sci sw 1 sem 2

• to vibrate means to move backwards and forwards very quickly
• sound travels from a vibrating object to our ears is called sound wave
• everytime an object vibrates forwards, the air in front of the object gets pushed forwards
• the particles in the air are made to vibrate backwards and forwards in time with the vibrating object
• the speed of sound waves in air is about 343 metres per sound
• sound waves transfer sound energy
• sound waves travel by making particles vibrate
• sounds also travel through liquid
• the substance that the sound wave moves through is called medium
• sound waves can be reflected from surfaces
• the reflection of a sound wave is called an echo
• an opaque object is an object that will not allow light to pass through
• when an opaque object passes in front of a source of light, a shadow will form
• light travels in straight lines called rays
• a solar eclipse happens when the moon comes between the sun and earth
• the shadow of the moon forms on the earth
• a lunar eclipse happens when the earth comes between the sun and moon
• the earth has a crust of solid rock
• under the crust is the mantle, which is molten rock that can flow
• in the centre of the earth is the core. it is made of the metals nickel and iron
• the outer part of the core is molten
• the inner part of the core is solid
• plates under the oceans are called oceanic plates
• some plates form the continents. they are called continential plates
• tectonic plates move slowly on the liquid rock called magma beneath them
• the plates where tectonic plates meet are called plate boundaries
• geological change happens most frequently at plate boundaries. this is because the tectonic plates are always moving
• sometimes, when tectonic plates move together, the rocks crumple and fold upwards
• volcanoes are usually formed at the plate boundaries when magma from the mantle rises up through cracks in the earth's crust