Forces, Space and Radioactivity

GCSE Physics Flashcards

Braking Distance

The distance a car travels after the brakes have been applied.

Thinking Distance

The distance a car travels when the driver is reacting.

Factors affecting braking distance

Worn brakes/tyres; Icy/wet roads.

Factors affecting thinking distance

Alcohol; Drugs; Tiredness.

Inertia

A resistance to a change in motion.

Weight

The force of gravity acting on an object.

Mass

The amount of matter in an object.

Newton’s 3rd law

If a body A exerts a force on body B then body B exerts an equal and opposite force on body A.

Energy efficiency improvements in vehicles

Aerodynamic losses are reduced by more streamlined designs. Rolling resistance is reduced by having correctly inflated tyres. Stop – start systems reduce idling losses. Inertial losses are reduced by having lighter cars.

Common car safety features

Seat belts; Airbags; Crumple Zone.

Work done

A measure of the energy transfer.

Kinetic energy

A body’s energy by virtue of its motion.

Gravitational potential energy

A body’s energy by virtue of its position.

Law of Conservation of momentum

The momentum before (an interaction) = momentum after (interaction) provided no external forces act.

Principle of moments

For a body in equilibrium the sum of the clockwise moments = the sum of the anticlockwise moments about the same point.

Asteroid belt

The asteroid belt is located between Mars and Jupiter and contains many rocky asteroids and dwarf planets.

Comet's orbit

Comets have highly elliptical orbits, passing far out of our solar system.

AU and lightyear

1 A.U. is the mean distance from the Sun to the Earth. A light year is the distance that light will travel in 1 year.

Star balance in main sequence

Gravitational inward forces match the outwards combination of gas and radiation pressure forces.

Cosmological red shift

Wavelengths of the absorption lines are increased and this effect increases with distance. The light from further galaxies shows the most red shift due to it having travelled for a greater amount of time through an expanding universe. Therefore increasing the wavelength.

CMBR

At the time of the Big Bang high energy short wavelength gamma rays were produced. Over time as space expanded, these gamma rays also stretched forming microwaves. The CMBR fills all of space with (nearly) uniform intensity in all directions.

Isotope

Isotopes of the same element have equal numbers of protons but differing numbers of neutrons in their nuclei.

Unstable nuclei

An imbalance between the numbers of protons and neutrons in the nucleus (which causes radioactive emissions).

Man-made sources of background radiation

Medical uses; Nuclear weapons; Nuclear Power stations.

Natural sources of background radiation

Radon gas; Cosmic rays; Food and drink; Rocks and buildings.

Half-life

It is the time taken to halve the number of radioactive atoms / nuclei.

Nuclear Fission

Slow moving neutrons are absorbed by heavy U-235 nuclei during collisions releasing further fast moving neutrons (leading to a sustainable chain reaction).

Nuclear Fusion

Two light nuclei, such as heavy hydrogen, collide and fuse producing helium and releasing energy.