Science Topic Test March 25

Gravity

Gravity is a force that attracts all masses.

Mass

The amount of matter in an object (measured in kg).

Weight

The force of gravity acting on an object (measured in Newtons, N).

Weight Formula

Weight = Mass × Gravitational field strength (W = mg).

Gravitational field strength on Earth

On Earth, g ≈ 10 N/kg.

Gravitational field strength on Mars

On Mars, g ≈ 3.7 N/kg.

The Sun

The Sun is at the center of our Solar System.

Planet

Orbits a star (e.g., Earth).

Star

Produces its own light (e.g., Sun).

Galaxy

A huge collection of billions of stars (e.g., Milky Way).

Proxima Centauri

The closest star after the Sun, about 4 light years away.

Light year

The distance light travels in one year (~9.5 trillion km).

Day

The side of Earth facing the Sun.

Night

The side of Earth facing away from the Sun.

Earth's rotation

The Earth completes one full rotation in 24 hours.

Seasons

Caused by Earth's tilt as it orbits the Sun.

Summer (UK)

The Northern Hemisphere is tilted towards the Sun, resulting in longer days and more sunlight.

Winter (UK)

The Northern Hemisphere is tilted away from the Sun, resulting in shorter days and less sunlight.

Earth's orbit

Earth orbits the Sun once every 365¼ days (1 year).

Water Waves

Waves transfer energy from one place to another.

Transverse Waves

The movement of the wave is up and down, but the energy moves forward (sideways).

Crest

The highest point of a wave.

Trough

The lowest point of a wave.

Displacement

How far a point is from the middle line.

Amplitude

The maximum distance from the middle to a crest or trough. A higher amplitude means a stronger wave.

Reflection of Water Waves

When a wave hits a surface, it bounces back.

Superposition

When two waves meet, they combine for a short time.

Light Waves

Light is a transverse wave (like water waves).

Speed of Light

The speed of light in a vacuum: 3.0 × 10^8 m/s.

Reflection of Light

Reflection happens when light hits a surface and bounces back.

Law of Reflection

Angle of incidence = Angle of reflection.

Specular Reflection

Happens on smooth, shiny surfaces (e.g. mirrors, calm water). Produces a clear image.

Diffuse Reflection

Happens on rough, dull surfaces (e.g. paper, walls). Light scatters in different directions, so no clear reflection.

Refraction

Refraction happens when light changes speed when moving between different materials.

Bending of Light

Light bends when moving from air to glass (more dense material) or from glass to air (less dense material).

Pinhole Camera

A pinhole camera shows an upside-down image because light travels in straight lines and crosses over inside the camera.

Lenses

Lenses bend (refract) light to help focus images.

Convex Lens

Brings light rays together (converges them) to a focus.

Cornea

Transparent, curved surface that does most of the focusing in the human eye.

Retina

Detects light and sends signals to the brain.

Dispersion of Light

White light is a mixture of colours that splits into a spectrum of colours when passing through a prism or raindrop.

Spectrum of Colours

Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV).

Coloured Objects

A red apple absorbs all colours except red, which it reflects.

Coloured Filters

A red filter only lets red light through and absorbs all other colours.

Sound

A type of wave caused by vibrations.

Longitudinal Waves

Waves with vibrations parallel to wave direction.

Medium

Substance needed for sound to travel.

Compressions

Areas where particles are close together.

Rarefactions

Areas where particles are spread out.

Echo

Sound reflection off a surface returning to source.

Absorption

Process where materials take in sound energy.

Speed of Sound

Varies by medium; fastest in solids.

Frequency

Number of sound waves per second, measured in Hertz.

Pitch

Perceived frequency; higher frequency equals higher pitch.

Vibrating Objects

Sources of sound that create pressure waves.

Sound in Space

Cannot travel in a vacuum due to lack of particles.

Sound Reflection

Bouncing of sound waves off surfaces.

Soft Materials

Absorb sound, reducing noise levels in rooms.

Speed Comparison

Sound travels slower than light, e.g., thunder and lightning.

Slinky Spring

Demonstrates longitudinal wave motion through coil vibrations.

Sound Waves

Travel through air, water, or solids as longitudinal waves.