Our Dynamic Universe - Definitions Flashcards
Speed
The distance travelled per unit time
Velocity
The displacement per unit time
acceleration
- The change in velocity per unit time
- Given by the gradient on a velocity time graph
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.
Terminal Velocity
For an object in free-fall, a constant speed is reached when the upward force on the object (air resistance) is balanced by the downward force on the object (weight)
Newton’s 3rd Law
For every action there is an equal but opposite reaction
Principle of Conservation of Energy
Energy cannot be created or destroyed, but can change from one form to another
Inelastic Collision
- A collision in which momentum is conserved but kinetic energy is not
- Some of the kinetic energy is converted to heat and sound upon impact
Elastic Collision
A collision in which both momentum and kinetic energy are conserved
Impulse
- The product of force and time
- It is a vector quantity
Projectile motion
The curved path taken by a projectile due to it’s constant horizontal velocity and constant vertical acceleration
Satellite
A special type of projectile that follows a circular orbit due to it’s constant horizontal velocity and constant vertical acceleration
Free-Fall
The movement of any object under the influence of gravity alone
Einsteins Postulates
- the laws of physics are the same for all freely moving observers
- the speed of light in a vacuum is the same for all observers regardless of their velocity
Time Dilation
the apparent increase in time of an event for an object moving relative to an observer
length contraction
the apparent decrease in length of an object moving relative to an observer
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 of galaxies that are moving away from us is shifted into longer (i.e Redder) wavelengths
- Redshift is the ratio of the velocity of the galaxy to the velocity of light
Hubble’s Law
the recessional velocities of distant galaxies are directly proportional to their distance from us
Dark Matter
accounts for the observation of unusually high orbital speeds of stars on the outer arms of galaxies
Dark energy
accounts for the observation that the expansion of the universe is accelerating.
resultant of a number of forces
A single force which has the same effect as all other forces combined together as vectors
