phys promos Flashcards
progressive wave
transports energy from one point to another in the direction of wave propagation
newtons 1st law
a body continues in its state of rest or uniform motion in a straight line unless a resultant external force acts on it (inertia)
newtons 3rd law
if body a exerts a force on body b, body b will exert an equal and opposite force on body a (action reaction pair, must be different bodies, do not cancel, same type)
mass
intrinsic property of a body which resists change in motion
weight
force experienced by a mass in a gravitational field
conditions for equilibrium
- resultant force on body is zero
- resultant torque on body about any axis is zero
momentum
product of mass and velocity
newtons 2nd law
rate of change of momentum is proportional to the resultant force acting on it and occurs in the direction of the force
impulse
product of force acting on object and time for which force acts
principle of conservation of momentum
when bodies in a system interact, the total momentum of the system remains constant, provided no net external force acts on it
completely inelastic collsion
bodies stick together after collision, final velocity same, total momentum conserved, total ke not conserved
principle of flotation
object floating in equilibrium, upthrust is equal in magnitude and opposite in direction to the weight of object/weight of fluid displaced
principle of moments
for body in rotational equilibrium, sum of clockwise moments about any axis is the same as the sum of anticlockwise moments about the same axis
couple
pair of equal and opposite forces whose line of action do not coincide
centre of gravity
point at which the whole weight of the body appears to act
angular displacement
angle the object makes with respect to a reference line
angular velocity
rate of change of angular displacement with respect to time
period
time taken for one complete oscillation
frequency
number of complete oscillations per unit time
object moving in uniform circular motion must experience a force
according to newtons first law, object will continue to move at its constant speed in the same direction unless there is a net force acting on it. hence must have a force acting on the object to constantly change its direction of motion
why acceleration directed towards centre
object is moving at constant speed, no component of force (acceleration) in the direction of motion of object, otherwise will increase or decrease the speed of the object. thus direction of force has to be perpendicular to direction of motion
simple harmonic motion
motion of a particle about a fixed point such that its acceleration is proportional to its displacement from the fixed point and is always directed towards the point
angular frequency
rate of change of phase angle of oscillation and us equal to the product of 2 pi and its frequency
damping
energy is removed from an oscillating system
resonance
system responds at maximum amplitude to an external driving force. occurs when frequency of the driving force is equal to the natural frequency of the driving system
transverse waves
particles oscillate in a direction perpendicular to the direction of energy transfer
longitudinal waves
particles oscillate in a direction parallel to the direction of energy transfer
polarisation
oscillations of the wave particles in transverse waves are restricted to one direction only and this direction is perpendicular to the direction of energy transfer
malus law
intensity of beam of plane polarised light after passing through a plane polariser varies with the square of the cosine of the angle through which the polariser is rotated that gives maximum intensity
principle of superposition
two or more waves of same kind meet at a point in space, resultant displacement at that point is equal to the vector sum of displacement of the individual waves at that point
stationary wave
result of the superposition of the 2 progressive waves of the same type, freq, amplitude and speed, travelling along the same line but in opposite directions
antinode and node
antinode point where amplitude is max
node point where amplitude is zero
diffraction
bending of waves after passing through an aperture or round an obstacle
coherent
constant phase difference and same frequency
interference
superposition of 2 or more waves to give a resultant wave whose resultant amplitude is given by the principle of superposition
constructive and destructive
2 coherent waves arrive at same point with phase difference of zero to produce a maximum
2 coherent waves arrive at the same point with phase difference of pi rad to produce a minimum
newtons law of gravitation
2 point masses attract each other with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them
gravitational field
region of space in which a mass placed in that region experiences a gravitational force
gravitational field strength
gravitational field strength at a point in space is the gravitational force experienced per unit mass at a point
gravitational potential energy
work done by external force in bringing a mass from infinity to that point
gravitational potential
work done per unit mass by an external force to bring a small test mass from infinity to that point
why gravitational potential negative
gravitational force is attractive in nature. to bring a small test mass from infinity to a point, work done by external force is opposite to the direction of displacement of the mass. negative work done by external force thus negative
escape velocity
minimum speed for the object to just escape from the gravitational influence of a massive body
