# OCR Physics A Newtonian World (G484) definitions

Learn and practice your knowledge of these definitions using Quizlet.

#### Units

radian – an alternative unit for measuring angles ( )
kelvin – unit of thermodynamic temperature (equal to degrees celsius + 273.15)

#### Quantities

linear momentum – the product of mass and velocity
net force on a body – rate of change of its momentum
impulse of a force – force multiplied by the time for which the force acts
centripetal force – the net force on acting on an object moving in a circle; it is always directed towards the centre of the circle
gravitational field strength – force per unit mass
period of an object describing a circle – the time taken by an object to complete one orbit
displacement – distance from an equilibrium position
amplitude – maximum displacement
period – the time taken for one complete oscillation of a vibrating object
frequency – number of oscillations per unit time
angular frequency phase difference – the fraction of an oscillation between the vibrations of two oscillating particles (expressed in degrees or radians)
pressure – force per unit area
internal energy – the sum of the random distribution of kinetic and potential energies associated with the molecules of a system
latent heat of fusion – the thermal energy required to turn a solid into a liquid at constant temperature
latent heat of vaporisation – the thermal energy required to turn a liquid into a gas at constant temperature

#### Concepts

Newton’s first law – a body will remain at rest or continue to move with constant velocity unless acted upon by a force
Newton’s second law – rate of change of momentum is equal to the net force acting and takes place in the direction of that force.
Newton’s third law – when one body exerts a force on another, the other body exerts an equal (in magnitude) and opposite (in direction) force on the first body
equilibrium – resultant force is zero
principle of conservation of momentum – total momentum is constant for a closed system
perfectly elastic collision – a collision with no loss of kinetic energy
inelastic collision – a collision with some loss of kinetic energy
Newton’s law of gravitation – force between two masses is proportional to the product of the masses and inversely proportional to the square of the distance between them
geostationary orbit – an equatorial orbit with a period of 24 hrs, moving from west to east
Kepler’s third law – the cube of a planet’s distance from the Sun is proportional to the square of its orbital period
simple harmonic motion – acceleration is directly proportional to displacement and is directed in the opposite direction to the displacement
thermal equilibrium – no net heat flow between objects
absolute zero – the temperature at which a substance has minimum internal energy
specific heat capacity – the energy required per unit mass of a substance to raise its temperature by 1K
Boyle’s law – pressure is inversely proportional to volume for a fixed mass of gas at a constant temperature

Basic assumptions of the kinetic theory of gases:

• particles move with rapid, random motion
• all collisions are elastic
• volume of atoms is negligible (compared with volume of container)
• no intermolecular forces (except during collisions)
• collision time is negligible (compared to time between collisions)

Useful applications of resonance:

• cooking: microwaves cause water molecules to resonate
• woodwind instrument: reed causes air column to resonate
• brass instrument: lips cause air column to resonate
• MRI: radio waves in a magnetic field cause protons to resonate