Lava Lamp
A lava lamp is an example of convection the heater in the base of the lamp heat up the fake lava. Due to the rapidly increased temp the lava expands making it less dense than the surrounding liquid. The less dense lava then floats to the top. When it is at the top it starts to get smaller and less dense than the surrounding liquid. This means it then floats down to the bottom again.
Radiator
In most houses we have a radiator. The heat given of by them is mainly produced by convection. The convector heater warms the air in contact with it this then becomes less dense and rises. The ceiling then forces the warm air to circulate warming the air around it. Finally when the air cools down it becomes denser again and falls down.
Atmospheric Convection
Solar Radiation heats the earth’s surface and this is transferred by convection. When a layer of air receives enough heat from the surface it expands becomes less dense and is pushed upwards by buoyancy. Colder heavier air sinks and reaches the higher cooler regions of the atmosphere. These convection currents cause local breezes, winds, thermals, cyclones and thunderstorms. At a larger scale it can produce global atmospheric circulation features.
Oceanic Convection
Solar radiation also affects the oceans. Warm water from the Equator circulates towards the poles. The cold polar water goes towards the Equator. Oceanic convection is also frequently driven by density differences. Known as thermohaline convection, and is of crucial importance in the global thermohaline circulation. It is quite possible for relatively warm, saline water to sink, and colder, fresher water to rise, reversing the normal transport of heat.
Mantle Convection
There are actually two convection currents occuring within the Earth. The outer core has an extremely rapid convective turnover of fluid metals which are responsible for the Earth's magnetic field. As heat from the inner and outer core heat the lower portion of the mantle, a second set of convective currents form. This mantle convection is extremely slow, as the mantle is a thick semi-solid with the consistency of a very thick paste. This slow convection can take millions of years to complete one cycle.