All OCR A A-Level Physics Definitions Paper 1

What are the SI base units?

Metre, kilogram, ampere, mole, second, kelvin

Scalar quantity

Has magnitude but no direction

Vector quantity

Has both magnitude and direction

Acceleration

rate of change of velocity

Define the Newton

the force that causes a mass of 1kg to have an acceleration of 1ms^-2 in the direction of the force

Tension

The force within a stretched cable or rope

Normal contact force

The force that arises when one object rests against another

Upthrust

An upward buoyancy force acting on an object when it is in a fluid

Friction

A force that opposes motion between two surfaces that are in contact

Drag

The frictional force experienced by an object travelling through a fluid

moment

Force x perpendicular distance from point of rotation

Principle of moments

For a body in rotational equilibrium, the sum of the anticlockwise moments about a point is equal to the sum of the clockwise moments about the same point

Centre of gravity

The point where the entire weight of an object appears to act.

Centre of mass

A point through which any externally applied force produces straight-line motion but no rotation

Torque

one of the forces x perpendicular separation between the forces

Density

Mass per unit volume

Pressure

Force per unit area.

Pressure in a fluid at any depth...

same in all directions

Archimede's Principle

The upthrust exerted n a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces

Joule

1 Nm

Energy

the capacity to do work

Principle of conservation of energy

The total energy of a closed system remains constant; energy can not be created or destroyed, only transferred from one form to another

Power

the rate at which work is done

Watt

One joule per second

Hooke's Law

The extension of a spring is directly proportional to the force applied, as long as the elastic limit is not exceeded

Tensile stress

Force per unit cross-sectional area

Tensile strain

The fractional change in the original length of the wire

Ultimate tensile strength

The maximum stress that a material can withstand before it breaks

Young Modulus

The ratio of stress to strain for a particular material

Newton's First Law

An object will remain at rest or continue to move at a constant velocity, unless acted upon by a resultant force

Newton's Third Law

When two objects interact they exert equal and opposite forces on each other (of the same type, and never on same object)

Conservation of momentum

For a system of interacting objects, the total momentum in a specified direction remains constant, as long as no external forces act on the system

Perfectly elastic collision

A collision where total kinetic energy is conserved

Inelastic collision

Collision where total kinetic energy is not conserved

Newton's Second Law

The net force acting on an object is directly proportional to the rate of change of its momentum, and is in the same direction

Impulse of a force

change in momentum

Thermal equilibrium

Net flow of thermal energy between objects is zero

Kinetic model of solids

Atoms or molecules regularly arranged and packed closely together, with strong forces of electrostatic attraction between them holding the m in fixed positions, but they can vibrate so have kinetic energy

Kinetic model of liquids

Atoms or molecules still close together, but have more kinetic energy than solids, they can change position and flow past each other

Kinetic model of gases

Atoms or molecules have more kinetic energy than liquids, and are much further apart. Free to move past each other as negligible electrostatic forces of attraction between them unless they collide with each other or container walls. Move randomly with different speeds in different directions.

Brownian motion observations

Particles move randomly, smoke particles much larger than air molecules

Inernal Energy of a Substance

The sum of the randomly distributed kinetic and potential energies of atoms or molecules within a substance

Electrostatic potential energy...

Zero in gases, more negative in liquids, most negative in solids

Why are electrostatic potential energies negative?

Energy must be supplied to break atomic or molecular bonds

At absolute zero....

Internal energy is minimum

Specific heat capacity

The energy per unit mass required to change the temperature by 1K

Specific latent heat

Energy supplied to change the phase of a mass of a substance

Specific latent heat of fusion

the energy needed to change a unit mass from the solid to the liquid phase at constant temperature

Specific latent heat of vaporisation

the energy needed to change a unit mass from the liquid to the gas phase at constant temperature

One mole

The amount of substance that contains as many elementary entities as there are atoms in 12g of Carbon-12

Kinetic theory of gases assumptions

Very large number of atoms or molecules moving in random directions with random speeds, occupy a negligible volume compared with the volume of the gas, collins with each other and the container walls are perfectly elastic, time of collisions between atoms with each other or container walls is negligible compared to the time between the collisions, electrostatic forces negligible except during collisions

Boyle's Law

If the temperature and mass of a gas is constant, its pressure is inversely proportional to its volume

Relationship between pressure and temperature of an ideal gas

If the volume and mass of a gas is constant, its pressure is directly proportional to its temperature

Internal energy of an ideal gas

Entirely in the form of kinetic energy and electrostatic forces between atoms or molecules are negligible

The radian

The angle subtended by a circular arc with length equal to the radius of the circle

Degrees to radians conversion

Divide angle in degrees by π/180

Angular velocity

rate of change of angular displacement

For body to move in a circular path with a constant velocity

Resultant force must be perpendicular to the velocity so no force in direction of motion; no work done on object

OM; displacement

Distance from the equilibrium position

OM; amplitude

Maximum displacement from the equilibrium position

Om; period

The time taken for one complete oscillation

OM; frequency

The number of oscillations per unit time

Simple harmonic motion

Oscillating motion where acceleration is directly proportional to displacement and directed towards a fixed point

Isochronous oscillator

An oscillator that has the same period regardless of amplitude

Free oscillation

When a mechanical system is displaced from its equilibrium position and allowed to oscillate without any external forces

Forced oscillation

An oscillation in which a periodic driver force is applied to an oscillator

Frequency of free oscillation

Natural frequency

Frequency of forced oscillation

Driving frequency

Resonance

When the driving frequency is equal to the natural frequency, amplitude of oscillation increases significantly and if not damped system may break

Gravitational field strength

Force exerted per unit mass

Newton's Law of Gravitation

The force between two point masses is directly proportional to the product of the two masses and inversely proportional to the square of the separation

Kepler's First Law

The orbit of a planet is an ellipse, with the sun at of of the two foci

Kepler's Second Law

A line segment joining a planet and the sun sweeps out equal areas in equal intervals of time

Kepler's Third Law

The square of the orbital period of a planet is directly proportional to the cube of its average distance from the sun

Uses of satellites

Communications, GPS, weather monitoring

Geostationary satellites

Equatorial orbit, rotate in sae direction as earth's rotation, have an orbital period of 24 hours

Gravitational potential

Work done per unit mass in bringing an object from infinity to a point

Escape velocity

the minimum velocity needed to escape a gravitational field

Planet

An object in orbit around a star that has a mass large enough for its own gravity to give it a round shape, has no fusion reactions, and has cleared its orbit of most other objects

Planetary satellites

A body in orbit around a planet

Comet

Small, irregular bodies made up of ice and dust and small pieces of rock, in orbit around the sun

Solar system

The sun and all the objects that orbit it

Galaxy

A collection of stars, and interstellar dust and gas

Electron degeneracy pressure

When core of a star begins to collapse under the fore of gravity, electrons are squeezed together which creates pressure that prevents core from further gravitational collapse

Chandrasekhar limit

electron degeneracy pressure is only sufficient to prevent gravitational collapse if the core has a mass less than 1.44 solar masses

Neutron star

Very small, very dense star that remains after a supernova

Black hole

Very dense, gravitational field so strong light cannot escape it

Emission line spectra

Each element produces a unique emission line spectrum because of its unique set of energy levels

Continuous spectra

All visible frequencies or wavelengths are present.

Absorption line spectra

dark spectral lines against a continuous spectrum

Wien's displacement law

Maximum wavelength is inversely proportional to temperature

Stefan's law

The total power radiated per unit surface area of a black body is directly proportional to the fourth power of the absolute temperature of the black body

Astronomical unit

The average distance from the earth to the sun

Light year

The distance travelled by light tin a vacuum in the time of one year

Parsec

The distance at which a radius of 1 AU subtends an angle of 1 arc second

Stellar parallax

The apparent shift in the position of a nearby star against a backdrop of much more distant stars as the earth orbits the sun

The doppler effect

Whenever a wave source moves relative to an observer, the frequency and wavelength of the waves received by the observer change, compared to what would be observed without relative motion

Hubble's Law

The recessional speed of a galaxy is almost directly proportional to its distance from the earth

Hubble's observations

Light from the majority of galaxies is red shifted, so relative velocity away from earth and the further away the galaxy the greater the red shift, so the faster the galaxy was moving

Cosmological principle

When viewed on a large enough scale, the universe is homogenous and isotropic, and the laws of physics are universal