**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
- radios: radio waves cause electrons to resonate
- person on a swing: intermittent pushes cause swing to resonate

**Problematic examples of resonance:**

- bridges: wind causes bridge to resonate
- vehicles: engine vibrations cause panels/mirrors to resonate
- earthquakes: ground vibrations cause buildings to resonate