Our Dynamic Universe Key Terms Flashcards
Scalar
A quantity fully described by it’s magnitude.
Vector
A quantity fully described by magnitude and direction.
Distance
How far an object has travelled from starting point to finishing point of a journey. It is a scalar quantity.
Displacement
- How far you are from your starting point.
- vector quantity
- given by area under velocity-time graph
Speed
The distance travelled per unit time. (scalar quantity)
Average speed
The total distance travelled by an object measured over the total time taken.
Velocity
The displacement per unit time. (vector quantity)
Acceleration
- The change in velocity per unit time
- vector quantity
- gradient of v-t graph
Friction
A force which opposes the motion of an object.
Balanced forces
when the forces acting on an object are equal in magnitude but opposite in direction.
Unbalanced forces
when the forces acting on an object are different in magnitude and different in direction.
Newton’s 1st Law
An object will remain at rest or move at a constant speed in a straight line unless acted on by an unbalanced force.
Newton’s 2nd Law
When the forces acting on an object are unbalanced, the object will accelerate in the direction of the unbalanced force.
Newton’s 3rd Law
Every action has an equal and opposite reaction.
Newton pairs
action and reaction forces for a specific situation involving Newton’s 3rd Law.
Tension
the pulling force of a string, cable or chain.
Free-fall
describes the movement of any object under the influence of gravity alone.
Terminal velocity
a constant speed reached when the upward force on the object (air resistance) is balanced by the downward force on the object (weight).
Weight
- the force due to gravity acting on an object
- vector
- measured in newtons
Work done
- a form of energy measured in joules
- describes the force applied to move an object a certain distance.
Gravitational potential energy
the energy stored by an object as a result of its vertical position above the surface of the Earth.
Kinetic energy
the energy possessed by a moving object
Law of Conservation of energy
Energy cannot be created or destroyed, but can change from one form to another.
Power
the rate at which energy is converted into other forms.
Momentum
-the product of mass and velocity.
Principle of Conservation of Momentum
The total momentum before a collision is equal to the total momentum after a collision in the absence of external forces.
Inelastic collision
a collision in which momentum is conserved but kinetic energy is not. (some kinetic energy is converted to heat and sound upon impact)
Elastic collision
a collision in which both momentum and kinetic energy are conserved.
Explosion
- an object ‘explodes’ into two parts which move off in opposite directions.
- total momentum is conserved and will be zero before the explosion.
Impulse
- the change in momentum of an object
- given by the area under a force-time graph.
Airbags
- safety feature in vehicles.
- increase time taken for a person’s head to decelerate to rest which therefore reduces the average force exerted on the person’s head.
Crumple Zones
- safety feature at front and rear of vehicles
- increase time taken for vehicle to decelerate to rest on impact and therefore reduce the average force exerted on passengers.
Projectile
any object that is launched and moves under the influence of gravity.
Trajectory
the path taken by a projectile
Range
the horizontal distance travelled by a projectile
Projectile motion
the curved path taken by a projectile due to its constant horizontal velocity and constant vertical acceleration.
Time of flight
- the time that a projectile travels for
- horizontal time is equal to vertical time.
Satellite
- a projectile that follows a circular orbit due to its constant horizontal velocity and constant vertical acceleration.
- accelerates towards the surface of the Earth due to its weight.
Satellite orbit
the path followed by a satellite
Gravitational field
the gravitational force per unit mass
Newton’s Law of Universal Gravitation
- every object in the universe with a mass attracts every other object with a mass.
- the gravitational force of attraction between two objects depends on the Universal Constant of Gravitation, the mass of each object and the distance between the two objects.
Frame of Reference
A point of view from which an observer can measure physical quantities. Also known as a reference frame.
Inertial Frame of Reference
A non-accelerating frame of reference in which Newton’s 1st law holds.
Special Relativity
Deals with the special case of inertial frames of reference in which objects are
either at rest or moving at constant speed relative to one another
Einstein’s Postulates
- The laws of physics are the same for two observers moving at constant
speed relative to one another. - The speed of light in a vacuum is the same for all observers.
Time Dilation
The apparent increase in time of an event for an object that is moving relative
to an observer
Length Contraction
The apparent decrease in length of an object that is moving relative to an
observer
Lorentz Factor
For non-relativistic speeds, the Lorentz factor, γ, becomes approximately equal
to 1. This means that relativistic effects are negligible (can be ignored).
Doppler Effect
The change in frequency observed when a source of sound (or light) waves
moves relative to an observer.
Redshift
When light from stars or galaxies that are moving away from us is shifted to
longer (more red) wavelengths. It is an example of the Doppler Effect
Blueshift
When light from stars or galaxies moving towards us is shifted to shorter (more
blue) wavelengths.
Hubble’s Law
-The recessional velocity of distant galaxies is directly proportional to their
distance from us.
-The gradient of the line of best fit on a graph of recessional velocity of galaxies
(y-axis) against their distance (x-axis) gives Hubble’s constant, H0.
-It provides evidence for the Big Bang.
Age of the Universe
- Thought to be around 13.8 billion years (13.8 x 109
years) . - This can be proved using Hubble’s law and the speed-distance-time equation.
Dark Matter
-A considerable amount of matter in galaxies that we cannot see.
-It accounts for the observation of unusually high orbital speeds of stars on the
outer arms of galaxies.
-It is thought to make up around 22% of all matter in the Universe.
Dark Energy
-A source of energy capable of producing a force which acts against the
gravitational force of attraction, pushing matter apart.
-It accounts for the observation that the expansion of the Universe is
accelerating.
-It is thought to make up around 74% of all matter in the Universe
The Big Bang
-An effort to explain the origin of the Universe.
-It suggests that there was a rapid expansion of space from a singularity.
-The Universe was thought to start off extremely small and hot, which has since
expanded and cooled to this day.
Cosmic Microwave Background Radiation (CMBR)
-Evidence for the Big Bang.
-CMBR is background radiation coming from all directions in space.
-It is thought that this is radiation left over from an early stage in the
development of the Universe that has increased in wavelength (towards the
microwave part of the EM spectrum) due to the expansion of the Universe.
Olbers’ Paradox
-Evidence for the Big Bang.
-If the universe was infinitely old and contained an infinite number of stars, then
the night sky should be white due to stars being visible in any line of sight.
-Since the Big Bang theory supports the idea of an expanding Universe, only
light from stars within the observable Universe will reach us.
-The Big Bang theory gives a finite age to the Universe and explains the darkness
of the night sky.
