spacetime and that gravity arises from the curvature of spacetime
Luminosity of a star
the energy per second (power) a star radiated across all wavelengths into space
Apparent brightness
the luminosity falling on 1m^2 at a distance d from the star
Quantum physics
‘phenomena on the atomic scale which are observed to be quantised - i.e. only exist in well defined states rather than a continuous range’
Heisenberg’s uncertainty principle
It is not possible to know the position and momentum of a quantum particle simultaneously
It is not possible to know the lifetime and the associated energy change of a quantum particle simultaneously
Quantum tunneling
Potential wells form energy barriers which would not normally allow particles to escape.
The quantum particle can ‘borrow’ energy for a short period of time and occupy states that, according to classical physics, it has insufficient energy to occupy
Explanation if helical motion
Charged particles entering a magnetic field at an angle will travel in a helical path due to the combination of its circular motion perpendicular to the field and its linear motion parallel tot he field
simple harmonic motion
The restoring force (and acceleration) is directly proportional to, and in the opposite direction to, the displacement from the rest position
What does damping refer to?
The energy lost from an oscillating system over time. The result is that amplitude of the oscillation decays over time (underdamping
overdamping and critical damping
-the object is brought slowly back to equilibrium with no oscillations
-the oscillator comes to a stop in the minimum possible time e.g. car shock absorbers
wave
A disturbance in a medium which transfers energy from one place to another
Amplitude
A measure of the energy transferred by a wave- as amplitude increases, so does energy transferred
What is the phase difference between 2 points on a wave a distance x apart?
Their separation as a fraction of the wavelength, expressed as a phase angle in radians
When is a stationary wave formed?
When the incident wave and the reflected wave interfere to produce points if destructive and constructive interference
The waves reflected from each end interfere to produce maxima and minima
By the interference between 2 waves of the same frequency and amplitude, travelling in different directions
Transverse waves
oscillations of the wave medium are at right angles to the direction if travel
unpolarised transverse waves
They can have oscillations in any random direction, just as long as they are at right angles to the direction of travel
Plane polarised light
The oscillations of the wave are restricted to 1 plane
It has oscillations of the electric field vector restricted to a single plane
non-inertial frames of reference
frames of reference that are accelerating with respect to an inertial frame
