AQA Physics Unit 4

Pregunta	Respuesta
angle in radians	angle in degrees X (Pi/180)
angular speed	1. the rate of change of angular displacement 2. the angle an object rotates through per second
frequency	the number of revolutions/ oscillations per second (=1/T)
Time period	The time taken for one complete revolution/ oscillation
circular motion	Objects travelling in a circle in constantly changing direction, so it is accelerating. Due to Newton's 1st Law, this means a force is acting on the object, which is directed towards the centre of the circle
simple harmonic motion	The acceleration of an oscillating object is directly proportional to its displacement. AND It's acceleration is always directed towards the equilibrium (opposite to displacement)
Graphs for simple harmonic motion	Image: f5547108-86bb-4ba9-af11-5a28f01dff2c.gif (image/gif)
Cycle of oscillation	From maximum positive displacement to maximum negative displacement and back again.
Energy changes in an oscillating system	At maximum displacement, KE is 0, with all energy as PE. As object moves towards equilibrium, restoring force does work on object, transferring PE to KE. At equilibrium, KE is maximum while PE is 0. As object moves away, KE is transferred back to PE.
Simple pendulum time period	Time period is only affected by the length of the rope. Mass of bob and amplitude have no effect on T.
Free vibrations	When an object oscillates at its natural frequency (theoretically without any loss of amplitude).
Forced vibrations	An oscillating system is subjected to a periodic force.
Resonance	When the forced vibration matches the natural frequency (with a phase difference of Pi/2), causing maximum amplitude.
Damping	When an oscillating system loses energy (and therefore a decrease of amplitude) due to resistive forces.
Light damping	When a system oscillates with a gradual loss of amplitude each period.
heavy damping	When an system oscillates with a large loss of amplitude each over each period.
Critical damping	When an object reaches equilibrium (without oscillating) in the shortest time possible.
Overdamping	Object reaches equilibrium without oscillating slowly
Gravitational force field	A region in which an object experiences a non-contact force due to the presence of gravity
Radial field lines	Lines meet at the centre. As an object moves further away, the radial field lines become further apart, and so the force decreases
Newton's law of gravitation	For two objects displaced a distance apart, the gravitational force of attraction between the two objects is proportional to the product of the masses, and inversely proportional to the square of the distance between them.
Gravitational field strength (g)	The force per unit mass. (NKg^-1)
Gravitational potential (V)	The work done per unit mass to move an object from infinity to that point within the field. (Jkg^-1)
Why is it often negative?	Gravitational potential is negative at the surface of the mass, as work needs to be done against gravity to reach infinity (where it = 0)
Equipotentials	Lines/ surfaces that join together all the points that have the same gravitational potential
Orbital time period	T=(4Pi^2 X r^3/GM)^(1/2)
escape velocity	The minimum velocity needed by an object to escape the Earth's gravitational field, without falling back towards it due to the gravitational attraction. V=((2GM)/r)^(1/2)
Geostationary orbits	Travel at the same angular speed as the Earth turns on its axis (24hrs). This means that they are always in the same fixed position in the sky.
Charges	opposite charges attract. Force is - alike charges repel. Force is +
Electric field strength (E)	Force per unit charge on a small positive test charge placed at that point within the field (NC^-1)
Electric field lines	For positive point charges, field lines point away. On negative charges, the field lines point towards the point charge. For parallel plates, field lines move from the more positive plate to the plate with less positive charge.
Charged particles in uniform electric fields	A charged particle that enters an electric field will feel a constant force. positive charges: force acts in same direction as field lines. negative charges: force acts in the opposite direction.
Electric potential (V)	The work done per unit positive charge to move a small positive test charge from infinity to that point in the field. (V)
Main difference between electric and gravitational fields	Gravitational fields are purely attractive, while electric fields can be attractive or repulsive.

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	Creado por Will Welford hace casi 9 años